Immunology - E3 Flashcards
1
Q
Features of Innate Immunity
A
Prevent infection or eliminate a pathogen.
- Present in all individuals at all times
- Earliest response to infection (minutes/hours)
- Recognizes groups of similar pathogens (not “antigen-specific”)
- Not increased with repeated exposure to a pathogen (no memory)
2
Q
Examples of mechanical barriers (innate immunity)
A
Skin / mucosa
Movement of mucus by cilia
3
Q
Examples of biologically active substances (innate immunity)
A
- Anti-microbial proteins (skin, mucosa)
- Cytokines (IL-1, IL-6, TNF and others) *fever, depression, and anorexia
- Acute phase proteins: C-reactive protein (CRP) etc.
- Activation of Complement (Alternative and Lectin Pathways)
4
Q
What are cytokines?
A
“hormones of the immune system” (regulate immune response).
Cause fever, increased WBC, increased CRP, and recruit inflammatory cells to the site of infection. (Exp. IL-1, IL-6, TNF)
5
Q
What is C-reactive protein (CRP)
A
Example of an acute phase protein. Levels rise via the liver in response to inflammation.
6
Q
Innate immunity (Cellular) results in the activation of…
A
Activation of leukocytes (white blood cells):
Dendritic cells (DC) –> have PRR
Macrophages (Mf) –> phagocytosis, have PRR
Neutrophils –> phagocytosis, have PRR
Natural killer cells (NK cells) –> cytotoxicity
Mast cells and Basophils –> inflammation
Eosinophils
7
Q
Macrophages
A
Large, mononuclear phagocytic cells that are present in most tissues.
Macrophages are derived from blood monocytes (2-6% of WBCs).
8
Q
Neutrophils
A
(50-60% of WBCs), are phagocytic cells, also known as:polymorphonuclear neutrophils (PMN)
A major function of neutrophils is to enter infected tissues to engulf and kill extracellular pathogens, especially bacteria
9
Q
Eosinophils
A
(1-4% of WBCs)
- kill parasites that too large to be ingested by phagocytes.
- release substances that are toxic to helminths.
- involved in allergic responses.
10
Q
Mast cells
A
- Found in connective tissues throughout the body.
- Involved in response to parasites (especially helminths) and allergic responses.
11
Q
Basophils
A
(0.5-1% of WBCs) found in the blood and are thought to have a similar function as mast cells.
12
Q
Dendritic cells (DC)
A
Found in tissues and function todetect infection and elicit an early innate response
13
Q
What are pattern recognition receptors (PRR)?
A
Cells of the innate immune have receptors for pathogens called pattern recognition receptors (PRR).
Not specific for a particular bacteria species, recognize a GROUP of pathogens.
The innate immune system detects infection using about a few dozen.
14
Q
What is the microbial product recognized by PRRs?
A
PRRs recognize a pathogen associated molecular pattern (PAMP)
- Exp. dendritic cells and macrophages are activated when TLR-4 (a PRR) recognizes LPS (a PAMP) from gram negative bacteria.
15
Q
ADAPTIVE (ACQUIRED) IMMUNITY : Host defenses mediated by the_______________ and differentiation of antigen-specific lymphocytes (______________).
A
Host defenses mediated by the clonal expansion and differentiation of antigen-specific lymphocytes (B cells and T cells).
16
Q
Features of ADAPTIVE (ACQUIRED) IMMUNITY
A
Requires sensitization by antigen (Ag)
Develops over days/weeks
Response is antigen-specific
Results in immunological memory
17
Q
Adaptive immune responses can be classified as:
A
Humoral Immunity or Cell-mediated Immunity (CMI)
18
Q
Humoral Immunity
A
- mediated by antigen-specific antibodies (Ab) produced by activated B cells (plasma cells)
- Antibodies can be transferred to non-immune (naïve) recipients by immune serum (antiserum).
19
Q
Cell-mediated Immunity (CMI) are adaptive immune responses primarily involving _________.
A
Antigen-specific T lymphocytes (T cells).
20
Q
Can CMI can be transferred to naïve recipients by T cells?
A
Yes, but not by immune serum.
21
Q
Clonal expansion
A
Following activation by antigen, a B cell proliferates and produces a large clonal population of long-lived memory B cells and antibody-secreting plasma cells.
22
Q
Shape that Ab recognizes and binds is an _______
A
Epitope
23
Q
Explain how Ab response is polyclonal
A
On any antigen –> multiple shapes that are foreign and different Abs will recognize those epitopes.
Exp. Virus has many proteins, those proteins have many epitopes, and there are many B-/T- cells responding to those different shapes on virus.
^(Polyclonal, many clones of B-cells and T-cells will respond to any infectious agent).
24
Q
What are the primary lymphoid organs?
A
Where B and T cells undergo differentiation culminating in the expression of antigen-specific receptors.
B cells – bone marrow
T cells- thymus
25
What are secondary lymphoid organs?
- where lymphocytes encounter and respond to antigens.
- designed to trap antigen and facilitate antigen contact with lymphocytes.
Exp. Adenoid, Tonsil, Lymph nodes, Spleen, Peyer’s patches
26
Describe the structure of an antibody
Two H-chains (heavy chains) and two L-chains (light chains).
For a particular antibody, the H-chains are identical and the L-chains are identical. (2 identical antigen-binding sites)
27
What is the Fab region of an Ab?
Fab = ““fragment antigen binding”
- 2 Fabs/antibody molecule monomer, so each monomer contains two binding sites for an antigen.
- 2 Fab regions are identical
28
What is the Fc region?
Fc = determines the effector function(s) that will be activated by the antigen-antibody complex.
29
What about the structure of an Ab makes it specific?
N-terminal of heavy & light chains differs Ab to Ab (variable region, what makes Ab specific), rest is constant.
30
What is the antigen-binding site?
Variable region from one light chain and the variable region from one heavy chain combine together to form the shape that recognizes and binds antigen (antigen binding site).
31
Multiple Myeloma
Plasma cell (effector B cell) becomes neoplastic, growing out of control and crowding out the bone marrow.
Plasma cells --> produce large amounts of specific Ab. (normal Ab in structure, but is produced in abnormally large amounts.)
The AB produced by the neoplastic cells (a myeloma protein) is monoclonal (produced by a single clone)
32
Describe the Complementarity Determining Region (CDR) of an Ab
W/i variable regions --> 3 regions are hypervariable.
(Heavy chain has 3 CDRs, and light chain has 3 CDRs)
- These regions are up top, touching the antigen.
33
In mammals, there are five classes of Ig based on the ______________________________.
Sequence of the heavy chain constant region.
Constant region of heavy chain decides what the FC is (the effector part of the molecule).
34
A particular antibody will have one of the ___ possible _____-chain constant regions.
IgG1 (gamma-1)
IgG2 (gamma-2)
IgG3 (gamma-3)
IgG4 (gamma-4)
IgA1 (alpha-1)
IgA2 (alpha-2)
IgM (mu)
IgD (𝛿)
IgE (epsilon)
- Everyone makes all 9 of these isotopes.
35
The light chains associated with an antibody will be either ______ (k) light chains or _______ (l) light chains.
kappa (k) light chains or lambda (l) light chains
36
Two Ig classes can form polymeric Igpentameric IgM and dimeric IgA. Polymeric Abs have a single _______ protein bound to them.
J-chain protein
37
___ producing plasma cells always make pentameric ______ producing plasma cells makeeither monomeric ___ or dimeric ___
IgM producing plasma cells always make pentameric IgM
IgA producing plasma cells make either monomeric IgA or dimeric IgA
38
B-Cell Antigen Receptor (BCR)
All B cells have an antigen-specific receptor consisting of a monomeric Ig molecule (two H-chains and two L- chains)
Membrane-bound Ig is associated with a signaling molecule consisting of two proteins...
a heterodimer of _______ and ______.
Ig-alpha and Ig-beta.
39
Naïve B cells have BCRs of both___ and ___ classes.
The BCR of a memory B cell will be___, or ___ or ___ (never more than one class).
Naïve B cells have BCRs of both IgM and IgD classes.
The BCR of a memory B cell will be IgG, or IgA or IgE (never more than one class).
There are about 10,000 of these on each B-cell (all are identical on any given B-cell).
40
Describe agglutination (clumping antigen)
Because IgM is a pentamer (10 antigen-binding sites) this class is very effective at clumping antigen.
These large aggregates are more readily removed by phagocytes.
41
Describe neutralization of virus (or toxin) by antibody
Usually...
1. Virus binds to receptors on cell surface.
2. RCME of virus
3. Acidification of endosome after endocytosis triggers fusion of virus with cell and entry of viral DNA
Ab binds to the receptor on the virus --> blocks the binding to virus receptor, thus block fusion event (viral neutralization. IgG and IgA are the most effective neutralizing Abs.
42
Describe inhibition of Bacterial Adhesion by antibody
Usually...
1. Colonization of cell surface by bacteria via bacterial adhesions
2. Some bacteria become internalized and propagate in internal vesicles
Ab against adhesions block the colonization and uptake of bacteria
43
What is opsonization?
Coating of a microbe or other particle with a substance that makes the microbe more readily phagocytosed.
If put IgG on a microbe, it can be recognized more efficiently. (opsinization).
IgG is an important opsonin. (Free Ig does not cross-link Fc receptors, but aggregation of Ig on bacterial surface allows cross-linking of Fc receptors and thus activation of macrophage, phagocytosis, destruction)
44
Describe the mechanism of opsonization
Phagocytic cells (primarily macrophages and neutrophils) have Fc receptors that bind the Fc region of Abs, thus ingesting Ab-coated pathogens efficiently.
(Fc=part of the Ab that directs its “biological activity”. Here, Fc region facilitates phagocytosis of antigen by phagocytic cells.)
- When IgG binds to bacteria, the Fab is the portion of the Ab that actually binds the bacteria cell surface.
- The Fc portion of the Ab “sticks out” from the surface of the bound bacteria. Neutrophils and macrophages have Fcg-Receptors (FcgR) that will bind to the IgG-coated bacteria.
45
Describe Antibody-dependent cellular cytotoxicity (ADCC)
How Abs can enhance an innate effector function.
Antibodies can be made to viral antigens on the surface of infected cells or to tumor antigens on the surface of neoplastic cells.
1. Ab binds antigen on the surface of target cells.
2. The presence of FcgR (receptor for the Fc of IgG) on NK cells facilitates the ability of NK cells to recognize aberrant cells that are coated with IgG.
3. Cross-linking of Fc receptors signals the NK cell to kill aberrant cell.
4. Target cell dies via apoptosis.
46
How are NK cells an important component of innate immunity?
In contrast to B cells and T cells, NK cells do NOT express antigen-specific receptors.
NK cells recognize aberrant cells via receptors that recognize general features of infected or transformed cells. (the NKs express an Fc receptor and so induce some virus-infected or tumor cells to undergo apoptosis.)
47
Describe the immune response of mast cells and what this is an important protection against.
The inflammatory response resulting from mast cell degranulation functions in immunity to worms.It is also a key element in allergic reactions (mast cells release histamine).
Mechanism:
1. Fc-epsilon recognizes IgE antibody.
2. Multiple antigen cross-links bound IgE, causing release of granules which help get rid of bug.
48
What is unique about mast cell activation as opposed to opsonization and ADCC?
In contrast to opsonization and ADCC, mast cell FceRs bind IgE before IgE binds with antigen.
IgE already bound to FceRs on mast cells can then bind to antigen.
Mast cell pre-arms itself with IgE.
49
Antibody functions - who does it BEST?
Ag-specific receptor (BCR):
Agglutination:
Neutralization:
Ag-specific receptor (BCR): all isotypes
Agglutination: IgM
Neutralization: IgG and IgA
50
Antibody functions - who does it BEST?Complement activation:
Complement activation: IgM and IgG
(The complement system is a series of proteins that mediates host defense against various extracellular pathogens, especially bacteria)
51
Antibody functions - who does it BEST?Opsonization:
ADCC:
Mast cell activation:
Opsonization: IgG
ADCC: IgG
Mast cell activation: IgE
52
Which are the FcR-dependent functions of Abs?
Opsonization
Antibody-dependent cellular cytotoxicity (ADCC)
Mast cell activation
53
Which immunoglobulin is most highly concentrated in tissue fluid in blood?
IgG is the major immunoglobulin in the blood and tissues. Because IgG is present as monomers, it can diffuse out of capillaries into adjacent tissues.
54
Describe the distribution of IgM in the body.
IgM pentamers, because of their large size, are mainly confined to thebloodstream.
55
Describe the distribution of IgA in the body.
IgA dimers: major secretory immunoglobulin, found in mucosal secretions (milk, saliva, tears).
Large surface area of mucous membranes (digestive tract, respiratory tract, urinary tract, etc.) --> more IgA antibody produced each day than any other class.
56
Describe the importance of IgG in newborns
Babies are born with maternal IgG (the only antibody class that can cross the placenta.) IgG has a “half-life” of about 3-4 weeks, the longest of all antibody classes.
Thus, maternal IgG provides passive immunity to the newborn that is protective for 2-3 months.
Standard practice for tdap vaccine to be given (want baby to have high concentration to prevent neonatal tetanus)
57
The predominant Ig in secretions (saliva, milk) and at mucosal sites?
Secretory IgA (SIgA).
Dimeric IgA but MORE --> in addn to 2 IgAs, it has secretory component protein.
58
How does secretory IgA pass across epithelial cells to reach mucosal surfaces or enter secretions?
1. Dimeric IgA binds the polymeric Ig receptor (pIgR) at the basolateral membrane.
2. It is internalized and transported across the cell through the cytoplasm (transcytosis).
3. Dimeric IgA is then released from the apical surface of the cell onto the mucosa.
4. pIgR and dimeric IgA bind covalently and permanently. Only way to release IgA is a chainsaw (enzymatic cleavage).
5. Most dimeric ends up stuck to the receptor --> secretory component + dimeric IgA = secretory IgA.
59
What is a “common mucosal immune
| system”?
A “common mucosal immune system” is the concept that immune responses that occur at one mucosal site result in IgA secreting cells migrating, via the lymphatics and blood,
to distant mucosal sites.
60
What is an scFv, and why is it useful?
A scFv is an antigen-binding fragment (Fv) of an Ab engineered by coupling a VL domain and VH domain via a flexible polypeptide “linker.”
Thru genetic engineering, you can create a single chain Fv (just Ag binding site (VH and VL) and produce it as single polypeptide chain – so it can fold efficiently.
You can stick this on a toxin --> an immunotoxin results. Can use this to target tumor cells.
61
What is V(D)J recombination?
The DNA rearrangement mechanism that creates many billions of BCRs and TCRs using relatively few Ig and TCR genes
62
Which two proteins mediate V(D)J recombination and where are they found?
RAG-1 and RAG-2 mediate rearrangement of Ig genes in developing B cells (bone marrow) TCR genes in developing T cells (thymus).
63
Describe light-chain gene rearrangement.
One V segment gene and one J segment gene come together in the genome of a differentiating B lymphocyte to create a complete V-J gene unit that, together with the constant (C) region gene, codes for an entire antibody light chain.
An individual B cell will rearrange and express only one light chain using either the kappa locus or the lambda locus (never both).
64
What are the two main differences between light and heavy chain gene rearrangement?
1. The variable region of the heavy chain is coded for by three gene segments: a variable (V) segment, a diversity (D) segment (20 of these in humans), and a joining (J) segment.
2. The presence of multiple genes coding for the constant region of the heavy chain in the heavy chain Ig locus; one C gene for each of the nine human Ig isotypes.
65
How do naïve B cells produce IgM and IgD simultaneously?
C-mu and C-𝛿 constant region genes are the closest to the developing B cell's unique VDJ.
C-mu and C-𝛿 correspond to IgM and IgD heavy chain constant regions.
Via RNA splicing, the B cell can express BOTH IgM and IgD and both antigen receptors will have exactly the same antigen specificity. (Mature B aka Naive B)
66
What are the three means of generation of Antibody Diversity?
1. Germline: multiple inherited V, D and J
2. Combinatorial: V + D + J and H + L
3. Junctional: imprecise joining of V, D, and J gene segments by exonucleases and TdT.
(TdT = terminal deoxyribonucleotidyl transferase)
67
Describe the mechanism of TdT (terminal deoxyribonucleotidyl transferase) and how it contributes to junctional Ab diversity.
When gene segments are excised for V(D)J recombination, exonucleases randomly “chew back” a variable number of NTs from the ends of the joining segments.
TdT randomly adds entirely new NTs to the ends of the segments prior to their joining --> makes the junctions between V, D, and J gene segments highly variable --> important for the creation of diversity at the antigen binding site.
68
Describe Somatic Hypermutation (SHM) and how it contributes to Ab diversity.
*Occurs only in B-cells
POST ANTIGEN ACTIVATION, increase in the affinity of antibody for the antigen is observed --> Somatic hypermutation (affinity can increase 100 to 1000-fold over time)
Refers to random point mutations that occur in the variable region (antigen-binding sites) of immunoglobulin heavy and light chains in the B cells of an expanding clone.
(“survival of the fittest” = B cells making high-affinity BCR)
69
B cells and T cells use V(D)J recombination to generate antigen-specific receptors
B cells rearrange _____
T cells rearrange _____
B cells rearrange Ig loci
(Igh and either Igk or Igl)
T cells rearrange TCR loci
(TCRa and TCRb, or TCRd and TCRg)
70
A complete deficiency of either RAG1 or RAG2 causes what?
Absence of both B cells and T cells and a complete loss of adaptive immunity. Can’t make receptors.
71
Class Switch Recombination (CSR)
After activation by antigen, a B cell can “switch” to produce different classes of antibody molecules, such as IgG, IgE, and IgA, while still retaining the same antigen specificity.
Same heavy chain VDJ rearranged genes are moved next to a different constant region gene (either Cg, Ca, or Ce). ONLY the heavy-chain C region is changed, thereby preserving the antigen specificity of the B cell.
72
While individual mature (naïve) B cells can produce _______________ on their cell surfaces, after class switching, an individual B cell can _________________.
While individual mature (naïve) B cells can produce both IgM and IgD on their cell surfaces, after class switching, an individual B cell can only produce one of the “switched isotypes” (i.e. IgG or IgE or IgA).
73
What are some shared features of Class Switch Recombination (CSR) and Somatic Hypermutation (SHM)
Class Switch Recombination (CSR) and Somatic Hypermutation (SHM)
- B cell-specific mechanisms
- Occur during clonal expansion
- Occur in germinal centers of secondary lymphoid organs.
- Both mediated by AID (activation-induced cytidine deaminase)
74
What does deficiency of AID (activation-induced cytidine deaminase) lead to?
AID deficiency results in:
- lack of class-switching to IgG, IgA, IgE (due to defective CSR)
- lack of high-affinity antibodies (due to defective SHM)
- AID deficiency is one form of hyper-IgM syndrome
75
What creates great diversity of BCRs (Ig) and TCRs?
process of V(D)J recombination
76
Name and describe the stages of B cell development
1. Pre-B: have undergone a complete VDJ heavy chain rearrangement. But no light chain rearrangement (kappa nor lambda) light chains are produced at this stage. Heavy (μ-chain) cannot form IgM molecules.
2. Immature B: underwent light chain rearrangement (kappa or lambda produced). So cells express membrane IgM (a MONOMER, not pentamer which is secreted by plasma cells)
* NEGATIVE SELECTION: cells that have created, by random V(D)J recombination, a self-reactive (autoreactive) Ig are removed.
3. Mature B: express both membrane IgM and membrane IgD (via alternative splicing), both of which function as BCRs (B-cell receptors for antigen). *antigen specificities of IgM and IgD on SAME B-cell are identical.
Mature B cells leave the bone marrow --> migrate to the 2° lymphoid organs & recirculate. Capable of being activated by antigen to produce plasma cells and memory cells.
77
Describe the difference between passive and active immunity
Passive Immunity --> mediated by the transfer of pre-formed antibodies (Maternal IgG transferred to fetus, or immune serum injected into a naïve recipient)
Active Immunity --> mediated by an adaptive immune response to antigen (by infection or vaccination)
78
Give examples of Natural and Artificial PASSIVE immunity
Passive --> receiving pre-formed Abs
Natural
- Maternal IgG transferred to fetus by placental transfer via the neonatal FcR (FcRn) (lasts 2-3 mo.)
- Maternal secretory IgA transferred via colostrum/milk
Artificial
- Injection of immunoglobulin
- RIG (rabies immune globulin, from serum of people previously immunized with the rabies vaccine)
- IVIG (intravenous immunoglobulin)
- Monoclonal antibody (mAb) (drugs)
79
Give examples of Natural and Artificial ACTIVE immunity
Active Immunity --> adaptive immune response to antigen
Natural
- Infection with pathogen
Artificial
- Immunization (for example, killed or attenuated pathogen)
80
What is Intravenous Immunoglobulin (IVIG) (Intravenous Immune Globulin) used for?
An example of passive immunization. IVIG is prepared from very large pools of donors and administered i.v. to individuals deficient in humoral immunity.
IgG (the major class in serum) --> half-life of about 3 weeks in the body, IVIG administered ~ once a month.
FDA APPROVED USES
- Primary humoral immunodeficiency diseases
- Children with HIV
- autoimmune
- inflammatory diseases
81
What is an ENZYME LINKED IMMUNOSORBENT ASSAY (ELISA) and give an example of its use.
ELISA uses antibodies coupled to enzymes to detect substances in solution. When substrate is added --> color change.
Exp. pregnancy test
- binding of human chorionic gonadotropin (HCG) in the serum of pregnant woman to Ab specific for HCG that has been bound to a test strip. The color rxn of a positive test is bc enzyme linked to the anti-HCG antibody converts a colorless substrate into a colored product.
82
What are monoclonal antibodies (MAbs)?
| How is human anti-mouse antibodies (HAMA) avoided?
Abs produced by a single clone of B cells (can have unlimited supply of a homogeneous Abs)
MAbs originally produced in mice, but use in humans --> HAMA.
Solution: chimeric or humanized antibodies (have only the CDRs (complementarity determining regions) of the antigen-specific mouse antibody “grafted” into a human immunoglobulin sequence.
83
chimeric mAbs end in: _______
| humanized mAbs end in: _______ fully human mAbs end in: _______
chimeric mAbs end in: ximab
| humanized mAbs end in: zumab fully human mAbs end in: umab
84
APCs --> essential for activating _______ immune responses.
The important antigen-presenting cells:
APCs --> essential for activating adaptive immune responses
Dendritic cells * most effective
Macrophage/monocytes
B-lymphocytes
85
APCs have toll-like receptors which recognize ______ and produce_____.
Toll Like Receptors recognize PAMPS (Pathogen Associated Molecular patterns) and produce cytokines (IL-1 and TNF)
86
Functions of IL-1 and TNF
1. Increased STICKINESS of endothelial cells.
- Role in acute inflammation. (activate endothelial cells)
2. Activation of liver
- releases acute phase proteins like CRP (indicator of level of activity of disease)
3. Acts on hypothalamus
- fever, depression, anorexia ("sickness cytokines"
87
Group of cytokines
Chemokines (chemotactic cytokines): attract other cells to the site
88
IFN α and IFN β
IFN α and IFN β - Antiviral cytokines
89
IL-12
Key in turning on T-cell system
| - Activates TH1 cells and NK cells and production of IFN-γ by T cells + NK cells
90
IL-10
Inhibitory cytokine
| - Turns down immune responses
91
How do cytokines end up interacting with T-cells?
When TLR activated on APC --> all cells prod cytokines --> move to draining lymph nodes --> interact with T-cells
92
When are T-cells activated?
When their T-cell receptors interact with foreign peptide inside the groove of a Class II Major HIstocompatability Antigens (MHC) molecule
93
Describe the gene structure of the human MHC.
What do Class II / Class I molecules contain?
MHC= most ________ system in biology
MHC - an area on short arm (p) of chromosome 6. On short arm there is the HLA region --> codes for genes that make antigen and are crucial for transplantation. (whole thing: "haplotype")
Class I molecule (A, B, C)
Class II molecule (DP, DQ, DR)
MHC= most polymorphic system in biology
94
MHC (HLA) proteins
- _______ on tissues recognized by a recipient’s immune response
- are attacked after a _______ causing _______
MHC (HLA) proteins
- antigens on tissues recognized by a recipient’s immune response
- are attacked after a transplant procedure causing transplant rejection
95
Since every individual inherits 2 haplotypes (one from each parent), if a couple has 5 children, which child would be identical to one of their siblings?
5th child
96
MHC class I molecules are associated with which invariant polypeptide? What is its function?
Beta-microglobulin: constant, not coded for within MHC gene complex, resides on another chromosome.
It tissue destroyed, beta macroglobulin is sent off *indicates tissue injury
97
Where are MHC class II molecules presented?
MHC class II molecules are presented ONLY on antigen presenting cells.
98
Where are MHC class I molecules presented?
MHC class 1 molecules are found on all cells of the body other than red blood cells.
99
What does a T-cell "see"
MHC with a peptide in its groove
100
MHC Class I molecule
- peptide binding groove is produced by the _________.
- __________ is constant on all MHC Class 1 molecules
MHC Class I molecule
- peptide binding groove is produced by the polymorphic alpha chain.
- beta-2-microglobulin is constant on all MHC Class 1 molecules
101
Ankylosing spondylitis (bamboo spine)
Almost all patients are HLA B27
102
Narcolepsy
Associated w/ DR2 or DQ1 in 98% of patients
103
Most patients with IDDM are ____ or ____
DR3 or DR4 (particular alleles of HLA locus)
104
RA is associated with HLA ____
RA --> HLA DR4
105
IL-6
Cytokine produced by an APC
| IL-6 (activates the bone marrow --> increased white cell count)
106
Both Class I and Class II MHC molecules have a...
peptide binding cleft
107
T cell receptor (TCR)
- antigen-binding, unable to recognize free antigen - need antigen presented by an APC (dendritic cells, macrophages, monocytes, B cells)
- same family as Ig (same recombination events are used to form TCR)
- TCR is same on T cell at every stage at development (no change like SHM)
- NOT secreted on activation (unlike Ig which is secreted)
- either αβT cells* or γδT cells
108
CD3
Invariant, found on all T cells, expressed in non-covalent association with TCR
CD3 + ζ (zeta) polypeptides transduce signals through the TCR
Signals ultimately lead to changes in cell's pattern of gene expression in nucleus
109
CD19 and CD20
Markers of mature B-cells (analogous to CD3 and T cells)
110
Different expressions of CD3
What makes a T cell a T cell is whether it expresses CD3
- Either express alpha beta TCR or gamma TCR (non-overlapping functions)
111
Function of T cells, CMI or humoral?
Respond to pathogens and protein antigens that get into host cells. Uptake: Infection, or endocytosis or phagocytosis.
Mainly respond to PEPTIDES on surface of host cells.
CMI
112
Antigen recognition by αβTCR T cells
3 way interaction (1. MHC expressed on host cell, with 2. peptide derived from an antigen, that peptide is bound to MHC molecule --> combo of these binds to 3. TCR on T cell)
113
Differences between two classes of MHC molecules?
MHC class I – expressed on all nucleated cells
MHC class II – expressed constitutively only on antigen presenting cells (APC) = DC, B cells, and macrophages (+ thymic non-lymphoid cells)
114
The two classes of MHC molecules interact with different molecules expressed on different sets of T cells...what are these interactions?
MHC class I interacts with CD8 expressed on CD8+ cells
MHC class II interacts with CD4 expressed on CD4+ cells
115
2 functions of CD4 and CD8 (coreceptors on αβTCR T cells)
1. Specific adhesion molecules: they bind to different MHC molecules
2. Signal transduction molecules - enhance signal through TCR (*need far less antigen to get a response if you have a coreceptor)
116
Specificity of CD4 and CD8
In humans CD4 and CD8 are expressed on more cell types than T cells. (Also expressed on myeloid cells: macrophages and dendritic cells.)
117
Major functions of CD4, CD8
CD4 function: cytokine synthesis, T helpers (Tregs)
CD8 function: 'killer' or cytotoxic T cells, recognize and destroy infected cells
118
Thymus
primary lymphoid organ for T-cell development, gets smaller during puberty
119
DiGeorge Syndrome
- Thymus absent or undeveloped
| - No mature T-cells --> recurrent infections as a young child
120
T cells will respond with the ____ they have seen on the cortical epithelial cells
T cells will respond with the MHC they have seen on the cortical epithelial cells
121
Positive selection
TCR of the double positive cell interacts with MHC class I and II molecules (and peptides) expressed by epithelial cells in the thymic cortex
Results in survival and differentiation of the thymocyte.
Majority of double positive cells are not selected – die by apoptosis.
122
What is lineage choice
Committing to developing into either the CD4+ or the CD8+ T cell lineage.
Double + cell (αβ CD4+CD8+(CD3+)) downregulates CD8 or CD4, cell expresses only CD4 or only CD8 --> becomes a single + cell
123
Describe negative selection
As T-cells move through, their TCR and coreceptor interacts with MHC molecules expressed on thymic dendritic cells and medullary epithelial cells
- If affinity between T cell and self is TOO high eliminated
- Left with cells with low/intermediate affinity to self.
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What does a defect in negative selection cause?
Autoimmune diseases
Exp. APECED = autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome
^ Affects multiple endocrine organs, (adrenals, parathyroids and thyroid), and candidiasis develops
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Outcome of T-cell differentiation
1. No response to self-molecules
| 2. Respond to foreign antigen ONLY when bound to one of your HLA (MHC) molecules (specific MHC encountered in thymus)
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MHC restriction of T cell responses
Crucial requirement for MHC expression in T cell responses.
The TCR interacts with a peptide fragment of a protein antigen bound to a major histocompatibility complex (MHC) molecule expressed at the surface of the host cell.
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A developing αβT cell that survives positive selection becomes “educated” to the MHC molecules expressed by the thymic cortical epithelial cells, what does this mean?
T-cell will now respond to antigen ONLY when the antigen is bound to the MHC molecules that the developing T cell encountered in the thymus, either MHC class I or MHC class II
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2 major sets of protein antigens
Exogenous antigens: taken up from outside environment usually by APC (dendritic/macrophages), include pathogens and 'harmless' antigens (vaccine protein) --> MHC I & CD4 response
Endogenous antigens: synthesized inside host cells (usually as result of infection of the cell) --> MHC II and CD8 response
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Key steps of processing of an exogenous antigen in the MHC class II pathway
(CD4+ response)
1. Antigen is taken up by APC cells into vesicles.
2. Vesicles acidify, fuse to lysosome where antigen is proteolyzed.
3. Antigen-containing vesicles fuse with MHC II containing vesicles (synthesized in RER as α + β chains) where 12-22 AA peptides with the appropriate motif selectively bind to MHC II.
4. MHC II + Ag complex vesicle fuses to cell surface to present to CD4+ T Cells.
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Fate of exogenous protein antigens
Exogenous protein antigens (pathogens, “harmless” antigens) are taken up by specialized host cells, APC.
Some peptides associate with MHC class II and are presented to CD4+ T cells.
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Key steps of processing of an endogenous antigen in the MHC class I pathway
(CD8+ response)
1. Antigen is produced inside the cell (viral protein).
2. Antigen is proteolyzed by proteasome to 8-9 AA peptides.
3. Antigen peptides with the proper motif are transported into the RER where MHC I (α-chain + β2-microglobulin) is synthesized, allowing association.
4. MHC I + Ag complex exocytoses to cell surface to present to CD8+ T Cells.
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Peptide binding to MHC molecules is selective. Describe this
Protein antigen is being broken down into peptides which preferentially bind to different parts of the HLA binding groove, depending on sequence.
Due to motif selectivity of MHC binding, different people respond to different parts of a given protein.
- Exp. Some peptide may bind to his HLA-B27+ that may cause him to be more susceptible to AS
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Some ___ alleles are associated with autoimmune syndromes (diabetes, ankylosing spondylitis[AS]…)
HLA alleles
Some combination of specific HLA allele and a specific peptide results in pathology.
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Activation of the T cell requires 2 signals
1. Signal through TCR
2. Signal through costimulators
(^costimulator pairs...
B7 - CD28
CD40 - CD40 Ligand)
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Key APC for the activation of naïve T cells
dendritic cell
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DC maturation
1. Immature Dendritic Cell (DC=APC) recognizes and takes up exogenous antigen with Toll-Like Receptors (TLRs=pattern recognition receptors) or phagocytosis.
2. Dendritic Cell is induced to mature by antigen loading to MHC II, causing it to upregulate MHC II, B7, and CD40 (another co-stimulator), while allowing it to migrate out of the tissue to nodes.
3. This TLR interaction is necessary to cause CD4+ activation in the node. (Need co-stimulator)
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Examples of antigen uptake without DC maturation
Self-proteins can be processed and presented by MHC II, but bypass TLR activation, therefore do not cause DC maturation or T cell activation.
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2 T-cell turn off signals
CTLA-4 (activated T) binds to B7 (APC)
PD-1 ("exhausted" T) binds to PD-L1 or PD-L2 (on tumors or normal cells)
^interactions --> negative signal to T cell
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CTLA-4
CTLA-4 competes with CD28 for binding to B7
| CTLA-4 interaction with B7 turns off activated T cell
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PD1/PDL1
PD-1 expressed on “exhausted” activated T cells, in chronic conditions such as cancer
PD1/PDL1 turns T-cell off
* interaction between these 2 is negative
* checkpoint therapy for tumors. Anti PD-1 or anti PD-L1 --> blocks interaction, T cell response continues --> death of tumor cells
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Naïve CD4+ T Cell Activation requires
1. Peptide + MHC II complex interaction between APC and TCR.
2. Costimulator pairs on APC (B7) and T cell surface (CD28)
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Early events of Intracellular pathways in T-cell activation
1. Build up of signal-transduction complex
2. Activation of tyrosine kinases (*zap-70 --> imp in T cell function because ppl who don’t have this are profoundly immunodeficient)
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Results of CD4+ T cell activation
1. Synthesis of cytokines and cytokine receptors (IL-2 and IL-2 receptor)
2. Proliferation (expansion of clone size)
3. Changes in expression of adhesion molecules (effector T cell leaves node, moves into tissues to combat pathogen)
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What are super antigens and what do they result in?
Protein antigens that are components of pathogens
Result in activation of huge numbers of αβ TCR T cell
"Cytokine storm" Massive proliferation of cytokines can be fatal (toxic shock syndrome)
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How does humoral immunity rapidly evolve high affinity antibodies?
SHM and selection (“survival of the fittest” = B cells making high-affinity BCR)
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What diversifies Ab effector functions?
Class Switch Recombination (CSR) (from IgM to IgG, IgA, and IgE)
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Where and when do SHM and CSR occur?
in germinal centers ONLY in B cells that have been stimulated by antigen AND have received signals from T cells
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Fate of exogenous and endogenous protein antigens
Endogenous protein antigens come from inside a host cell, generally as a result of infection of the cell.
Some peptides associate with MHC class I, and are presented to CD8+ T cells.
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Cytokine-cytokine receptor interaction
polymerization of receptor
activation of signal transduction
Monoclonal Ab specific for cytokine or receptor --> tx for autoimmune/inflammatory condn
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How different subsets of CD4+T cells develop
Interactions between pathogens and innate immune cells (DC and NKs) --> different cytokines early in response --> influence differentiation of Naïve CD4 in presence of peptide derived from pathogen on left
(happens in presence of APC interacting with naïve CD4 splitting into subset of specific CD4 cells)
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Th17 subset response
Trigger formation of Th17 --> triggers cytokine IL17 (activate cells at mucosal surfaces – key protection against fungi and extracellular bacteria)
Exp. of polarization of immune response by pathogens (some Th17, some IL17)
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Nearly all proteins are thymus-dependent (TD) antigens, meaning...
TD ag require help from CD4+ T helper cells for B cells to synthesize antibody
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How do cytokines direct specific immune response?
Influence B cell class switch recombination (produces different Abs)
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What causes defective class switch recombination?
Important recombination between CD40 and CD154. upregulates AID. Required for class switch recombination. If defective, no Class switch --> hyper-IgM syndromes
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Thymus-independent (TI) antigens
```
Exp. Lipopolysaccharide (Gram-negative bacteria)
Capsular polysaccharides (Strep. pneumoniae and Haemophilus influenzae b)
```
- responses --> no memory (IgM predominates)
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Must be activated before they kill their target (virus-infected or tumor cells)
CD8+ T cells
| activation is separated from killing phase
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Explain the components of CD8+ that kills virus-infected target
Perforin, granzymes (apoptosis), interaction between FasL and Fas on target cell (apoptosis)
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Cytokine-cytokine receptor interactions
1. Polymerization of receptor
| 2. Activation of signal transduction
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To block cytokine-cytokine receptor interactions
- mAb specific for cytokine or receptor
- inhibit kinase
Tx for autoimmune or inflammatory conditions like RA and psoriasis
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CD4+ T cells cooperate with other leukocytes in what ways?
- Act as T helpers for B cells to make Ig;
- Activate Cell Mediated Immunity (CMI, CD8+ T cells, NK cells, and macrophages)
- Activate effector cells such as eosinophils and neutrophils.
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What are the subsets of CD4+ T cells and their "signature" cytokines?
Th1 IFN-gamma
Th2 IL-4, IL-5, !L-13
Th17 IL-17
Treg TGF-beta and IL-10
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How do different subsets of CD4+T cells develop?
Cytokines present during the activation of CD4+ T cells drive the differentiation of the naïve CD4+ T cell into a particular subset – TH1, TH2, TH17, or Treg.
Cytokines influencing differentiation of CD4+ T cells are generally derived from cells of the innate immune system, and particularly from dendritic cells. (Cells of the innate immune system have critical role in shaping the pattern of the adaptive immune response)
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Cytokines secreted by different subsets of CD4+T cells activate different sets of _______ cells
Cytokines secreted by different subsets of CD4+T cells activate different sets of effector cells (macrophages, NK cells, eosinophils, B-cells, etc.)
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TH1 CD4+
- Formed when innate immune cells (DCs; APCs) activate and secrete IL-12.
- Secrete IFN-γ to activate CMI (macrophages, cytotoxic CD8+ T cells, NK cells)
Also activates classical complement pathway, by inducing B cell class switch to produce IgG3. → Fights viruses and bacteria.
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TH2 CD4
- Formed in the presence of IL-4
- Secrete IL-4 and IL-13: Activate B cell class switch to produce IgE, IgG4
- Secrete IL-5: Activates eosinophils. → Fights parasitic worms and responds to allergens
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Th17
- Secrete IL-17: Pro-inflammatory response attracting neutrophils + immune cells to mucosa
- Responds to fungi/bacteria and autoinflammatory responses (psoriasis, arthritis)
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Thymus Dependent Antigens
Nearly all proteins are thymus-dependent antigens (TD ag)
- require Helper T Cells to interact with B cells inducing CLASS SWITCH to the appropriate antibody production. (Requires interaction of a T cell and B cell, both specific for the same Ag)
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Antigen-specific B interacts with antigen-specific T in....
Lymph node.
The interacting T and B cells form a germinal center, the site of intense B cell proliferation, somatic hypermutation, and class switch recombination.
In this T-B interaction, both cells are activated: the T helper cell to synthesize cytokines and the B cell to synthesize antibodies that may be IgM, IgG, IgA, or IgE.
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Products of interactions in germinal centers
```
1) Class-switched
plasma cells (IgG, IgA or IgE)
```
2) Memory B cells (IgG+, IgA+ or IgE+)
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Which cytokines made by CD4+ T cells influence B cell class switch recombination?
CYTOKINE ANTIBODY
IL-4 IgE (Allergy, parasites)
IFNγ IgG3 (Complement activation)
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What causes defective class switch recombination?
Impaired recombination between CD40 and CD154 (which usually upregulates AID, which is required for class switch recombination.)
If defective, no CSR --> hyper-Igm syndromes (HIGM)
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Thymus-independent (TI) antigens
TI antigens do NOT require T cell help for B cells to synthesize antibody
Usually polysaccharide (LPS, capsular polysaccharides)
No class switch; no memory B response; IgM only.
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CD8+ T cells (killer or cytotoxic T cells) must be ________ before they kill their target
virus-infected or tumor cells.
Most viruses (HIV) use _____ to help with this.
CD8+ T cells (killer or cytotoxic T cells) must be activated before they kill their target
virus-infected or tumor cells.
Most viruses (HIV) use CD4+ to help with this.
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CD8+ T cells that emerge from the thymus do not kill targets: they must first be activated to proliferate and differentiate into effector cells. How is this accomplished?
The two-signal paradigm for T cell activation we described for CD4+ T cells also applies to the activation of CD8+ T cells:
1st signal: peptide/MHC interacting with the TCR
2nd signal: costimulator signals, presented by an APC, particularly a dendritic cell.
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Activation of CD8+ T cells induces what two things?
Activation of CD8+ T cells induces...
1. formation of granules that contain cytotoxic proteins (perforin, granzymes)
2. expression of the cell surface molecule Fas ligand (CD95).
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Mechanism of perforin and granzymes? (Which are released from granules of CD8+ T cell)
Perforin: polymerizes to form ring-like transmembrane channels or pores in the target-cell membrane --> increase in permeability of the cell membrane contributes to the eventual death of the cell
Granzymes --> serine esterases that pass into the target cell through the pores created by polyperforin molecules. These interact with intracellular components of the target cell to induce APOPTOSIS.
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CD8+ T cell pathway of target cell killing via Fas ligand
Interaction of the molecule CD95 (Fas ligand) on the CD8+ T cell with Fas, a surface molecule expressed on many host cells --> APOPTOSIS of the target cell
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T-cell responses in tumor therapy
- Checkpoint therapy = blocking T-cell turn off signal(s) (Exp. mAb that block PD-1/PD-L1 and/or CTLA-4/B7)
- Engineered chimeric antigen receptor (CAR) T cells (genes for new receptor inserted in patient’s T cells)
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Generation and use of chimeric antigen receptor (CAR) T cells
(AKA CAR-T cells)
Engineering T cells to contain a new receptor, inserting CAR-T into patient’s T cells
Major success to date – killing B cell tumors expressing CD19
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What is meant by somatic hypermutation (SHM) and class-switch recombination (CSR)?
SHM --> high rate of point mutation in the DNA coding for the variable portion of the antibody molecule’s heavy and light chains (which together form the antigen-binding site).
CSR --> results in “switching” from the expression of both IgM and IgD to the expression of one of the following classes (isoypes): IgG (IgG1, IgG2, IgG3, or IgG4), IgA (IgA1 or IgA2) or IgE.
- allows the immune response to develop and utilize the various effector functions and distribution of IgG, IgA and IgE while maintaining the antigen specificity of the mature B cells (IgM and IgD on their membranes) that first responded to antigen
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Where do SHM and CSR occur?
| At what point in B-cell development does each occur?
Germinal centers of secondary lymphoid organs (e.g., tonsils, spleen, lymph nodes).
SHM and CSR occur only in B cells that have been activated by antigen to proliferate and differentiate (clonal selection)
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How dos SHM lead to an increase in average affinity of Ab response over time & with repeated immunization?
SHM can slightly change the antigen-binding site during clonal expansion.
- those B cells that develop B cell receptors (BCR) with increased affinity for antigen will have a selective advantage and undergo more extensive proliferation.
SHM, + selection of B cells producing high-affinity BCR, results in a great increase in the average affinity (as much as 100-fold) of an antibody response over time and with repeated immunization.
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What is the typical structure and function of IgM?
Membrane-bound IgM: monomer (2 H-chains and 2 L-chains).
Secreted antibody IgM: pentamer consisting of five IgM monomers and one J-chain polypeptide.
IgM --> agglutinates (clumps) antigens which facilitate phagocytosis
(Note: IgM and IgG are potent activators of the complement system)
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What Ab functions are severely limited in a patient with HIGM 1 and which isotype (class) carries out each of the functions lost in these patients?
HIGM -->IgG, IgA and IgE are extremely low or absent.
IgG --> neutralization of viruses and toxins, opsonization, and NK-cell mediated antibody-dependent cellular cytotoxicity (ADCC). IgG is the only Ig class that crosses the placenta.
IgA --> neutralization of viruses and toxins and inhibition of bacterial adherence.
--> in the blood and tissues (as a monomer) and in secretions (including milk) and mucosal sites as a polymeric Ig (mostly dimers)
IgE --> defense against parasitic infections via mast cell activation.
- bound to FceR on mast cells. If IgE on mast cells are crosslinked by binding the same Ag, mast cells are activated and release histamine and other inflammatory mediators.
IgE-mediated mast cell activation is also a key mechanism in allergy
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Which type of immunity is provided by IVIG?
Describe the timeline that it is administered.
Intravenous Ig (IVIG): pooled Ig (mostly IgG) from many donors. Tx with IVIG --> PASSIVE (HUMORAL) immunity.
For long-term use, IVIG administered every 3-4 weeks by infusion (half-life of IgG is about 4 weeks).
Therapeutic monoclonal Abs, such as Humira (anti-TNF, immunosuppressive), can be self-administered at home using pre-filled syringes. A maintenance dose of Humira is typically administered every other week.
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What is the difference between active and passive immunity?
Passive immunity --> administering pre-formed antibodies and is transient.
Active immunity --> activation of B cells and T cells by antigen (via infection or vaccination).
*only active immunity results in --> effector cells (plasma cells and activated T cells) and memory B cells and memory T cells.
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How is it possible for a pt with HIGM to have B cells which express both IgM and IgD on their surface, in the absence of class switch recombination?
The vast majority of B cells in immunocompetent people are naïve B cells that express both IgM and IgD on their membranes as BCRs (IgM+ IgD+ cells = mature B cells).
Simultaneous expression of both IgM and IgD does not require CSR. It occurs through alternative RNA splicing of a long RNA transcript that includes the nucleotide sequence for the heavy chain variable region (VDJ) and the constant region sequences for BOTH IgM (C-miu) and IgD (C-delta)
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What type of immunity is conferred by a DTP vaccine?
How is this different from IVIG?
The DTP vaccine induces active, humoral immunity.
Following a minimum of three doses of DTP, pt will have protective Ab levels for a number of years.
Vs. passively transferred Abs such as intravenous immunoglobulin (IVIG) or tetanus immune globulin (TIG), which provide only transient protection for 2- 3 months.
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A few hours following a pt's DTP vaccination, the injection site is somewhat red and swollen. Pt also has a mild fever following the vaccination. How would you explain these mild side-effects?
The DTP vaccine is not a live vaccine, so there is no possibility of infection.
Since the injection-site inflammation and mild fever occurred after just a few hours of Maria’s first DTP vaccination, the fever and injection site inflammation are likely due to an innate immune response (especially IL-1 and TNF production) to the antigens and adjuvant in the vaccine (adjuvant --> any substance that, when mixed with an antigen, enhances the antigen-specific immune response).
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Adjuvant
Substances distinct from antigen --> enhance T-cell activation by promoting the accumulation of APCs at a site of antigen exposure.
They are also thought to increase cytokine production and expression of co-stimulator molecules by APC’s
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What role do antigen-presenting cells (APC) and T cells play in the immune response to the DTP vaccine?
What are the key interactions that occur between these cells?
APC (primarily DCs) initially take up the protein antigens in the DTP vaccine.
- proteins are cleaved into short peptides (about 12-20 amino acids) in intracellular acidic vesicles.
- peptides with the appropriate binding characteristics associate with MHC class II molecules and MHC II/peptide molecules are transported to the DC surface.
- The antigen-bearing DC migrate to a draining lymph node and present the MHC II-associated peptides to CD4+ T cells.
*Importantly, the DC will also provide an activation signal to the CD4+ T cells via the costimulator molecule B7 (on the DC) and CD28 (on the T cell).
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What class of vaccine-specific antibodies would be found in a pt's serum 1 week following first immunization with DTP?
How is an individual capable of producing antibodies to any microbe or microbial protein?
Pt would have vaccine-specific Abs (specific for diphtheria, tetanus, and pertussis) of the IgM class 1 week after receiving her first dose. The antibody titer (concentration) of at one week would likely be low, but increasing.
Individuals can make highly specific Abs to virtually any microbes or microbial proteins due to the enormous number of naïve B cells and T cells, each with a unique receptor for antigen. (CSW)
The relatively small number of lymphocytes that are specific for any one antigen (such as a toxin) will be amplified through proliferation of antigen-specific B-cell and T-cell clones.
The fact that each individual has lymphocytes (B and T cells) specific for any antigen and that these lymphocytes can be activated to proliferate (clonal expansion) and differentiate into effector and memory lymphocytes are key features of the clonal selection hypothesis
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Antigen specificity and memory are features of what type of immunity?
Adaptive immunity
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Clonal Selection
1. The immune system = heterogeneous population of billions of different lymphocytes.
2. Each individual lymphocyte --> specific for a single antigen.
3. Each lymphocyte has a unique surface receptor for antigen, i.e. the receptor is clonally expressed. B cells have an antigen-specific receptor (BCR) which is membrane-bound antibody.
4. Only a small # of lymphocytes will recognize a particular antigen.
5. Recognition of an antigen (i.e. interaction of the antigen with the lymphocyte receptor) signals proliferation (clonal expansion) results --> large clone of cells, all expressing receptors that recognize the same antigen.
6. Proliferating lymphocytes will eventually differentiate into either effector cells or memory cells.
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Most adaptive immune responses result in all of the following...
a) Effector B cells (plasma cells) that secrete antigen-specific antibodies.
b) Effector T cells (CD8+ [cytotoxic T cells] and CD4+ [T helper cells]).
c) Long-lived memory T cells.
d) Long-lived memory B cells (underwent isotope switch to IgG, IgA, or IgE)
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Primary and Memory immune responses
The first exposure to an antigen results in the activation of naïve B cells, B cells that have not “seen” antigen before. In this primary response, both plasma cells and memory cells are generated.
In primary responses, the T cell predominantly synthesizes IL-2 and the B cell produces IgM.
If the T cell synthesizes IL-4, B cells switch to producing predominantly IgE.
If the T cell produces IFN-γ, B cells switch to producing IgG subtypes such as IgG3 that acti- vate complement.
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Secondary or Memory responses
Presence of an expanded population of memory B cells results in a more rapid and more robust humoral immune response (i.e. more antibody in less time).
The initiation of Ab synthesis in the secondary response occurs more rapidly (shorter lag phase) and the antibody titer increases at a faster rate and reaches a greater maximum.
(*the memory response measured in blood will be mostly IgG and will typically have less IgM than the primary response. Abs made in the memory response will also have a higher average affinity for antigen due to SHM and the selection for high-affinity B-cell clones.
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Is the Ab response to DTP directed by Th1 cells or Th2 cells?
The diphtheria, tetanus and pertussis vaccine is administered as an intramuscular injection and would be expected to elicit a strong Th1 response (producing IFN-) and promote class switching to IgG.
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If, following a completed course of immunization for tetanus, pt is exposed to tetanus toxin, how would her vaccination protect her from the effects of the toxin.
Marie will have a high titer of high-affinity IgG specific for tetanus toxin. This IgG will NEUTRALIZE tetanus toxin by binding to the toxin and will block the toxin’s ability to bind to and enter cells.
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What is a chimeric mAb?
Engineered antibody that has mouse heavy and light chain variable regions but HUMAN CONSTANT regions. Chimeric antibodies are designed to be used therapeutically and to minimize a “human anti-mouse” immune response by the patient.
More recently developed therapeutic mAbs are either “humanized” (only the CDRs are of mouse origin, not the entire V regions) or “fully human” (generally created entirely in the laboratory)
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Describe an antibody effector mechanism by which rituximab can kill lymphoma cells.
IgG antibodies can induce apoptosis via NK-cell mediated ADCC (antibody dependent cellular cytotoxicity).
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How does the CAR differ from a TCR in terms of antigen recognition and signal transduction?
A CAR uses an antibody binding site (an scFv consisting of antibody VH and VL domains) to interact directly with an antigen.
A TCR cannot directly interact with an antigen but binds to a combination of a peptide associated with (bound to) a particular MHC molecule (an allele of an MHC class I or MHC class II)
The TCR complex signals via CD3 plus zeta --> requires signaling via a costimulator molecule such as CD28. A CAR can be engineered so that signaling domains from both CD3 and CD28 are part of the CAR and can activate the T cell.
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By what mechanisms can CAR-T cells kill tumor cells?
CAR-T cells kill by inducing apoptosis of the target cell and use the two normal killing functions of CD8+ T cells: (1) perforin plus granzymes; (2) Fas/FasL interaction.
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What advantage does introducing a CAR into a patient’s T cells compared to introducing a tumor-specific TCR into those T cells?
The CAR uses an antigen-binding site of an antibody that is capable of directly recognizing (and binding) a surface antigen (such as CD19) expressed by the tumor cells.
A CAR specific for CD19 --> can be used by any patient with a CD19+ tumor.
However, every patient expresses unique set of MHC alleles --> using a TCR would require production of a TCR designed for each patient and capable of recognizing a peptide antigen and a particular MHC allele expressed by that patient. (“MHC-restriction”) due to the fact that each individual positively selects (by positive selection during T cell development in the thymus) only those T cells that can recognize that individual’s MHC alleles.
A “custom TCR” would have to be made for each patient based on their MHC (HLA) alleles
