Immunology Flashcards
How does the innate system recognize microbes?
Receptors of innate immunity recognize PAMP (pathogen asoociated molecular pattern) on microbes. For example: endotoxin, terminal mannose of glycoproteins, double stranded RNA, unmethylated CpG nucleotides
What are the circulating effector cells?
- neurophils-early phagocytosis and kill microbes
- monocytes/macrophages and dendritic cells-phygocytose and kill microbes, present antigen to T and B cells. Secrete cytokines
- innate lymphoid cells
- NK cells
What is the sequence of events in the migration of blood leukocytes to the site of infection?
Epithelium injury by microbes
1) macrophages and dendritic cells ingest microbes and produce cytokines
2) cytokines activate enothelial cells to produce selectins, ligand for integrins, chemokines
3) neutrophils and monocytes bind weakly to selectin-slows them down
4) integrin ligand on leukocytes roll and encounter and bind to integrins on epithelial cells
5) leukocytes migrate from blood to tissue
6) inflammation
What are dendritic cells?
- Activated by microbes, produce cytokines that activate leukocytes
- Antigen presenting cells
What are innate lymphoid cells?
ILCs-produce effector cytokines
- lack antigen receptor
- regulate inflammatory responses
- e.g. LTi cell produces IL 17, IL22, lymphotoxin, functions in lymphoid tissue dev., immunity to extracellular bacteria
What are natural killer cells? and How are they activated?
- class of lymphocytes
- produces interferon-y(IFN-y), macrophage activating cytokine
- activated by cytokines produced by macrophages, e.g. interleukin-12 (IL-12)
How does the complement system work?
=collection of circulating and membrane associated proteins.
- three pathways
- role in stimulating adaptive immunity by presenting 2nd signal to B cells
How do microbes evade the innate immune system?
- capsules to inhibit phagocytosis
- production of catalase to break down ROS
- resistance to antimicrobial peptide antibiotics
- resistance to complement system
What are examples of cytokines of innate immunity? What is the role of cytokines?
- IFN-y and TGF-beta
- recruit leukocytes to site of infection: inflammation
- activate NK cells (which activate macrophages)
How does innate immunity stimulate adaptive immune responses?
innate immunes response generates 2nd signal which combines with antigen signal to activate T and B lymphocytes
What are some receptors of innate immunity?
Toll-like Receptors (TLR) 1-6. They are expressed in different cellular compartments.
How do Toll like Receptors (TLR) work?
They recruit adapter proteins->recruit and activate protein kinases–>activate transcription factors->gene transcription->expression of different cytokines
What are the components of innate immunity?
Epithelial barriers circulating effector cells dendritic cells innate lymphoid and natural killer cells complement system other plasma proteins
What are some examples of peptides produced by epithelia with naturla antibiotic function?
defensins- in neutrophils graunules
cryptocidins -produced by epithelium of intestine
What are leukocyte adhesion deficiencies?
defects in integrins and selectins causes defective leukocyte recruitment to site of injury–>susceptibility to injury
How do NK cells response when activated?
1) discharge proteins that create holes in plasma membrane of infected cells. Or enter cell and induce apoptosis
2) synthesize IFN-y, activates macrophages to kill microbes
How do normal host cells protect themselves from being attacked by NK?
normal host cells have Self Class I MHC (miajor histocompatibility complex) -inhibitory receptor on NK cells
Cell-mediated immunity vs. humoral immunity
cell mediated: mediated by T lymphocytes, eliminates intra cellular and phagocytosed microbes
humoral: mediated by B lymphocytes, eliminates blood borne microbes, activated by complement system
What kind of microbes do TLR 4 receptor recognize?
gram negative bacterial LPS, fungal mannans, viral envelope protein
How does epithelium prevent microbe entry?
1) physical barrier
2) locally produced antibodies kill microbes
3) intraepithelial lymphocytes kill microbes and infected cels
How do phagocytes ingest and kill microbes?
1) microbes bind to receptors on phagocytes
2) phagocytes zips up around microbe
3) microbe ingested in phagosome
4) phagosome fuses with lysosome
5) microbes killed by lysosomal enzymes and reactive oxygen species (ROS) and nitric oxides (NO)
What is the role of tumor necrosis factor (TNF)?
- a cytokine
- primarily from macrophages and T cells
- activates inflammation in endothelial cells
- activates neutrophils
- causes synthesis of acute phase proteins in liver
- causes apoptosis
What is the role of IL-12?
- a cytokine
- from dendritic cells and macrophages
- affects NK cells and T cells, inducing IFN y production
- T h 1 differentiation?
What does interferon gamma (IFN y) do?
- cytokine
- from NK cells and T lymphocytes
- activates macrophages
- stimulates some antibody response
MHC class I molecules recognize which cells? Where can you find MHC class I expressed?
CD8+CTL T lymphocytes to kill viral infected cells. All cells except RBCs
Which molecules do MHC class II present to? and where can you find MHC class II expressed?
CD4+helper T lymphocytes. Expressed on macrophages, B cells, and professional antigen presenting cells like dendritic cells.
What is the pathway for MHC Class II? I.e. where are peptides acquired and where do MHC bind them?
APCs ingest microbe, microbe in vesicle fused with lysosome. MHC molecules made in ER w/ invariant chain, transported to lysosome, fuses and bind peptides. MHC and peptide transported to cell surface, presented to CD4.
What is the pathway for MHC Class I? I.e. where are peptides acquired and where do MHC bind them?
Microbe in cytosol. Microbial protein unfolded and broken down in cytosol, transported into ER by TAP transporter protein, binds with MHC class I in ER, transported to cell surface to present to CD8.
What is the advantage of restricting T cell recognition to MHC associated peptides?
Means that T cells will only respond to cell associated antigens. MHCs can only be loaded by peptides form inside the cell. T lymphocytes will only respond to antigens that have been phagocytosed and intracellular pathogens.
Describe the structure of an antibody.
Two heavy chains and two light chains. Light chain has 1 V and 1 C domain, heavy chain has 1 V and 3 C domains. IgG is most common Ig, and can be separated into Fab and Fc fragments.
Describe TCR structure.
Has a alpha and beta chain, each with a V and C domain.
What are the mechanisms that generate diversity in Ig and TCR antigen receptors?
1) Multiple Vh/Vl and Valpha/Vbeta gene segments
2) somatic recombination of VDJ and VJ joining
3) random assortment of heavy and light or Valpha and Vbeta chains
4) junctional diversity
What is junctional diversity?
At the junctions of V (D) and J gene segments, TdT enzyme may add nucleotides and and an exonuclease may remove nucleotides. The ends are ligased together, but joining is imprecise.
What are the main characteristics of IgG?
- most abundant, long lived
- in blood and tissue?
- crosses placenta to protect fetus
- neutralizes bacterial toxins and viruses
- activates complement
- binds to pathogens to enhance phagocytosis
What are the main characteristics of IgM?
- First antibody in humoral immune response
- pentamers, low affinity, high avidity
- mostly in blood
- activates complement
What are the main characteristics of IgA?
- SECRETIONS, mucosal surfaces like intestinal, respiratory,
- forms dimers
What are the main characteristics of IgD?
- coexpressed with IgM
- secreted in upper respiratory mucosa
- involved in lymphocyte activation and suppression
What are the main characteristics of IgE?
- Monomer, looks like IgM
- low concentration in serum
- Allergic rxns and protection against parasites: binds to mast cells, antigen binding triggers degranulation and release of inflammatory mediators
- sensitizes for killing by eosinophils
What is class switching?
Allows IgM to switch to a different heavy chain isotope class
What is the mechanism of class switching?
- B cell starts with IgM expressed
- signals stimulate transcription of C region downstream of C(mu)
- switch regions rich in G-C that are targets of AID and DNA machinery mediates DNA rearrangement
How is isotype switching different from VDJ rearrangement?
- after antigen binds
- always productive
- regulated by T cells, not random
What is a cross reaction?
the binding of an antibody to an antigen other than the immunogen (any molecule that can elicit a specific immune response)
What is somatic hypermutation?
point mutations introduced into V regions of rearranged heavy and light chain genes at very high rates after antigen exposure–>affinity maturation. Occurs in germinal centers of lymph nodes.
What is affinity maturation?
Affinity of antibodies for protein antigens increases with repeated exposure to antigen. when mutant Ig molecules bind antigens better than original surface Ig, and the B cells are selected to mature into plasma cells.
What happens in the maturation stages of T lymphocytes?
T cells progenitors go from bone marrow to thymus. 1) express CD3 2)rearrange beta chain 3) rearrange alpha chain 4) exit thymus as CD4 or CD 8
How does positive and negative selection occur in T lymphocytes?
Positive: T cells interact with class I or II, weak recognition. Failure of positive selection-->death by neglect if no recognition of MHC negative: T cells interact too strongly with class I or II-->death
What are the stages of B cell development?
1)pro-B: H chain rearrangement.
2)pre-B: light chain rearrangement
3)immature B: rearragement ceases, expresses IgM
4)mature B: express IgM and IgD
At pro B and pre B stages, if rearrangement leads to failure to express either H chain or Light chain, it results in cell death.
What is allelic exclusion?
Only one Ig antigen receptor, only one of two parental alleles of Ig is expressed. Same is true for beta chain of TCR.
How do B cells undergo selection during maturation?
Negative: if immature B cells react strongly with self antigens in bone marrow, they die or change receptor specificity
-only small fraction mature and survive in peripheral lymphoid tissues
How are monoclonal antibodies made?
- B cells that secrete Ab of interest, can grow in HAT medium
- mouse/other myeloma cell line that can grow indefinitely in culture and cannot grow in HAT. Doesn’t secret Ab
- Fused, hybridomas secret Ab and can grow in HAT.
How are agglutination and precipitation reactions used ?
agglutination: large particle displays antigen causes clumping. Determine blood group
precipitation: Ab and Ag added in fixed ants, crosslinking occurs, precipates, confirms Ab presence
How do B cells undergo selection during maturation?
Negative: if immature B cells react strongly with self antigens in bone marrow, they die or change receptor specificity
-only small fraction mature and survive in peripheral lymphoid tissues
How are monoclonal antibodies made?
- B cells that secrete Ab of interest, can grow in HAT medium
- mouse/other myeloma cell line that can grow indefinitely in culture and cannot grow in HAT. Doesn’t secret Ab
- Fused, hybridomas secret Ab and can grow in HAT.
How are agglutination and precipitation reactions used ?
agglutination: large particle displays antigen causes clumping. Determine blood group
precipitation: Ab and Ag added in fixed ants, crosslinking occurs, precipates, confirms Ab presence
What is ELISA?
- quantitate antigen
- antigen attached to wells, binding of antibody detected by rxn with antibody labelled enzyme that changes colors on binding
What is western blotting?
- detects protein in mixture
- SDS separate proteins
- blotted to nitrocellulose
- label with specific antibody
- detect antibody
What is fluorescent activated cell sorting FACS?
machine that can measure cell size, granularity, fluorescence bound Ab
What are the signals that induce B cell responses to protein antigens?
- Require two responses
1) antigen binding to antigen receptor
2) C3d complement
What are the signals that induce B cell responses to polysaccharide antigens?
-often have multiple identical epitopes that can cross link many Ig receptors, providing adequate signals for B cells without helper T cell activation.
How do helper T cells specific for an antigen interact with B lymphocytes specific for the same antigen?
- protein antigen activates CD4 helper T cells
- B lymphocytes (internalize specific antigen) present class II MHC peptides to helper T cells specific for the antigen
- helper T express CD40L +secrete cytokines–>B cell proliferation and differentiation
Where do helper T cells and B lymphocytes interact?
Edges of Lymphoid follicle
What are the mechanisms by which helper T cells stimulate B cell proliferation and differentiation?
- T cell expresses CD40L+ secrete cytokines that activate B cells
- CD40L mediates signals for class switching
What is the first step in B cell activation?
-clustering of antigen receptors Ig alpha and beta. Become docking sites for adapter proteins and the beginning of signaling cascade that increases transcription of genes involved in B cell proliferation
What occurs within germinal centers?
- B cells undergo V region somatic mutation
- affinity maturation, aided by antigen presented by follicular dendritic cells
- memory b cells develop
- proliferation of b cells
What is hyper IgM immunodeficiency?
-Individuals lac CD40L and cannot induce class switching. Produce elevated IgM and little IgG
How is the antibody response shut down?
-Antibody feedback mechanism: secreted antibodies form immune complexes with residual antigen and shut off B cell activation by engaging inhibitory Fc receptor on B cells
What does the Th1 subset class do?
stimulate phagocyte mediated ingestion and killing of microbes.
-Produces INF-y (activates macrophages). -Differentiates under influence of Il-12 produced by macrophages and dendritic cells.
What does the Th2 subset class do?
- produce Il-4. Stimulates production of IgE antibodies.
- Also Il-5, activates eosinophils. Effective against helminthic parasites.
- Differentiates under influence of Il-4.
- -Il-4, Il-10, Il-13 inhibit macrophage activity and suppress Th1
What do Th17 cells do?
Host defense against fungi, bacteria, organ-specific autoimmune disease. Produces by Il-17
What are regulatory T cells? (Tregs)
- develop from CD4 cells exposed to persistent antigen in periphery
- secretes immune suppressive cytokines (TGF b, Il-10, Il-35)
- inactivates dendritic cells or responding lymphocytes
- FoxP3+ CD4+CD25+
Deficiencies in C5-C8 complement are susceptible to what infections?
Neisseria
What are the outcomes of complement activation?
1) Opsonization and phagocytosis
2) lysis of microorganisms by MAC
3) initiation of local inflammation response by C3a and C5a
What C3b receptor on phagocytic cells aid in phagocyte ingestion?
CR1, expressed on phagocytes and erythrocytes
Individuals deficient in C3 complement suffer from infections with?
pyogenic and gram negative bacteria
Deficiences in C1, C2, and C4 are associated with what?
autoimmune diseases
What serum pproteins are inhibitors of complement activation?
Factor H and I
Hereditary angioneurotic edema is due to deficiency in what enzyme?
C1 esterase. Action of C1 on C4 and C2 is uncontrolled–>vasoactive peptides
What proteins do host cells express that inhibit inadvertent activation of complement?
- DAF decay acelerating factor-displaces Bb from C3b and C2b from C4b
- CD59 prevents the formation of MAC
Deficiency in DAF or CD59 and result in what disorder?
paroxysmal nocturnal hemoglobulinuria
What are the effector functions of antibodies?
1) neutralization of bacterial toxins, viruses, and bacteria
2) opsonization to enhance phagocytosis of bacteria by macrophages and neutrophils
3) activation of complement
What is Il-4 responsible for?
- B cell activation and growth
- IgE class switching
What is Il-5 responsible for?
Eosinophil growth
Which vaccines are live attenuated?
- Sabin polio
- MMR
- Varicella-Zoster
Which vaccines are inactivated?
- DTap-diphteheria, tetanus, pertussis
- Salk polio
Which vaccines are conjugated?
H. influenzae, type B (HiB)
Strep pneumonia
Neisseria meningitidis
Which vaccines are subunit vaccines?
Hep B
What is an example of passive immunity or antiserum?
Mom transferring IgG across placenta or breast milk to baby
What adhesion molecules are important in facilitating the entry of naive B and T cells into lymphoid organs via high endothelial venules?
CCR7 and L selectin CD62L
How are Mast cells activated?
- IgE binds mast cell via Fc(epsilon)RI receptor
- Mast cell degranulates and releases histamine and heparin
Which pathogens affect B cells?
- RNA viruses
- encapsulated organisms
- Giardia
What pathogens affect T cells?
- DNA viruses
- TB and atypical bacteria
- fungal
- protozoal
How to microbes resist phagocytosis? What’s an example?
Capsular polysaccharide. Pneumococcus
How to microbes resist ROS? What’s an example?
Produce catalase. Staphylococci
How to microbes resist complement activation? What’s an example?
In neisseria, sialic acid inhibits C3 and C5 convertase. In streptococcus, M protein blocks C3 binding to microbe and C3b binding to complement receptors
How to microbes resist peptide antibiotics? What’s an example?
Synthesize modified LPS that resist action of peptide antibiotics. Pseudomonas.
