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POM 4: Immunity and Infection > 7: Lymphocytes > Flashcards

7: Lymphocytes Flashcards

Adaptive immunity, immune memory, antigen receptor diversity, T cells, MHC, B cells, antibody function

1
Q

Adaptive immunity

A

response of vertebrate immune system to a specific antigen that typically generates immunological memory

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2
Q

Cells involved in adaptive immunity

A

B cells
Antibodies
T cells
Natural killer T cell (also in innate immunity)

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3
Q

An adaptive immune response (AIR) is initiated when

A

a pathogen overwhelms innate defence mechanisms
pathogen replicates, antigen accumulates = sensor cells become activated to trigger AIR
Expansion of antigen-specific lymphocytes that target pathogen specifically, formation of memory cells providing long-lasting specific immunity

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4
Q

Role of adaptive immune system

A
  • Improves efficacy of innate immune system
  • Focuses a response on site of infection and organism responsible
  • has memory
  • needs time to develop
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5
Q

What major event occurs in peripheral lymphoid tissues to initiate adaptive immune responsse?

A

B or T lymphocytes encounter antigens for which receptors have specific reactivity

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6
Q

Antigen

A

molecules recognised by highly specialised lymphocyte receptors, which act to induce an adaptive immune response

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7
Q

2 hallmarks of adaptive immune response

A
  • Creates immunological memory; long-lasting protection
  • Highly specific : recognises non-self antigens
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8
Q

Issue with Specificity

A

antigen diversity - large number of lymphocyte receptors that can recognise array of antigens needed
10^15 different antibody/BCR molecules can be generated each coded by one gene = this isnt possible so immunoglobulin gene rearrangement occurs

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9
Q

Immunoglobulin gene rearrangement

A

Each BCR receptor chain encoded by separate multigene families on different chromosomes
During B cell maturation, gene segments rearranged and brought together

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10
Q

How is diversity generated overall?

A

Germline diversity
Combinatorial diversity
Junctional diversity
Heavy + light chain diversity

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11
Q

Germline diversity

A

Each gene segment consists of different base sequence

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12
Q

Combinatorial diversity

A

formation of different combinations of V, J and D segments from each cluster

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13
Q

Junctional diversity

A

addition/removal of random bases to form a viable junction between selected V, D and J segments

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14
Q

Heavy+light chain diversity

A

same heavy chain can be combined with different versions of a light chain (and vice versa)- many different combinations of heavy and light chain V regions that pair to form antigen-binding site in immunoglobulin molecule

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15
Q

Issues with the process of gene rearrangement

A

with many different receptors generated randomly during lifetime, possibility of self-reactive antibodies –> autoimmunity

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16
Q

Immunological memory

A

quicker response, producing antibodies

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17
Q

T cell response

A

Cell-mediated response

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18
Q

B cell response

A

Humoral/antibody response

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19
Q

Lymph node interactions of B cells

A

stay outside lymph node
- respond directly to antigens drained into the lymph node

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20
Q

Lymph node interactions of T cells

A

Interior to lymph node

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21
Q

3 Types of T cells

A

Antigen binds to receptor - cell proliferates and differentiates into :
Cytotoxic T cells
Helper T cells
Regulatory T cells

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22
Q

Cytotoxic T cells

A

kill infected cells or other intracellular pathogens bearing the antigen

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23
Q

Helper T cells

A

provide signals (specific cytokines) that activate other cell functions e.g B cell antibody production / macrophage killing engulfed pathogens

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24
Q

Regulatory T cells

A

suppress other lymphocyte activity
help limit possible damage of immune response

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25
What molecule on T cell surface helps distinguish T helper and T killer cells
CD4 - helper CD8- killer
26
Types of Th cells
Tfh Th1 Th17 Th2 Treg (Th0)
27
Tfh cells
pro-antibody B-cell support Produce : IL-21
28
Th1 cells
pro-inflammatory boost cellular immune response- produce interleukins that promote B cell class switching involved in macrophages and inflammation Produce: Interferon Gamma, Tumour Necrosis Factor, IL-12
29
Th17 cells
pro-inflammatory control bacterial and fungal infection, neutrophils Produce: IL-17, IL-23, IL-6
30
Th2 cells
pro-allergic involved in allergies and worms (parasites) Boost multicellular response Produce: IL-4,IL-5, IL-13
31
Treg (Th0) cells
anti-inflammatory limit immune response /supress T cell response Produce: IL-10, TGFbeta
32
By what pathway do T helper cells activate B cells
thymus dependent pathway - release of cytokines cause B cell proliferation and differentiation (clonal selection + expansion) into plasma and memory B cells
33
How do CD8 T cells kill pathogens?
Release perforins and granzymes
34
How do CTLs initiate programmed cell death?
Cytotoxic T cells (CTL) kill targets by apoptosis (characterised by fragmentation of nuclear DNA) CTL store perforin, granzymes, granulysin in cytotoxic granules- released after target recognition Perforin molecules polymerise, form pores
35
Two ways T cells recognise foreign antigens
Interactions between MHC and T-cell receptors
36
Epitope / antigenic determinant
region recognised by T cell antigen receptor - antigen broken down into peptide fragments -epitope peptide binds to self molecule and MHC molecule -T cell receptor binds to complex of MHC molecule and epitope peptide
37
Epitope is formed by
combination of MHC-II and part of antigenic protein
38
MHC stands for
Major Histocompatility Complex
39
Role of MHC
Recognises self and non-self APC takes in foreign peptides and forms MHC, which allows for T cell selection
40
What is the difference between MHC-I and MHC-II
MHC-1 : all nucleated cells, single variable alpha chain and common B-microglobulin MHC-2 : only on "professional" antigen presenting cells e.g Dendritic cells, macrophages, B lymphocytes has 2 chains, alpha and beta
41
Describe the structure of MHC class I molecules
Consist of two polypeptide chains An alpha chain noncovalently associated with smaller chain, B2-microglobulin Complete MHCI has 4 domains, 3 formed from MHC-encoded alpha chain, one from B2-microglobulin Folded a1 and a2 domains form walls of cleft on surface of molecule = peptide-binding cleft/groove MHC molecules are highly polymorphic - major differences in allelic forms located in cleft= influences peptide binding
42
Describe the structure of MHC-II molecules
consists of a noncovalent complex of two chains, a and b both of which span membrane peptide-binding cleft is formed by two domains from different chains, a1 and B1 domains sites of major polymorphism in MHCII molecules located in peptide-binding cleft
43
How does MHCI interact with T cell receptors
Intracellular pathogen/antigen presented on MHCI binds to CD8 T cells in cytosol CD8 cytotoxic T cell responsible for pathogen surveillance and cytolysis of somatic cells
44
How does MHCII interact with T cell receptors
Extracellular pathogen/antigen presented on MHCII binds to CD4 T cells in endosomes CD4 cells differentiate into several subsets of effector T cells that have different immune functions
45
Process of MHCI recognition
1. Virus infects cell 2. Viral proteins synthesized in cytosol 3. Peptide fragments of viral proteins bound by MHCI in ER 4. Bound peptides transported by MHCI to cell surface 5. Cytotoxic T cells recognise complex of viral peptide with MHCI and kills infected cell
46
How is MHC expressed
co-dominant expression each person can have up to 6 of each gene if completely heterozygous more than 17,000 MHC variants
47
Two properties of MHC making it difficult for pathogens to evade immune response
MHC is polygenic - several different MHCI and MHCII genes, so every person has a set of MHC molecules with different ranges of peptide-binding specificities MHC is highly polymorphic - multiple variants/alleles of each gene within whole population
48
B cell antigen receptors
BCR - surface bound antibody - encodes antibody the cell will make
49
BCR region of B cell
unique binding site which binds to antigenic determinant / epitope of antigen Made before cell ever encounters antigen Present in 1000s of identical copies on B cell surface
50
Two pathways by which antibody production by B cells is achieved
Thymus-dependent pathway Thymus-independent pathway
51
Thymus dependent pathway
- membrane bound BCR recognises (thymus dependent) antigen - receptor-bound antigen is internalised and degraded into peptides -peptides associate with "self" molecules (MHC-2) and is expressed at cell surface - Complex recognised by matched CD4 T helper cell - B cell activated (class switched, mature plasma/memory cell)
52
Thymus independent pathway
-some microbial antigens (thymus-independent antigens) activate B cells, in absence of helper T cells -second signal triggered from direct recognition of common microbial constituent (LPS) = activating TLR signalling in B cell -only IgM ; no memory produced
53
Thymus-independent antigens
highly repetitive molecules can cross-link the BCR on B cells e.g polysaccharides of bacterial cell walls
54
What happens once B cells undergo clonal selection
clonal expansion
55
Describe what is meant by clonal expansion of lymphocytes
1.foreign antigen interacts with receptor on mature naive lymphocyte, cell activated and divides 2. undergoes clonal expansion 3. antigen specificity maintained as cloned cells proliferate and differentiate into effector cells
56
5 types of antibodies produced by B cells
IgM IgG IgA IgE IgD
57
What is antibody type and function defined by
structure of its heavy chain
58
IgG
\\// || Highest opsonisation and neutralisation acrivities Classified into four subclasses - IgG1/2/3/4 lymphatic system
59
IgM
(5 Y star structure) produced first upon antigen invasion, increase transiently lymphatic system
60
IgA
(Two or 3 star Y structure) expressed in mucosal tissues forms dimers after secretion small intestine, mouth, oesophagus
61
IgD
\\// || unknown function lymphatic system
62
IgE
\\// || || Involved in allergy lymphatic system
63
Fab region of antibody
antibody region - varies between antibody types
64
Fc region of antibody
constant region
65
Describe the structure of the IgG antibody
Two heavy chains and two light chains two heavy chains linked by disulphide bonds, each heavy chain linked to light chain by disulphide bond Two identical antigen-binding sites Two types of light chains, lambda and kappa, found in antibodies (never one of each)
66
3 core functions of antibodies
Neutralisation Opsonisation Complement activation
67
Neutralisation
antibodies bind to viruses/bacterial toxins and block access to cell they might infect or destroy
68
Opsonisation
antibodies coat bacterium to better enable phagocytic cells e.g macrophage/neutrophil to ingest and destroy it (Fc receptor on phagocytic cell binds to C receptor)
69
Complement activ
antibodies coat bacterial cell; C regions form platform that more efficiently activate complement proteins (covalent deposition on bacterial surface)--> complement proteins on bacterium can be recognised by complement receptors on phagocytes; stimulates phagocytes to ingest and destroy the bacterium

POM 4: Immunity and Infection (9 decks)

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