L1 - Acquired immunity: Ag recognition systems

Question 1

What are the sources of infection?

Answer 1

Pathogens

Question 2

What are pathogens?

Answer 2

Organisms that cause disease 
• Bacteria 
• Viruses 
• Fungi 
• Parasites

Question 3

What must the immune system be able to do for an effective immune response?

Answer 3

Be able to recognise & respond to any invading organism

Not over react to benign or self

Be able to direct different effector mechanisms against different pathogens

Question 4

Difference between innate & adaptive immunity?

Answer 4

Innate is activated very quickly

Adaptive takes over if innate doesn’t completely control the pathogen

Question 5

Specific/adaptive immunity

Answer 5

Induced by exposure to a particular infection

Shows a high degree of specificity

Exhibits memory

Question 6

Features of specific immunity

Answer 6

Clonally distributed receptors

Large repertoire

Response takes time to develop

Memory cells produced

Question 7

Clonal selection

Answer 7

1. Removal of potentially self-reactive immature lymphocytes by clonal deletion
2. Pool of mature naïve lymphocytes
3. Proliferation & differentiation of activated specific lymphocytes to form a clone of effector cells

Followed by clonal expansion

Question 8

What are the 2 lymphocyte receptors for antigens?

Answer 8

B lymphocytes

T lymphocytes

Question 9

B lymphocytes

Answer 9

BCR expressed by B cells

Membrane anchored protein on the surface of B cell

Binds free antigen

Is subsequently secreted with B cell is activated = an antibody

Question 10

T lymphocytes

Answer 10

TCR expressed by T cells

Membrane form only - stays on the surface where it functions

Recognises a peptide fragment of antigen bound to MHC expressed by APCs

Question 11

What do antibodies do?

Answer 11

Activation of complement

Activation of effector cells

Question 12

What are antibodies formed of?

Answer 12

Formed of 4 polypeptides
• 2 heavy chains & 2 light chains

Formed by domains - variable & constant

Held together by covalent & non-covalent bonds

Question 13

What do the variable & constant regions do?

Answer 13

Variable regions form the antigen-binding sites - specific for a given Ab

Constant regions are responsible for antibody structure & interacting with other molecules

Question 14

What are the 2 types of light chain?

Answer 14

Lambda and Kappa

Question 15

What are the 5 classes of antibody?

Answer 15

IgM, A, D, G, E

Isotype determined by the heavy chain

Differ in structure & function

Question 16

What are epitopes?

Answer 16

The part of an antigen molecule to which an antibody attaches itself

Question 17

What are the 2 types of epitope?

Answer 17

Continuous

Discontinuous/conformational

Question 18

TCRs

Answer 18

Binds/recognises processed antigens (peptides)

Heterodimer of alpha & beta chain (sometimes gamma & delta)

Each chain has a V & C region

Each chain contributes 3 CDRs to Ag binding

Question 19

What are CDRs?

Answer 19

Complementarity-determining regions (CDRs)

Part of the variable chains in immunoglobulins (antibodies) and T cell receptors, where these molecules bind to their specific antigen

Question 20

What are MHC?

Answer 20

Major Histocompatibility Complex molecules

Type I or II - related but different structures

Question 21

Class I MHC

Answer 21

Expressed on all nucleated cells

Heterodimer – 3 alpha chains & beta2-microglobulin

Alpha1 & alpha2 domains fold to form beta-sheet structure known as the peptide binding site (groove/cleft)

Alpha3 & beta2-microglobulin fold into Ig-like domains

Question 22

What are the 3 different MHC I molecules?

Answer 22

HLA-A
HLA-B
HLA-C

Encoded by separate alpha chain genes
A single gene encodes beta2-microglobulin so same in all 3

Question 23

Class II MHC

Answer 23

Expression limited to APC (& cytokine-activated cells)

Heterodimers – 2 alpha & 2 beta chains & both transmembrane

Alpha & beta chains encoded by separate genes encoded within MHC

Both alpha2 & beta2 domains are Ig-like

Polymorphic alpha1 & beta1 domains form peptide binding sites

Question 24

What are the 3 different MHC II molecules?

Answer 24

HLA-DP
HLA-DQ
HLA-DR

Question 25

What makes up the peptide binding site in MHC I?

Answer 25

Alpha1

Alpha2

Question 26

What makes up the peptide binding site in MHC II?

Answer 26

Alpha1

Beta1

Question 27

What makes up the Ig-like domain in MHC I?

Answer 27

Alpha3

Beta2-microglobulin

Question 28

What makes up the Ig-like domain in MHC II?

Answer 28

Alpha2

Beta2

Question 29

A TCR expressed by a T cell that co-expresses CD8 can bind what MHC?

Answer 29

Class I MHC

Question 30

A TCR expressed by a T cell that co-expresses CD4 can bind what MHC?

Answer 30

Class II MHC

Question 31

MHC I binds what length peptides?

Answer 31

Binds peptide 8-10 AA to present to TCR

Question 32

MHC II binds what length peptides?

Answer 32

Binds peptide 13+ aa to present to TCR

Question 33

Define the Fab and the Fc regions of an antibody?

Answer 33

Fab - fragment antigen binding
Region on an antibody that binds to antigens

Fc - fragment crystallizable
Tail region of an antibody that interacts with cell surface receptors

Question 34

The Lamda and Kappa chains form the …. chain of an antibody?

Answer 34

Light chain

Question 35

Does beta 2 microglobulin bind to the processed peptide?

Answer 35

No

Question 36

How many transmembrane domains does an MHC class I and an MHC class II molecule have respectively?

Answer 36

MHC I - 1 transmembrane domain

MHC II - 2 transmembrane domains

Question 37

What does HLA stand for?

Answer 37

Human Leukocyte Antigen