Lymphocytes (15)

Question 1

What is the purpose of adaptive immunity?

Answer 1

• improves efficacy of innate immune response
• focuses response of site of infection and specific organism
• has memory

Question 2

What are the 2 types of adaptive immune response?

Answer 2

• humoral: B cells and antibodies

- cell mediated: T cells and cytokines and killing

Question 3

What is an antigen?

Answer 3

molecule that induces an adaptive immune response

Question 4

What is an epitope?

Answer 4

the region of an antigen that receptors bind to

Question 5

What is clonal selection?

Answer 5

• each lymphocyte has a unique receptor
• interaction between a foreign molecule and its receptor leads to activation
• cell will differentiate and multiply into many of this cell
  ^clonal expansion

Question 6

How is antigen receptor diversity generated?

Answer 6

• we encode a massive repertoire

- gene recombination (VDJ)

Question 7

What do T cell receptors recognise?

Answer 7

linear epitopes (fragments of proteins/antigens) presented by MHC molecules

Question 8

What is the major histocompatibility complex (MHC)?

Answer 8

• protein complex encoded by HLA genes in humans
• presents antigens to T cells
• polygenic: several class 1 and 2 loci
• codominant expression (maternal/paternal)

Question 9

What is the difference between MHC1 and MHC2?

Answer 9

• class 1: on all nucleated cells…constantly present proteins made in cell on surface…communicates w/ CD8 T cells
• class 2: on specific antigen-presenting cells esp. dendritic cells…engulf pathogen and present fragments…communicates w/ CD4 T cells

Question 10

What are the 2 types of T cell?

Answer 10

• helper: CD4 surface molecules

- killer: CD8 surface molecules

Question 11

What is the function of CD8 T cells?

Answer 11

• MHC1 recognises non-self
• perforin punctures holes in cell and granzyme injected–> drives apoptosis
• kill cells by programmed cell death/apoptosis

Question 12

What is the function of CD4 T cells?

Answer 12

produce cytokines to influence outcome of immune response

Question 13

What is the structure of an antibody?

Answer 13

• variable region: gives specificity for binding antigen
• constant region
• four polypeptides: two heavy chains and two light chains

Question 14

What are the 5 classes of antibody?

Answer 14

IgG standard in blood
IgA mucosal
IgE allergy
IgM nonspecific

Question 15

What are the 3 core protective roles of antibodies?

Answer 15

1. neutralisation: bind pathogen and prevent adherence to cells
2. opsonisation: mark pathogens to promote phagocytosis
3. complement activation: enhances opsonisation and lyses some bacteria

Question 16

Where does B cell generation and maturation occur?

Answer 16

progenitor B cell matures in bone marrow in absence of antigen into mature B cell w/ single receptor (BCR= surface bound antibody–> encodes antibody the cell will make)

Question 17

What are the 2 pathways by which antibody production is achieved in B cells?

Answer 17

Thymus-independent:

• only make IgM (so no class switching)
• no memory
• B cell directly activated by repetitive microbial constituents (e.g. polysaccharide) w/out help of T cells

Thymus-dependent:
- makes all Ig-classes
- memory
- B cell activated when it expresses pathogen’s peptides w/ MHCII on surface and a matched CD4 T helper cell recognises this complex
(N.B. dendritic cell allows Th cell to be activated)