Lymphocytes

Question 1

How do T cells and B cells recognise antigens?

Answer 1

T cells recognise linear epitopes in MHC class 1 or 2
B cells and antibodies recognise structural epitopes

Question 2

Immunoglobulin gene rearrangement?

Answer 2

During B cell maturation these gene segments are rearranged and brought together so the BCR receptor chains have different shapes

Question 3

MHCI vs MHCII

Answer 3

Class I is in all nucleated cells and has a single variable alpha chain and a common beta-microglobulin
Class II is normally on APCs and has an alpha and beta chain

Question 4

What is MHC coded by?

Answer 4

HLA genes, polygenic and co-dominant so can have upto 6 genes

Question 5

Intracellular vs extracellular pathogens processed, presented on and to?

Answer 5

Cytosol, MHCI, CD8 T cells vs Endosomes, MHCII, CD4 cells

Question 6

What do CD4 cells release?

Answer 6

cytokines

Question 7

5 classes of CD4 cells?

Answer 7

Treg (Th0)
Th1- pro inflammatory and boosts cellular response
Th2- pro allergic
Th17- pro inflammatory and control bacterial and fungal infections
Tfh- pro antibody

Question 8

How do CD8 cells kill infected cells?

Answer 8

Activate apoptosis. They store perforin, granzymes and granulysin in cytotoxic granules

Question 9

5 stages of CD8 attack mechanism?

Answer 9

1. In uninfected cells, MCH I molecules show self peptides
2. Infected cells make viral proteins
3. Non self MHC displayed
4. CD8 cells detect non self MHC and attack
5. Infected cell killed

Question 10

6 features of antibody structure?

Answer 10

2 heavy, 2 light, 1 variable and 1 constant region

Question 11

3 protective roles of antibodies

Answer 11

Neutralisation
Opsonisation
Complement activation

Question 12

5 classes of antibodies and their functions?

Answer 12

IgG- opsonisation and neutralisation, 4 subclasses
IgM- produced first upon antigen invasion
IgA- expressed in mucosal tissues, forms dimers
IgD- unknown function
IgE- involved in type 1 hypersensitivity

Question 13

How are naive B cells activated?

Answer 13

By an antigen plus an accessory signal from either the pathogen or a T helper cell

Question 14

Microbial constituents, thymus independent pathway?

Answer 14

Often a polysaccharide, e.g bacterial surface sugars

Second signal is provided by a microbial PAMP, e.g LPS

Question 15

T helper cell, thymus dependent pathway?

Answer 15

Membrane bound BCR recognises antigen
Receptor bound antigen is internalised and degraded
Peptides are expressed on MHC Class II at cell surface
Complex recognised by matched CD4 T helper cells
B cell is activated