Adaptive Immunity

Question 1

What are the components of adaptive immunity system? What is their function?

Answer 1

cytotoxic T cells (molecular marker CD8)
- eradicate virus or infected and tumour transformed cells

helper T cells (molecular marker CD4)
- antibody production
- removal of bacteria and neutralisation of viruses

B cells (molecular marker CD20)
- differentiate into antibody producing plasma cells with the correct stimulus from helper T cells

Question 2

What is MHC? What is its function?

Answer 2

also known as human leukocyte antigen (HLA)
- complex that allows the body to differentiate between self and non-self, are molecular markers
- displays the antigenic contents of the cell on the cell surface

MHC I - are on all nucleated cells, present products of protein synthesis
MHC II - are only on phagocytic cells, present products that enter the cell via digestion

Question 3

How do T helper cells work?

Answer 3

T helper cells have T cell receptors (TCRs) complexed with a CD4+ molecule
- upon being presented with an antigen-MHC II complex, they bind to it and activate the T helper cell

stimulate B cells by binding to MHC II on their cell surface and releasing cytokines to activate them

activate other immune cells by releasing cytokines
- macrophage and primed cytotoxic T cells

Question 4

How are cytotoxic T cells primed and activated? How do cytotoxic T cell work?

Answer 4

cytotoxic T cells have T cell receptors (TCRs) complexed with CD8+ molecules
- are primed by binding to an APC with an antigen-MHC I via its TCR-CD8+ complex
- are activated by cytokines released by T helper cells

work by releasing cytotoxic granules
- granzymes and perforins

Question 5

How do B cells work? How are they activated?

Answer 5

B cells have B cell receptors (BCRs) that bind antigens
- the antigen is internalised and processed to form a peptide-MHC II that are transported to the cell surface
- activated helper T cells that have the same antigen-MHC II complex bind to the B cell and release cytokines to activate it

activated B cells can divide ad differentiate into plasma cells that produce antibodies and memory cells
- plasma cells divide via clonal expansion

Question 6

What are antibodies? Where are they found?

Answer 6

antibodies are proteins that recognise and bind to antigens with high specificity
- globular glycoproteins

found as
- membrane bound receptors on the surface of B cells
- soluble molecules (secreted from plasma cells)

Question 7

What are epitopes?

Answer 7

antigenic determinant sites
- small part of the antigen interacts with an antibody

Question 8

What is the structure of antibodies and their functions?

Answer 8

consists of 4 polypeptide chains held together by interchain disulphide bridges
- 2 light chains and 2 heavy chains

Fab region
- binds to antigens, are at least two identical sites present on antibodies
- found in the N terminal/variable region

Fc region
- binds to leukocytes/phagocytes
- found in the C terminal/constant region

Question 9

What are the types of antibody responses?

Answer 9

agglutination
- enhances phagocytosis

opsonisation
- enhances phagocytosis

neutralisation
- blocks adhesion of bacteria and viruses

activation of complement
- cell lysis

inflammation

antibody dependent cell-mediated cytotoxicity (ADCC)
- Fc receptor-bearing effector cells can recognize and kill antibody-coated target cells via cell lysis
= typically natural killer cells (NK cells)
- is independent of the immune complement system