Antigens and Antigen Presentation

Question 1

Factors affecting immunogenicity of antigens

Answer 1

Foreignness, size, chemical composition (more complex = more immunogenic), physical properties (particulate > soluble, denatured > native), degradability (easily degradable = highly immunogenic), genetic factors, age, chemical properties (proteins vs polysaccharides vs NAs vs lipids)

Question 2

T-independent antigens

Answer 2

bypass T cells and directly stimulate B cells to produce antibodies. TIAs have a polymeric structure, with the same antigenic determinant being repeated, may activate lymphocytes polyclonally and are resistant to degradation.
No class switching, no memory

Question 3

T-dependent antigens

Answer 3

indirectly stimulate B cells to produce antibodies (use T cells to stimulate). Most often these antigens are proteins. Contain a few copies of various antigenic determinants

Question 4

Superantigens

Answer 4

Activate many lymphocytes at once (non specific). Mostly from bacteria or viruses. Bind to the variable domain of the TCR of CD4+ cells and to the alpha MHC II chain
This induces a strong signal that activates many T cells polyclonally. Could lead to system toxicity

Question 5

DC antigen presentation

Answer 5

to naive CD4 or 8 T cells to initiate T cell response

Question 6

Macrophage antigen presentation

Answer 6

present to differentiated CD4+ T cells in the effector phase of cell-mediated immunity

Question 7

B lymphocyte antigen presentation

Answer 7

to T helper cells during humoral response

Question 8

2 important functions of APCs

Answer 8

1. capture, process and present peptides with MHC

2. provide co-stimulation to t cells

Question 9

How are endocytosed antigens processed?

Answer 9

1. extracellular proteins will be uptaken into vesicular compartments
2. proteins will be internalized in endosomes and lysosomes
3. transport of MHC II to endosome
4. association of MHC II with peptides in endosome
5. expression of MHC II-peptide on cell surface

Question 10

what are cathepsins

Answer 10

the most important proteolytic enzyme involved in protein degradation for antigen presentation

Question 11

Biosynthesis of MHC

Answer 11

1. alpha and beta chains are formed in the ER and then sent to the golgi
2. In the golgi, invariant chain is attached and then MHC is sent to endosomes
3. Once in endosomes, invariant chain dissociates so MHC II can bind to antigen

Question 12

Processing of cytosolic antigens for MHC I

Answer 12

1. cytosol location of foreign protein
2. proteolytic degradation in proteasome
3. transport of peptides from the cytosol to the ER
4. assembly of peptide MHC-I in the ER
5. Surface expression of peptide MHC-1

Question 13

what is TAP?

Answer 13

TAP is the molecule that transports antigens from the proteasome to the ER

Question 14

Where is the alpha-beta TCR typically found?

Answer 14

T cells in lymph tissues

Question 15

Where is the gamma-delta TCR typically found?

Answer 15

T lymphocytes, mucosal surfaces

Question 16

Alternative method of lipid antigen presentation

Answer 16

Lipid antigens can be presented through CD1, also found on APCs and some epithelial cells. CD1s present antigens to T cells that are not MHC-restricted (ex: NKT cells)

Question 17

T cell costimulation

Answer 17

Signal 1: due to binding of MHC to TCR-CD3 complex. (survival signal)
Signal 2: from binding of CD28 on T cells to B7 (CD80/86) on APCs (proliferate signal)

Question 18

Clonal anergy

Answer 18

occurs when T cells do not receive proper co-stimulation. Leads to T cells that are unresponsive

Question 19

How does recognition of microbial products by TLRs affect APCs

Answer 19

This will induce upregulation of MHC expression and co-stimulation molecules. Improves antigen presentation efficiency, stimulates chemokine production

Question 20

DC properties that make them very effective for initiating T cell response

Answer 20

DCs are strategically located at common microbe sites of entry
DCs express receptors that allow them to capture and respond to microbe
DCs preferentially migrate to T-cell-rich zones of lymph nodes
Mature DCs express lots of costimulatory molecules
DCs can ingest infected/tumour cells and present to CD8 cells (cross-presentation)