Antigens-Thrush

Question 1

What is an antigen? What do antigens bind to in order to illicit a response?

Answer 1

any molecule that can interact with the products of the immune response
Antigens bind to antibodies or T cell receptors

Question 2

What are the 3 major categories of antigens? What is the most common antigen that stimulates the immune response?

Answer 2

1. autoantigen- a self antigen
2. alloantigen=an antigenic difference within a species
3. xenoantigen-an antigenic difference between species. xenoantigens are the most common activators of the immune response.

Question 3

What does it mean to describe an antigen as immunogenic? What are the most common immunogens?

Answer 3

immunogenic: ability to induce an Ab (antibody) and/or a CMI (cell mediated immunity) response on it’s own
Proteins are the most potent immunogens, then polysaccharides. Lipids and nucleic acids are NOT usually immunogenic (even though they are antigenic)

Question 4

What antigen features make good immunogens?

Answer 4

1. foreignness (greater differences from our self antigens)
2. molecular size (larger is better >100,000 Daltons)
3. chemical composition (more complex=better)
4. susceptibility to antigen processing/presentation (D-amino acids are not degraded and L-amino acids are–> necessary for T cell response)

Question 5

What is a hapten? How can they be modified to become immunogenic?

Answer 5

haptens – small molecules that are antigenic but not immunogenic

often need to be attached to a carrier (protein) to become immunogenic
Ex.: penicillin, catechol

Question 6

Where are the epitopes for B cells and T cells located on the antigen? Are the epitopes for T cells and B cells sequential or non-sequential? What additional features are necessary for T cells to recognize epitopes?

Answer 6

B cells recognize external epitopes that can be either sequential or non-sequential and normally 8-22 AAs.

T cells recognize epitopes can be anywhere in protein (including internal) that are sequential. These range from 8-10 AA for CD8+ cells to 13-18 AAs for CD4+ cells.

The T cells also require that the antigen interact with TCR (T cell receptor) and MHC.

Question 7

What is a mitogen? How does it illicit an immune response?

Answer 7

polyclonal activators of T and/or B cells
ex: LPS – B cell mitogen (“PAMP”)
Concanavalin A (ConA) – T cell mitogen

this is a non-specific antigen

Question 8

What type of antigen generates immunological memory?

Answer 8

T-dependent (TD) antigens

through the help of cytokines
both T and B cells are activated

Question 9

Why are high and low doses usually not immunogenic?

Answer 9

they stimulate tolerance (the immune system does not respond)
high doses may cause the body to think it came from itself
low doses might not be worth the energy input required for an immune response

Question 10

What is an adjuvant?

Answer 10

adjuvants are compounds that when mixed with immunogens, makes them more immunogenic, producing a stronger immune response (helps the immune cells recognize the antigen)

an adjuvant cannot make a hapten immunogenic (have to have the carrier present)

NOT chemically bound to the immunogen (unlike the hapten-carrier)

Question 11

Why would we use adjuvants in vaccines?

Answer 11

in order to increase immune response against microbes

Question 12

What are the 3 mechanisms of action of adjuvants?

Answer 12

1. increase half-life of immunogens (e.g. slow release of immunogen)
2. increase production of inflammatory cytokines (e.g. stimulate TLRs on APCs)
3. improved presentation and co-stimulation of APCs to T cells