Lec 5 antigens

Question 1

What are antigens?

Answer 1

any substances recognized by the immune system and react with T or B lymphocytes. Can be self or non-self.

Question 2

Immunogen

Answer 2

any foreign substance which can stimulate the immune system to produce a specific immune response(humoral or cellular)

Question 3

Hapten

Answer 3

substances of low molecular weight, cannot induce an immune response unless coupled to a protein carrier.

Question 4

Examples of haptens

Answer 4

drugs such as penicillin, aspirin or cosmetics and soap

Question 5

Criteria needed for immunogenicity

Answer 5

1-Foreighness.
2-Molecular weight : more than 10 kDa(kilo-Dalton).
3-Chemical complexity.(proteins,CHO3,lipids,nucleic acids)
4-Epitopes: variable multiple epitopes.
5-Degradability: susceptible to enzymatic degradation in APCs
6-Dose: high or low: number of doses(booster doses)
7-Route of administration: parenteral or oral
8-Adjuvants:substances when mixed with an antigen before administration will increase the immune response to that antigen.

Question 6

Types of antigens

Answer 6

1-Bacterial antigens
2-Viral antigens
3-Human tissue antigens
4- Blood group antigens
5-Histocompatability antigens

Question 7

Bacterial antigens can be

Answer 7

soluble antigens(products of a microbe): exotoxins,enzymes,hemolysins
cellular antigens: capsular,flagellar,somatic antigens

Question 8

Examples of soluble antigens

Answer 8

products of a microbe: exotoxins,enzymes,hemolysins

Question 9

Examples of cellular antigens

Answer 9

capsular,flagellar,somatic antigens.

Question 10

Viral antigens may be

Answer 10

• protein coat viral antigens

- soluble antigens

Question 11

Examples of soluble antigens

Answer 11

soluble nucleoproteins in Inlfluenza viruses.

Question 12

Blood group antigens examples

Answer 12

A,B and Rhesus antigens.

Question 13

Histocompatability antigens examples

Answer 13

• MHC I on surface of all nucleated cells

- MHC II on APCs(B-cells,macrophages,dendritic cells and activated T-cells)

Question 14

Antigens can be either ___ or ____

Answer 14

infectious / microbial , or noninfectious

Question 15

Examples of infectious/microbial antigens

Answer 15

• bacterial
• viral
• protozoal
• helminths

Question 16

Examples of noninfectious antigens

Answer 16

• self antigens
• food antigens
• plant products
• dust
• cell surface proteins
• synthetic chemicals
• venoms
• insect toxins

Question 17

What are antigen epitopes?

Answer 17

the smallest part of the antigen that binds to the antigen receptor (TCR or BCR).

Question 18

What may each epitope be composed of?

Answer 18

4-7 amino-acids or monosaccharide residues

Question 19

Chemical families of antigens

Answer 19

1- Proteins
2- Polysaccharides
3- Nucleic acids
4- Lipids

Question 20

Describe protein antigens

Answer 20

(most potent immunogens) and all proteins are immunogenic.

Question 21

Describe polysaccharide antigens

Answer 21

blood group antigens(A and B antigens on RBCs) glycoproteins: potentially but not always immunogenic.

Question 22

Describe nucleic acid antigens

Answer 22

poor immunogens ,but immunogenic when coupled to a protein carrier.

Question 23

Describe lipid antigens

Answer 23

rarely immunogenic but lipoproteins are immunogenic.

Question 24

What do T-cell receptors recognize?

Answer 24

Recognize fragments of protein (peptides) associated with MHC molecules on surface of APCs (MHC restricted)

Question 25

What do T helper cells recognize?

Answer 25

-recognizes peptide associated with MHC II molecules

Question 26

What do cytotoxic T cells recognize?

Answer 26

-recognize peptides associated with MHC I

Question 27

Relationship between T cells and MHC

Answer 27

T-cells are MHC restricted

Question 28

What do B-cells receptors =?

Answer 28

IgM and IgD

Question 29

What do IgM and IgD recognize?

Answer 29

``` Proteins. Polysaccharides. Nucleic acids. Some lipids (glycolipids and lipoproteins) Haptens ```

Question 30

Relationship between B cells and MHC

Answer 30

Do not need MHC to recognize an antigen(not MHC restricted),can recognize soluble antigens

Question 31

Relationship between B cell receptors and APCs

Answer 31

Do not need the antigen to be processed or degraded by APCs

Question 32

What are superantigens?

Answer 32

Class of antigens that result in excessive activation of the immune system. Not processed by APCs.

Question 33

Where do superantigens bind?

Answer 33

Can bind to both the variable region of ß chain on TCR of T-cells and to MHC II on APCs.

Question 34

What do superantiens act as between the variable region of ß chain on TCR of T-cells and to MHC II on APCs?

Answer 34

They act as a clamp between the two, providing a signal for T cell activation.

Question 35

What do superantigens activate?

Answer 35

Activates large number of T-cells resulting in massive cytokines release and massive pathological effect.

Question 36

How do superantigens differ from classic antigens?

Answer 36

1-Superantigens are not processed. They interact with the MHC molecules outside the peptide-binding groove. 2-They are active at very low concentrations 3-Stimulate many T-cells causing the release of large amounts of cytokines. This causes systemic toxicity

Question 37

Examples of superantigens

Answer 37

- Staphylococcal enterotoxins - Staphylococcal Toxic Shock Toxin - Staphylococcal Exfoliating toxin - Streptococcal pyrogen exotoxin