ANTIGENS & IMMUNOGENICITY

Question 1

*Immunogen is

Answer 1

*Immunogen: a stimulus that produces a humoral or cell-mediated immune
response

Question 2

*Antigen:

Answer 2

any substance that binds specifically to an antibody or a T-cell
receptor

Question 3

*Epitope:

Answer 3

the portion of an antigen that is recognized and bound by an Ab or
TCR/MHC complex

Question 4

*Hapten:

Answer 4

a low molecular weight molecule that can be made immunogenic by
conjugation to a suitable carrier

Question 5

The two attributes of antigenicity are:

Answer 5

Induction of an immune response (immunogenicity).
Specific reaction with antibody or sensitized cells (immunological reactivity).

Question 6

Examples of haptens are

Answer 6

antibiotics, analgesics Penicillin, and other low molecular weight compounds.

Question 7

What are cytokines?

Answer 7

Low molecular weight hormone-like proteins or
glycoproteins

Question 8

Actions of cytokines

Answer 8

Pleiotropy
Redundancy
Synergy
Antagonism

Question 9

pleiotropy

Answer 9

multiple biological actions

Question 10

redundancy

Answer 10

the phenomenon in which, and the ability of, multiple
cytokines to exert similar actions

Question 11

synergy

Answer 11

two or more cytokines acting together

Question 12

antagonism

Answer 12

cytokines causing opposing activities

Question 13

The Humoral Immune Response

Answer 13

The Humoral Immune Response (HIR) is the aspect of immunity that is mediated by secreted antibodies produced in the cells of the B lymphocyte lineage called plasma cells

Question 14

igG

Answer 14

Dominant Ig in immune response.
* Major antimicrobial activity in plasma and extravascular fluids (in milk
also).
* IgG1, IgG3 & IgG4 cross placenta.
* IgG3 most effective complement activator > IgG1&raquo_space; IgG2; IgG4 does
not activate complement.
* IgG1 & IgG3 bind with high affinity to Fc receptors (FcγR) on phagocytic
cells mediating opsonization

Question 15

igA

Answer 15

Monomer in serum and Dimer in secretions.
†It is secreted in quantities more than any other Abs.
†IgA-secreting plasma cells are concentrated along
mucus membrane surfaces (MALT).
†Doesn’t activate classical complement pathway.
It does not crosses the placenta.
†Secretory IgA is important in defense against
bacteria and viruses

Question 16

igM

Answer 16

† Monomeric IgM is expressed as
membrane-bound antibody on B
cells (B-cell receptor).
† IgM is secreted by plasma cells as
a pentamer in which 5 monomer
molecules joined by disulphide bonds
and a J (joining) chain
†First to appear in neonate and in the normal immune response.
†
†It does not cross placenta and does not diffuse well in tissue fluids.
†It does not have hinge region.

Question 17

igE

Answer 17

†Slightly larger, more rigid than IgG.
†No hinge.
†Classical antibody of anaphylaxis (Type I
allergies) and certain parasitic infections

Question 18

igD

Answer 18

Largely confined to membrane of mature B-cell
together with membrane IgM.
†Not expressed on immature B-cells