Question

Name the region of the antibody that determines their effector function and list the 5 main types. List and explain the three main effector functions mediated by this region of the antibody.

Answer 1

Antibodies are immunoglobulin molecule which are humoral immune system and produced by B lymphocytes. Antibodies are Y shaped having two Fab (antigen binding sites) and one Fc ( fragment of crystallization). Fab binds to antigen epitope and Fc region mediate effector function of antibody by interacting with immune cell ( phagocytes, macrophages neutrophils) having Fc receptor. It also produce effector function by activating complement pathway.

So it is Fc fragment which mediate the effector function of antibody.

Antibodies are divided into five main types based on difference in constant region of heavy chain( C_{​​​​​​H} ). These are immunoglobulin G ( gamma), immunoglobulin A(Alpha), immunoglobulin M ( mu), immunoglobulin D ( delta) and immunoglobulin E ( epsilon).

Effector functions

Antibodies can mediate different effector functions like complement mediated cell lysis by activating membrane attack complex, phagocytosis, neutralization, Agglutination and precipitation.

1) Complement system activation : when antibody antibody complex activates classical complement pathway some molecules are produced in that activation process that attract phagocytes to site of infection leading to phagocytosis. Main effect of Complement activation is that it induce cell lysis by activating membrane attack complex(MAC) so it can lyse microorganisms.

2) Antibody dependent cell cytotoxicity (ADCC) : In this process antibody bind to the antigen present on surface of pathogen/ target cell. After antibody binding Fc region of antibody is recognised by different immune cell(having Fc recpetor) for killing pathogen by NK cell.

3)opsonisation agglutination

Antibody also act as opsin molecule by coating the antigen of pathogen which then can be pagocytosed by macrophages or killed by degranulation of mast cell when Fc fragment of antibody is recognised.Macrophages kill cell by secreting lytic enzymes. Different type of cell performs different action like opsonisation by macrophages, degranulation by mast cell etc.