Topic-immune Response

Defination:Immune response means any defensive reaction to foreign material by the immune system.

Types of immune response: there are two types of immune response:

1. Primary immune response

2. Secondary immune response

Immune response is acquired by two mechanisms:

*Antibody mediated immune response(humoral immunity)

*Cell mediated immune response (CMI)

1. Development of antibody mediated immune response (Humoral immunity):

In case of T-dependent antigens:

a.Most of the immunogens are T-dependent Ag. They cannot activate the B-cells directly. They take the help of helper T-cell to activate B-cell. Again the helper T-cells cannot recognize immunogen without class-II MHC Ag.

B.A small portion of these immunogen is taken up by macrophage- the APC (antigen presenting cell).The Ag will be processed & will be expressed on the surface of APC along with class-II MHC. The helper T-cell will now recognize the processed Ag along with class-II molecule on the surface of APC.

c. During presentation of Ag, APC secrete IL-I, which will activate helper T-cell to produce many lymphokines of which the IL4 & IL-5 will activate & proliferate the B cells. IL-4 causes proliferation of B-cell and IL-5 causes differentiation of B-cells to plasma cells. The plasma cells will then secret Ig, which subsequently bind with specific Ag, for elimination.

d.The memory cell is specific for these stimulatory Ag and has larger life span than normal B-cell.

This memory cell will participate in secondary immune response that is on subsequent exposure of the same Ag in the body. The secondary immune response will be more prompt & stronger.

In case of T-independent antigens:

T-independent Ag will bind with surface immunoglobulin receptors of B-cells & will remain as such.

Then they activate the B-cells and differentiate them to plasma cells to produce antibody.

Cytokines:

Cytokines are the biologically active molecules (low molecular weight proteins) released by specific cells and regulate the differentiation, proliferation or function of immune and inflammatory cells.