ANTIGEN

In immunology,  an antigen is an molecule capable of inducing an immune response ( to produce antibody) in the host organisms. Sometimes antigens are part of the host itself in a autoimmune disease.  Antigen are targeted by antibodies.

                                OR

A toxin or other foreign substance which induce an imnune response in the body, especially the production of antibodies is called antigen.

TYPES OF ANTIGEN

EXOGENOUS ANTIGEN

These antigen enter the body & circulating in the body fluid and caught by macrophages, dendritric cells etc.

Ex:-  Bacteria,  virus,  fungi etc

ENDOGENOUS ANTIGEN

These are the bodies own compound /fragments / cell are produced in body are processed by macrophage and later accepted by cytotoxic T-ells.

Ex:- Histocompatibility Leukocyte antigen (H. L. A).

AUTO ANTIGEN

These are normally proteins that are recognised by immune system of patient suffering from autoimmune disease.

Ex:- Nucleoproteins, Nucleic acids etc

ANTIGENCITY

It is the ability of a substance to combine specially with the antibody or cell surface receptor.

IMMUNOGENCITY

Immunogencity is the ability of an antigen to elicit a hunoral or cell mediated immune response.

HAPTEN OR INCOMPLETE ANTIGEN

The molecule that may bind to antibodies but can't elicit immune response. These molecule are called hapten.