Question

Describe the features of antigens and how immune system recognises these antigens as being foreign

Answer 1

Features of antigens: An antigen must be a foreign substance to an organism to elicit an immune response. Antigens are mostly protein but some antigens are polysaccharide. It is believed that the presence of an aromatic radical is basic requirment for antigenicity. The molecular size of most active antigens are 14,000 to 6,00,000 Da. Antigenicity of an antigen increases with chemical complexity of the antigen. Particulate form of antigens are more active than soluble form of antigen. The most important feature of antigen is the presence of epitops through which antigen binds with antibody.

Recognition by immune system. Antigens contain epitops which is recognised by antibodies. Epitops are the specific segment of antigen. The shape of epitops determine that which antibody will bind to the antigens. Epitops are found on the surface of antigen.