Define Proteins in the immune system?

Proteins such as γ-globulin serve to protect the body against foreign cells. The immunoglobulin produced by lymphocytes is the large polypeptides having more than one basic monomeric unit. These proteins differ in their amino acid structure, which in turn, affect their secondary, tertiary and quaternary structures. Just as the amino acid sequence of an enzyme determines substrate specificity, the amino acid sequence of the immunoprotein assures antigen-antibody specifically. The initiation of synthesis of particular immunoglobulins by the lyinphocytes requires the binding of LW antigen (a foreign protein) to the cell surface at particular locations called 'antigen receptors'. The immunoglobulin synthesized binds with the foreign protein immobilizing it.