Specific immune responses are directed against antigens. Antigens are molecules or parts of molecules that are usually large, complex, and foreign. A given molecule can have a number of antigenic determinant sites that stimulate the production of different antibodies.
Specific immunity is a function of lymphocytes.
These subclasses differ in regard to the polypeptides in the constant region of the heavy chains. The combination of antibodies with antigens promotes phagocytosis. Antigen-antibody complexes activate a system of proteins called the complement system. This results in complement fixation, in which complement proteins attach to a cell membrane and promote the destruction of the cell. Specific and nonspecific immune mechanisms cooperate in the development of a local inflammation.