In contrast to adjuvants, there are immunosuppressants, which include several physical agents (such as X-rays or gamma rays), chemical reagents and biological agents that suppress the immune response in animals.

Some corticosteroids, purine analogs, folic acid antagonists and alkylating agents are potent immunosuppressants. The enzymes ribonuclease and asparaginase also suppress immune, responses.

The suppression of antibody production can be brought about by anyone of the following five general biological means:

(i) There may be a deficiency in the ability of cells to synthesize gamma globulins (components of immunoglobulins). This deficiency is called hypogammoglobulinemia or agammoglobulinemia.

(ii) There may be a competition between different antigens. Thus, one antigen may suppress the immune response to another antigen.

(iii) Administration of an antilymphocyte serum (ALS) causes loss of lymphoid cells and reduction in the antibody response to antigens. Antilymphocyte serum is prepared by immunization of a heterologous species with cells from lymph node, thymus or spleen.

(iv)There is a feedback inhibition of immunoglobulin production. Passively administered antibody often inhibits the production of new antibodies.

(v) Some systems might develop immunologic tolerance. The system may have tolerance to a specific antigen and would not product its antibodies.