ABSTRACT
The immune response is an essential defence mechanism. However, it may be defective, disorganized or overactive. The body has the potential to stimulate its own immune system so that antibodies are produced against itself. Normally this situation is prevented, for example, by tolerance, but if this fails then autoimmune disease results. Deficiencies in the immune system may be congenital or result from disease (notably AIDS from HIV-1 infection) or the use of immunosuppressant drugs, particularly cytotoxic agents (e.g. cyclophosphamide, 6-mercaptopurine), glucocorticosteroids and immunophilins (e.g. ciclosporin and its analogues). By the same token, these are the very drugs that are used clinically as immunosuppressants when it is necessary to damp down an inappropriate immune response.
