ABSTRACT
INTRODUCTION The immune system is one of the largest and most complex in the body. Its primary roles are the inactivation of potentially pathogenic micro-organisms and viruses, the prevention of infestation by parasites, and the suppression of tumours. Effective functioning of the immune system is dependent upon the availability of an effective and flexible arsenal with which to fight infection. The power of immune ‘effector’ mechanisms is well demonstrated by the damage associated with immunopathologies seen in diseases such as glomerulonephritis, rheumatoid arthritis and the extreme vigour of acute allograft rejection. The morbidity associated with genetic or induced immunodeficiency is also indicative of the importance of immune function. Clearly, sensitive, though reliable, mechanisms must exist to regulate the numerous functions of the normal immune system.
