ABSTRACT
So far the immune system has been portrayed as ‘the good guy’, the great defender against intrinsic disease including malignancy, and extrinsic invaders such as infectious organisms. However, as with all biological systems, things can and do go wrong: diseases may arise because of genetic or acquired deficiencies in the immune system; the great defender may turn against self (autoimmune disease); the mechanisms that regulate the immune system may fail; or the immune system may work properly, but in the face of tricky or more aggressive customers the ‘normal’ response may in fact result in pathology. This chapter explores these issues.
