Immune deficiency diseases.

Paediatricians have long been deeply concerned with problems of infection. The sharp decrease in childhood mortality in recent decades in highly developed countries is mainly due to progress in preventing and treating infection: for example, in Switzerland in 1973 there were about 88 000 births and only 16 deaths due to infection in children aged between 2 and 4 years in contrast to 76 killed by accidents. In underdeveloped countries more than 50% of the children die during childhood, infection being a predominant cause. Individual differences in the ability to cope with pathogens have been assumed for a long time, but were not studied scientifically until the introduction of antibiotics had resulted in control of the major infections. At this time paediatricians began to pay more attention to constitutional and inherited diseases, and made observations on congenital deficiencies of selective defence mechanisms which have contributed to a better understanding of the normal immunological functions. The basis of the currently used classification of primary immune deficiency diseases is the 'twocomponent concept' (Cooper, Paterson, and Good, 1965; Good and Fisher, 1971). Its main postulate, the distinction between T and B lymphocytes, is wellknown, and provides a useful workinghypothesis clinically.