The Pattern of Infection in Immunodeficiency

Abstract

Although experiments in animals can tell us something about the mechanisms of protection against infection, the relevance to human disease is usually uncertain. The study of rare immunodeficiency disorders has enabled us to make some clear statements on the critical role of individual host defence mechanisms against infection. It is likely that new genetically determined defects in relatively minor aspects of host defence or inflammation (e.g. lymphokines) will soon be discovered and enlighten us on the efficiency of the many ‘back-up’ mechanisms for dealing with infecting organisms. The problem with many of the known severe immunodeficiency disorders, such as severe combined immunodeficiency, is that more than one cell type is involved, making it difficult to link the clinical pattern of infection with any specific defect. Furthermore, it can be difficult to locate the immune defect in patients who are chronically infected with an organism, since the infection itself may cause secondary ‘abnormalities’ in the immune system, as is seen in mucocutaneous candidiasis. Nevertheless, studies in patients with immunodeficiencies involving antibody production and neutrophil function have enabled us to link defence mechanisms to specific infections. Most of these studies have been undertaken on patients in advanced countries, and the results may not apply to individuals in the Third World who are more frequently exposed to a wider range of organisms. In this situation a relatively minor defect in an amplifying or back-up mechanism may be potentially lethal.