Effect of ionizing radiation on immunity.

Ionizing radiation has a deleterious effect on the immunity mechanism, particularly when large but sublethal doses are applied over a short period of time. The hematopoietic system is extremely sensitive, and a fall in the lymphocytes is one of the most characteristic manifestations. The normal balance of the microflora of the intestinal and respiratory tracts is disturbed, which results in a bacteremia and may lead to death of the host. Active immunity is seriously interfered with if the irradiation occurs shortly before the injection of an antigen. There is also reduced resistance to pathogenic micro-organisms, which may lead to fatal infections. Prolonged irradiation at low levels does not seem to affect immunity adversely. Active immunization should be carried out well in advance of exposure to radiation, and supportive treatment commenced immediately after exposure to large doses.