Malnutrition is bad for the immune system

Abstract

Malnutrition and infections interact synergistically. Together. they result in high morbidity and mortality especially in the very young in the developing world. There are two important links between primary malnutrition and infections; first, the macroenvironment of poverty, second, the body’s complex system of defence against infection. The malnourished child is more susceptible to infection. The infective load is continuously high. Nutritionally speaking, the child cannot afford good barriers to infection. The epidermis and buccal epithelium atrophy as do the gastrointestinal and respiratory tract linings. There is reduction in quantity and quality of their secretions so there is reduced flow of anti-infective agents along their surfaces. In particular, the output of gastric acid, secretory IgA and lysozyme is reduced. Microorganisms can not only easily colonize the various surfaces, they also invade the tissues following the slightest trauma to such weak barriers. The microorganisms having invaded, the malnourished child’s resistance to infection is poor. Many non-specific defences are reduced. Leucocyte concentrations of lysozyme. lactoferrin. myeloperoxidase and interferon concentrations are low: plasma lysozyme and transfertin are low: polymorph leucocyte production, mobilization, chemotaxis and capacity to kill bacteria are reduced; complement components and NK cell activity and responsiveness are reduced. The acute phase response is blunted. Infections are therefore difficult to diagnose. There are few clinical. haematological or radiological signs of inflammation, either local or systemic. Infection does not cause the normal fall in plasma zinc or iron and there is no rise in plasma copper. These are most apparent in children with oedematous malnutrition. The production of cytokines. ILI. IL-6 and TNF-n. by monocytes and the hepatic synthesis of acute phase proteins. C-reactive protein and serum amyloid A, are reduced.