Immune function in the malnourished host.

Deficiencies of protein, energy, and specific vitamins and minerals impair function of various components of the immunological network and therefore weaken host defense. These various deficiencies may affect specific loci within the network, but because of the interrelations between the different systems, the ultimate effect may be quite broad. Patients with PEM often suffer infections, which may also impair the immune function. It is difficult to separate effects of malnutrition from those of infection, a fact recognized in the recent coinage of the term malnutrition-infection complex. On the basis of the available information it appears that PEM and associated deficiencies of nutrients cause a major impairment in the T lymphocytes and the complement system. They have relatively less effect on the B lymphocytes and the phagocytes directly; however, normal B cell activity is dependent on regulatory influences of T cells and the phagocytic cells require mediators generated from the activation of complement. Therefore these cells also are functionally defective in PEM. The consequence of these deficiencies of function of the immune system in the malnourished host is heightened susceptibility to and a less vigorous response to infections. These defects can be generally reversed by nutritional rehabilitation.