Severe malnutrition impairs immune function and decreases resistance to infection [24]. Lymphoid tissues are vulnerable to the damaging effects of malnutrition, and lymphoid atrophy is a prominent feature of nutritional deprivation. All types of immune cells and their products (i.e., interleukins, interferons, and complements) depend on metabolic pathways that use various nutrients as critical cofactors for their actions and activities. Thus, host defense mechanisms are altered in protein-calorie malnutrition and during deficiencies of trace elements and vitamins.