Protein-Energy Malnutrition and Infectious Disease

Abstract

The immune system plays a leading role in fighting off the constant bombardment of our bodies by invading pathogenic organisms, such as bacteria, fungi, viruses, toxins, and allergic compounds. Also, the immune system is intimately linked to the quality and quantity of nutrient intake (1,2). The host is defense-regulated and maintained by two branches of the immune system. One is cell-mediated immunity, carried out primarily by the CD4+ Th-1 and CD8+ T lymphocytes, which plays a pivotal role in cytotoxic responses against malignant cells and cells infected with intracellular bacteria and viruses. The other branch is humoral (antibody-mediated) immunity, of which the B lymphocyte plays a dominant role, to ward off and/or destroy extracellular pathogens. The T lymphocytes may also influence humoral immunity, as the Th-2 CD4+ T lymphocyte subset secretes a wide variety of antibody-inducing cytokines. The Th-1 CD4+ T lymphocyte produces primarily interleukin-2 (IL-2) and interferon gamma (IFN-y) and the Th-2 population produces primarily IL-4, -5, -6, and -10. Antibody isotype production (IgA, IgE, IgG, etc.) is dependent on the kind of cytokine produced to fight invading antigen assaults. Unfortunately, this vast array of defense mechanisms is not impregnable. Primary causes of a breakdown in these lines of defense (i.e., serious breakdown of our immune system) is either chronic or acute under nutrition and malnutrition.