Tumor necrosis factor: its role in HIV/AIDS.

ABSTRACT

AIDS Tumor necrosis factor (TNF, cachectin), a cytokine secreted by macrophages and T-cells, mediates inflammatory and immune responses, and is associated with wasting in persons with malignancies or AIDS. In inflammation, TNF attracts and activates neutrophils, stimulating phagocytic function of neutrophils and macrophages. TNF also increases hepatic cell resistance to damaging parasitic effects; enhances endothelial permeability, causing edema; aids in wound healing by stimulating tissue and vascular growth; enhances lymphocytic activity through cytokine activation; acts with interleukin (IL) to produce fever, anorexia, lethargy and sleep; and possesses antitumor activity, particularly against the presumed origin of Kaposi's sarcoma, capillary endothelial cells. The host has an acute phase response (APR) following TNF- and IL-induced immunologic activation. TNF and IL decrease production and activity of lipoprotein lipase (LPL), resulting in reduced uptake and improper storage of fat; and they stimulate anabolism of fatty acids, causing hypertriglyceridemia. This "futile cycling" causes shuttling of fatty acids between adipose tissue and the liver, and use of muscle protein as the main fuel source. This, along with further muscular breakdown due to the increased caloric demands of fever, may affect cachexia. TNF benefits the HIV-infected through selective killing of HIV-infected cells, although effects may be dose and time dependent. The negative effects of TNF may be impeded by anti-cytokine therapy. Possible therapies include dietary N-3 fatty acid (fish oil), an inhibitor of TNF and IL production in vitro; pentoxifylline (Trental), another TNF production inhibitor; anti-TNF monoclonal antibodies; and soluble TNF receptors.^ieng