Abstract
The following is a review of an emerging topic in the literature which has led to new hypotheses regarding the mechanisms of pathogenesis of the various tissue specific AIDS associated syndromes. The fundamental hypothesis in this review proposes that HIV-1 is able to increase lymphocyte and monocyte localization in tissues where released HIV-1 proteins cause local tissue damage leading to any one of the various AIDS associated syndromes. It is also hypothesized here that syndromes associated with other lymphotrophic viruses result from the ability of these viruses to direct leukocyte extravasation of blood vessel walls and to initiate tissue specific pathogenesis. Further, it is suggested here that new concepts and strategies for delivering gene therapy to specific tissues can be derived from our understanding of the mechanisms through which lymphotrophic viruses localize in specific tissues. HIV-1 infection of lymphocytes and monocytes leads to increased adhesion of these cells to vascular endothelium and extracellular matrix molecules. In addition, HIV-1 infection of various leukocytes leads to increased secretion of extracellular matrix degrading matrix metalloproteinases. Increases in leukocyte adhesion and matrix metalloproteinase secretion are associated with the normal mechanisms through which leukocytes localize in tissues during inflammation. The ability of HIV-1 to activate leukocyte adhesion and matrix metalloproteinase secretion suggests that HIV-1 has evolved a way to take advantage of leukocyte inflammatory mechanisms in order to exit the blood stream and gain access to body tissues. The ability of HIV-1 to use infected cells to localize in various tissues may lead to the establishment of HIV-1 reservoirs in tissues. Such viral reservoirs may cause the various tissue specific AIDS associated syndromes. AIDS patients have been found to have elevated adhesion molecules (integrins, and cell adhesion molecules or CAMs) on their peripheral blood lymphocytes (PBLs). While there is little clinical evidence that the tissue localization of HIV-1 infected leukocytes are the cause of the HIV-1 related syndromes, studies in vitro and with animal models have shown that the HIV-1 gene products Tat, Rev and gp120 are potent neurotoxins. It has also been shown that Tat can contribute to the growth of cells from Kaposi's sarcoma lesions. Further, HIV-1 infected cells have been shown to secrete cytotoxic levels of a variety of growth factors and small molecules. Thus, it is likely that the localization of HIV-1 infected cells in specific tissues could contribute to the HIV-1 associated syndromes such as AIDS dementia, HIV-1 related interstitial lung disease, HIV-1 associated nephropathy, the HIV-1 wasting syndrome and perhaps AIDS associated Kaposi's sarcoma and hyperproliferative skin disorders. This review will examine studies in the literature which demonstrate that HIV-1 infection increases leukocyte adhesion and matrix metalloproteinase secretion. Clinical reports of AIDS patient's leukocyte integrin levels will also be reviewed and evidence that tissue localized HIV-1 infected cells could contribute to a variety of HIV-1 associated syndromes will be presented.