Intestinal malabsorption, diarrhea, and wasting are frequent manifestations of HIV infection and may occur in early stages of disease in the absence of other enteric pathogens. However, mechanisms by which HIV affects intestinal mucosal morphology and function are not known. Our results suggest that SIV-infected rhesus macaques provide an excellent animal model to study AIDS-associated gastroenteropathy. Jejunal tissues from SIV- infected animals had depressed digestive enzyme activities and morphometric analysis showed crypt hyperplasia and increased mitoses suggesting a maturational defect in proliferating epithelial cells. The main objective of the present proposal is to elucidate the sequence of events leading to intestinal malabsorption in SIV-infected rhesus macaques in vivo, in a longitudinal study and to determine the effect of jejunal SIV infection on morphology and function. An effort will be made to determine whether these changes are a result of the direct SIV infection of the absorbing enterocytes or are mediated by cytokines secreted by SIV-infected inflammatory cells. SIV-infected animals will be followed for the development of malabsorption from initial viral exposure to the terminal stages of simian AIDS using D- xylose and fat absorption tests. Sequential jejunal biopsies, necropsy tissues and blood samples will be obtained from these animals. The dissemination of viral infection in intestinal mucosa will be determined and correlated with malabsorption, epithelial cell maturation and digestive enzyme activities. Statistical correlations will establish the relationship among mucosal infection, altered cell proliferation and morphology, and functional abnormalities. The level of cytokine expression will be determined in SIV-infected jejunal mucosa to determine whether cytokines are associated with pathogenesis. Jejunal explant cultures will be treated with recombinant cytokines and analyzed for epithelial cell proliferation and digestive enzyme synthesis. The in situ hybridization method will be used to localize nucleic acids of SIV and cytokines (IL-1, IL-2, IL-6, TNFalpha, TGFalpha, TGFbeta) in cells of jejunal mucosa. Levels and biological activities of cytokines (IL-1, IL-2, IL-6, TNFalpha) will be determined in jejunal mucosal homogenates. Findings will be correlated with jejunal pathology, dysfunction and degree of inflammation. Number of CD4+ helper and CD8+ suppressor T-lymphocytes and macrophages will be measured by immunohistochemical staining to determine populations of infiltrating mononuclear cells. Results obtained from the present proposal will define the role of intestinal mucosal SIV infection in the development of SIV-associated intestinal dysfunction. The research is aimed at elucidating the pathogenesis of altered intestinal morphology and function in SIV infection and determining the role of cytokines in this process. This information will be relevant in the design of therapy directed at the mucosal lesion early in the course of disease in an attempt to prevent malabsorption and wasting.