Immunohistochemical detection of simian immunodeficiency virus (SIV) in rectal mucosa of experimentally infected rhesus macaques (Macaca mulatta)

Experimental simian immunodeficiency virus (SIV) infection is the most appr opriate animal model for human HIV infection. Eight male rhesus monkeys (Ma caca mulatta) were intravenously or intrarectally infected with SIVmac251/M PBMC to comparatively investigate the distribution and spread of the virus within the rectum during the course of the disease. SIV-positive cells were immunohistochemically detected in rectal biopsies obtained at days 3 and 7 and week 2, 4 and 12 postinfection. SIV-expressing cells were detected for the first time at one week after experimental infection and were present i n the lamina propria and lymph follicles. Numbers of positive cells per ind ividual animal varied strongly in time, with a more rapid rise in animals w ith rapid progression of the disease. Differences were not observed between intravenous and intrarectal infection. Our observations support the signif icance of the intestinal tract as target organ in initial pathogenesis of S IV infection.