Dissemination of SIV after rectal infection preferentially involves paracolic germinal centers.

Homosexual transmission remains a major mode of contamination in developed countries. Early virological and immunological events in lymphoid tissues are known to be important for the outcome of HIV infections. Little data are available, however, on viral dissemination during primary rectal infection. We therefore studied this aspect of rectal infection in rhesus macaques inoculated with the biological isolate SIVmac251. We show that infection is established initially in lymph nodes draining the rectum. Infected cells and virions are localized mainly in germinal centers at that stage. With increasing viral burden, infected cells are found throughout the lymph node parenchyma. In addition the difference in viral load between lymph nodes draining the rectum and other lymph nodes is attenuated or abolished. We discuss this pattern of viral dissemination with respect to the physiology of the mucosal immune system. The pattern and kinetics of viral dissemination after rectal infection have important implications for the development of efficient mucosal vaccines.