Role of the cytoskeleton in cell-to-cell transmission of human immunodeficiency virus.

We previously observed that when human immunodeficiency virus (HIV)-infected T lymphocytes are added to epithelial cells, they adhere, polarize, and secrete virions unidirectionally onto the epithelium. Epithelial cells subsequently take up virus and become productively infected. We report here that colchicine treatment of T-lymphocyte suspensions induced lymphocyte polarization, redistribution of F-actin into a pseudopod, and secretion of HIV from the pseudopod. Immobilization of T lymphocytes on negatively charged plastic also caused redistribution of F-actin and unidirectional secretion of HIV onto the plastic. As neither colchicine nor adhesion caused an increase in HIV secretion, they apparently act by focusing secretion to the tip of the pseudopod. We speculate that adhesion-induced polar secretion of HIV, from activated mononuclear cells onto epithelia, is a cytoskeleton-mediated process which may be involved in HIV transmission in vivo.