EARLY REGENERATION OF THYMIC PROGENITORS IN RHESUS MACAQUES INFECTED WITH SIMIAN IMMUNODEFICIENCY VIRUS

The thymus plays a critical role in the maturation and production of T lymphocytes and is a target of infection by human immunodeficiency vi rus (HIV) and the related simian immunodeficiency virus (SIV). Using t he SIV/macaque model of AIDS, we examined the early effects of SIV on the thymus. We found that thymic infection by SIV resulted in increase d apoptosis 7-14 d after infection, followed by depletion of thymocyte progenitors by day 21. A marked rebound in thymocyte progenitors occu rred by day 50 and was accompanied by increased levels of cell prolife ration in the thymus. Our results demonstrate a marked increase in thy mic progenitor activity very early in the course oi. SIV infection, lo ng before marked declines in peripheral CD4(+) T cell counts.