Human immunodeficiency virus (HIV) infection often has effects on the
hematopoietic system which can be distinguished from the concurrent ef
fects of medications or opportunistic infections. Exactly how the viru
s mediates these effects remains uncertain, but both in vivo and in vi
tro studies have pointed up possible direct and indirect modes of hema
topoietic suppression. Whether a significant fraction of CD34+ cells i
n vivo are infected with HIV remains controversial, but most studies u
sing in situ polymerase chain reaction techniques would suggest not. O
ther more indirect modes of hematopoietic cell suppression such as pro
duction of autoantibodies, production of other humoral inhibitory fact
ors, T-cell mediated suppression of hematopoiesis, or production of in
hibitory or stimulatory cytokines may also be contributory. It is prob
able that several of these mechanisms may occur simultaneously, and an
increased understanding of their role may lead to improved strategies
to correct the cytopenias which often accompany HIV disease.