astrocyteconditioned medium stimulates hiv1 expression in a chronically infected promonocyte clone human promonocytic cells chronically infected with human immunodeficiency virus1 hiv1 clone u115 were grown in the presence of media conditioned by primary rat cortical astrocytes and hiv1 expression was assessed by measuring reverse transcriptase activity media conditioned by nonstimulated and lipopolysaccharide lpsstimulated astrocytes induced the expression of hiv1 21fold and 41fold respectively lps alone media conditioned by the uninfected parental cell line of u115 u937 and culture media from four other cell lines had no effect on viral expression the magnitude of induction was time and dosedependent tumor necrosis factor alpha tnfalpha was detected in lpsstimulated astrocyteconditioned medium and the hivinducing capability of the medium was neutralized in part by an antibody to recombinant murine tnfalpha these results suggest a role for astrocytes in the induction of hiv expression and thus in the pathogenesis of hiv1 infection in brain