We report in this study that repeated tumor necrosis factor alpha (TNF-␣) pretreatment, starting before and continued after infection by human immunodeficiency virus type 1 (HIV-1), inhibits replication of the monocytotropic Ada strain in primary tissue culture-differentiated macrophages (TCDM), as assessed by sixfold lower levels of reverse transcriptase (RT) activity than that in untreated cells and absence of syncytium formation in TCDM cultures. In order to determine the pathways involved

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... inhibition of HIV-1 replication in primary TCDM pretreated with TNF-␣, we tested TNF-␣ mutants T55 and T75, which recognize either the 55-kDa (TNF-R1) or the 75-kDa (TNF-R2) TNF receptor, respectively. Pretreatment of TCDM with the T75 mutant decreased the RT activity compared with that in untreated infected control cells fivefold and almost totally inhibited syncytium formation. In contrast, when TCDM were pretreated with the T55 mutant alone, syncytia were observed and RT activity was decreased about one-half. These results suggest that the inhibition of HIV-1 replication in TCDM pretreated with TNF-␣ might be mediated mainly through the 75-kDa TNF receptor (TNF-R2) rather than through the 55-kDa receptor (TNF-R1). Inhibition of HIV-1 replication in TCDM was observed with both T75 mutant pretreatment and posttreatment, starting at 1 h or 3 days after infection, whereas posttreatment with the T55 mutant, but not pretreatment, stimulated HIV-1 growth in primary TCDM. Both pre-and posttreatment with TNF-␣ inhibited HIV-1 replication in primary TCDM. The stimulation of HIV-1 replication by TNF-␣ in a chronically infected promonocytic cell line, U1, which contains two copies of integrated provirus, was mediated through the 55-kDa TNF-R1 alone and not through the 75-kDa TNF-R2. These results demonstrate that the 55-kDa TNF-R1 is involved in postintegration stimulation of HIV-1 while the 75-kDa TNF-R2 is involved in the inhibition of an early step of the viral life cycle in primary human TCDM.