The cellular and molecular pathways involved in the regulatory effects of pro-inflammatory and immunoregulatory cytokines on human immunodeficiency virus (HIV) expression were investigated. Synergistic induction of HIV expression was demonstrated in chronically infected U1 cells co-stimulated with several cytokines. Interleukin (IL)-4 and IL-10 potentiated HIV expression of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-alpha), IL-1, and IL-6. Autocrine stimulation of HIV replication by multiple endogenous cytokines was demonstrated in primary human peripheral blood mononuclear cells without necessity of mitogen stimulation as well as in monocyte-derived macrophages. In this system, as well as in U1 cells, cytokine antagonists such as IL-1ra and pentoxifylline suppressed HIV replication. In vivo, macaques infected with SIV showed a peak of cytokine production coincidental with the early peak of viremia that characterizes both SIV and HIV primary infections. At the molecular level, a central role of NF-kappaB in HIV expression has been further demonstrated. Isogenic cell clones of the CD4(+) U937 cell line showed either high (PLUS clones) or very low (MINUS clones) ability to support HIV replication, a functional dichotomy that was correlated with the inability of MINUS clones to support the transactivation of the viral promoter. The functional defect was found dependent upon a different pattern of NF-kappaB-related proteins, and specifically, with the presence of a different isoform of the p65 subunit of NF-kappaB. Finally, mutagenesis conducted on the p50 subunit of NF-kappaB resulted in a protein which maintained the ability to specifically bind to the DNA target sequences, but did not dimerize with the p65 subunit, therefore acting as a trans-dominant mutant of NF-kappaB-mediated transcription.
