We have been performing the following studies: 1. cytokine production by monocyte/macrophage persistently infected with HIV; 2. quantitative infectious cell center (ICC) assays for detection of peripheral blood mononuclear cells (PBMC) infected with HIV; and 3. characterization of monocyte/macrophage-tropic viruses. The results show that although HIV infection itself induced significant levels of mRNAs for IL-1Beta, TNF-Alpha, IL-6, and IL-8, the levels of lipopolysaccharide (LPS)-induced mRNAs for IL-1Alpha, IL-1Beta, TNF-Alpha, IL-6, and IL-8 in HIV-infected human cultured macrophages were much lower than those in uninfected LPS-stimulated human macrophages. Consistent with the IL-8 mRNA expression data, the HIV-infected macrophages produced a much lower amount of IL-8 protein, as measured by a radioimmunoassay, than uninfected LPS-stimulated cells over an 18-day culture period. These results suggest that HIV-infection generally suppresses the inducible cytokine production in human macrophages. In our studies using ICC assay, PBMC that are infected with a rapid/high cytopathic virus (HIV-1RF) form discrete syncytia by co-culturing with a CD4-positive cell line in microtiter plates. Similar results were observed with monocytes/macrophages. Further studies will be performed with slow/low, as well as other rapid-high isolates in this system. We have also determined the growth kinetics of a monocyte-tropic virus infecting monocytes/macrophages by the detection of viral protein components. Preliminary results showed that gp120 was dissociated from virus particles.