Soluble factor(s) mediates resistance of CD4^dimCD8^bright T cells to M-tropic HIV infection. (A) Supernatant from SEB-stimulated CD8⁺ T cells or unstimulated CD8⁺ T cells was added to primary isolate (302073, 302140, 302056, 302072, 302144) or IIIB-infected PBMC cultures. HIV replication was determined by extracellular production of HIV p24, evaluated by ELISA on day 7 after infection. Values represent mean p24 (picogram per milliliter) production from 4 donors. A comparison of each virus treatment between unstimulated supernatant and SEB-stimulated supernatant demonstrated that all individual p24 values decreased with SEB-stimulated supernatant (Wilcoxon signed rank = 0.068). Although not significant at the .5 level, this is the smallest P value attainable for this sample size. Because the expected behavior of supernatant inhibition by primary virus strains was similar (decreased), all the data were combined and a 2-way repeated measures analysis of variance (ANOVA) on the log counts showed there was a main effect of SEB-stimulated supernatant addition (F_1,3 = 25.929, P = .015). (B) Supernatant from SEB-stimulated CD8⁺ T cells or unstimulated CD8⁺ T cells was treated with neutralizing antibodies to β-chemokines then added to primary isolate (302073)–infected PBMC cultures. HIV p24 expression was evaluated by ELISA 7 days after infection and treatments. □ indicates no antibody; ▦, control antibody; and ▪, anti–β-chemokine antibody.