GT inhibits T-cell activation via effects on antigen-presenting cells. CFC was performed to assess functional activation in CD4⁺ and CD8⁺ T cells after stimulation with SEB or CMV antigens. Cells were either cultured in the absence of GT (□) or with 35 ng/mL GT (▪). Panel A shows the effects of GT on SEB-stimulated CD4⁺ cells; panel B in CD8⁺ cells. Panel C shows the effects of GT on CMV-stimulated CD4⁺ cells; panel D in CD8⁺ cells. When GT was added at time 0 and washed at 1 hour, we observed a significant abrogation of functional T-cell responses (no GT control percentage always reported first): 14.6% vs 0.64% for CD4⁺ T-cell responses to SEB (P = .0002), 6.34% vs 0.53% for CD8⁺ T-cell responses to SEB (P = .0006), 1.96% vs 0.27% for CD4⁺ T-cell responses to CMV lysate (P = .03), and 0.78% vs 0.26% for CD8⁺ T-cell responses to an overlapping CMV pp65 peptide mixture (P = .028). When GT was added after the first hour of incubation and present through the remainder of the 6 hours of incubation, the magnitude of functional responses was comparable to that of the cells incubated without GT: 14.0% vs 10.5% (SEB-CD4), 5.84% vs 4.16% (SEB-CD8), 1.86% vs 0.91% (CMV lysate-CD4), and 1.37% vs 1.03% (pp65 mix-CD8). None of these represented a significant difference (P values were all ≥ .09). Error bars indicate SEM.