Contribution of CTLA-4 to HLIL-mediated suppression of PBMC responses. The effects of blocking CTLA-4 binding by the addition of anti–CTLA-4 F(ab)₂ antibody to 1:1 mixtures of HLIL and paired PBMC cultures stimulated with mitogen (ConA), recall antigen (PPD), or primary antigen (KLH). The vertical axis indicates IFN-γ secretion and proliferative responses expressed as a percentage of responses obtained from PBMCs cultured alone (up to 100% maximum). The results for samples from individual patients are linked by solid lines. Each patient (n = 10) is identified by a symbol as in Figure 2.