Inhibition of IFN-γ release by anti–HLA class II mAb. HB-1–specific CD4⁺ clones M3A4 and R3A8 were stimulated with autologous EBV-LCLs pulsed with the HB-1_19-41 peptide or the HB-1_4-25 peptide, respectively. Blocking studies were performed by using purified anti–HLA-DR (L234), anti–HLA-DP (B7/21), or anti–HLA-DQ (Tü22) mAb (10 μg/mL) which were present throughout the assay. Error bars represent 1 SD of triplicates.