MHC restriction of F peptide-specific CD4 T-cell responses. Inhibition of IFN-γ production by MHC class II-specific monoclonal antibodies B8.11.2 (anti-HLA-DR) and SPVL3 (anti-HLA-DQ). (A, C, and F) IFN-γ Elispot assay with PBMC from donors VB-5(A), VB-2 (C), and VB-7 (F). F peptide 18-mers (peptide numbers are given in the figure) were titrated, and B8.11.2 culture supernatant was used diluted 1:100 (white bars) and 1:4 (grey bars). The number of IFN-γ spots in unblocked cultures is shown (black bars). As a control for the specificity of MHC class II blocking, MHC class I-mediated stimulation by the influenza virus (Flu) matrix peptide M57-65 was also performed in the presence of B8.11.2. (B, D, and E) IFN-γ Elispots of donors VP-1 (B, left panel) and MP-4 (B, right panel), donor CE-7 (D), and donor JB-1 (E). Blocking performed with culture supernatant of B8.11.2 diluted 1:50 (white bars) and culture supernatant of SPVL3 diluted 1:100 (grey bar). Unblocked cultures are shown as black bars.