Human neutrophils present the antigen to antigen-specific memory CD4⁺T cells in an HLA-DR–dependent manner. Neutrophils from CMV- or influenza-seropositive donors were pulsed with pp65 or HA and cocultured with autologous CFSE-labeled CD4⁺ T cells for 5 days. (A) Representative plots of HA (where indicated) or pp65-specific proliferating CD4⁺ T cells for the indicated conditions. (B-C) Bars show percentages of pp65-specific proliferating CD4⁺ T cells. (C) HLA-DR neutralizing antibody strongly reduced CD4⁺ T-cell proliferation mediated by neutrophils whereas no reduction was observed in presence of the same concentration of isotype control (mean ± SEM, n = 3-8 donors); *P < .05, **P < .01 and #P < .01 vs CD4⁺ T cells only. (D) CD4⁺ T-cell proliferation induced by neutrophils alone or in presence of different amounts of BDCA-1⁺ MDCs (up to 10%) or CD14⁺ monocytes (up to 10%).