Proliferative response of preG- and G-CD4 cells to allogeneic, DR-mismatched PBMC in unidirectional MLC and to immobilized CD3-specific IgM in the presence of IL-2. (A) Different numbers (2.5, 1.25, and 0.625 × 10⁴) of preG-CD4 responders (solid lines) or G-CD4 responders (dashed lines) obtained from 10 different donors were cultured with 1.0 × 10⁵ irradiated (30 Gy) DR-mismatched allogeneic PBMC in round-bottom 96-well plates. Values for ³H-thymidine incorporation represent the mean cpm ± SEM from quadruplicate cultures with values from autologous background controls subtracted. (B) Proliferation of preG- and G-CD4 cells in response to immobilized CD3-specific IgM in the presence of IL-2. Different numbers (2.5, 1.25, and 0.625 × 10⁴) of preG-CD4 responders (solid lines) or G-CD4 responders (dashed lines) obtained from three donors were seeded into flat-bottom 96-well plates precoated with antibody 38.1 at a concentration of 3 μg/mL. Values for ³H-thymidine incorporation represent the mean cpm ± SEM for triplicate cultures.