MHC restriction in allogeneic MLR (A) and PPD-induced T-cell stimulation (B) using CD38⁺⁺ plasma cells, CD38⁺ cells, BMMCs, and monocytes as antigen-presenting cells. The percentage (mean ± SD of 3 experiments) of inhibition induced by MoAb against HLA-DR (), HLA-ABC (□), and a mouse control IgG (▨) is shown.