(A) B cells from multiple subjects were sorted and then pooled into CD3−CD19+ B cell populations based on IgD, CD27, CD38, and CD24 expression. (B–E) Supernatant from cocultures of different combinations of MAIT cells from multiple subjects, THP-1 cells, and BL21 (100 MOI per THP-1 cell) were added to different populations of sort-purified B cells, each population containing 150,000 IgD+CD27− cells per well plus either no extra cells (B), 150,000 added IgD+CD27+CD38− cells (C), 150,000 added IgD-CD27+CD38− cells (D), or 150,000 IgD−CD27+CD38++ cells (E), and cultured for 7 d. After 7 d, B cells were assayed for the frequency of CD38++CD24− plasmablasts. Data are s ± sem, and representative of 2 independent experiments. Significance was determined by 1-way ANOVA using Tukey’s multiple comparisons test. ****P ≤ 0.00001.