CD19⁻ PCs produce vaccine/pathogen-specific antibodies. (A) Bone marrow aspirate cells from healthy donors were sorted into 4 populations (CD19⁺ PCs, CD19⁻ PCs, B cells, and Dump⁺) and were analyzed by ELISPOT. (B) Total IgG, tetanus toxoid–, measles-, or mumps-specific IgG-producing cells were enumerated by ELISPOT. Each symbol represents an individual donor. Means and standard deviations are indicated. For total IgG, all pairwise comparisons demonstrated a P value of .0625 except CD19⁺ PC vs CD19⁻ PC and B cells vs Dump. For tetanus toxoid, all pairwise comparisons demonstrated a P value of .0625 except B cells vs Dump. For measles, only CD19⁺ PC vs B cells and CD19⁺ vs Dump comparisons demonstrated a P value of .0625. P values for all other pairwise comparisons were .1088 or greater (Wilcoxon signed-rank test). ASC, antibody-secreting cells.