PC-specific IgM is produced by human CD27⁺ B cells upon IRAK-4– and MyD88-dependent TLR stimulation. (A) CD27⁺ B cells produce higher levels of total IgM and IgG when stimulated with TLR7 and TLR9 agonists. (B) PC-specific antibodies are produced by CD27⁺IgM⁺ B cells. Data from sorted PBMC samples derived from 6 unique individuals. (C) IRAK-4 and MyD88 deficiencies impair production of total and PC-specific IgM in response to TLR7 and TLR9 stimulation of PBMC cultures. Control (n = 4), IRAK-4/MyD88 deficient (n = 4). *P < .05, **P < .01, ***P < .001.