Fig 1: Human PC-Ms Accumulate in the Gut together with ME-M B Cells and Include a Circulating Counterpart Expressing Gut-Homing Receptors(A) Flow cytometry (FCM) of IgM and IgA on CD19+CD38hiCD10- PCs from human ileum and colon.(B) Frequency of PC-Ms among total PCs, assessed by FCM.(C) FCM of selected surface molecules on naive (N) B cells, PC-Ms, and switched PCs (PC-SW) from human ileum. Numbers indicate mean fluorescence intensity (MFI).(D) Immunofluorescence analysis (IFA) of IgM (green), IgA (red), and DNA (blue) in human ileum and mouse small intestine (SI) lamina propria (LP). Original magnification, 20×. Scale bars, 50 µm.(E) Number of PC-Ms (top), PC-As (center) per mm2 of LP, and PC-M/PC-A ratio (bottom) from human or mouse SI assessed following tissue IFA. Data summarize six different tissue samples where at least four high-power microscopic fields were analyzed.(F and G) Representative FCM (F) and frequency (G) of ß7+CCR9+ cells in human circulating PC-Ms, PC-As, and PC-G/Es.(H) Representative FCM showing IgM versus IgD staining on CD19+CD38-CD10- B cells from different human tissues.(I) Frequency of ME-M B cells from tissues shown in (H).(J) FCM of IgD, CD24, CD27, and CD148 on naive, ME-M, and ME-SW B cells from ileum.Data show one representative result (A, F, H) of 12 (B), 8 (G), or 52 (I) experiments or are from one experiment of at least 3 with similar results (C, D, J). Results are presented as mean ± SEM; two-tailed unpaired Student’s t test (B and E) and one-way ANOVA with Tukey’s post hoc test (I). *p < 0.05, **p < 0.01, ***p < 0.001. See also Figure S1.