Figure 4. B cell subset composition of human GALT is distinct from LP.

(A-E) B cell populations in indicated tissues were assessed by flow cytometry. (A) Naïve IgD⁺CD19⁺ B cell frequency of total CD45⁺ cells. (B) CD20⁻CD38⁺ PC frequency of total CD45⁺ cells. (C) CD38⁻CD10^- memory B cell frequency amongst total CD45⁺ T cells. Each circle represents an individual donor, matched between each of the sites, with SM-ILF and M-ILF data from at least 5 pooled follicles. Bars, mean ± 1SD. (D–E) Representative contour plots (D) and frequency (E) of CD20^hiCD10⁺ GC B cells amongst total CD45⁺ cells. (F) CD20^hiCD10⁺ GC B cell frequency amongst total CD45⁺ cells in individual SM-ILF from 5 different donors. Each circle represents a single follicle. Bars, mean ± 1SD. (G) Whole-mount immunofluorescence stain of distal colon M-ILF and SM-ILF showing CD21⁺CD35⁺ follicular dendritic cells (green or yellow) within a CD19⁺ B cell follicle (red) surrounded by CD3⁺ T cells (white). Arrow depicts location of epithelium and star location of sub-epithelial dome. Scale bars, 100μm. (H and I) Expression of (H) AICDA and (I) SDC1 mRNA in indicated tissues as assessed by qPCR. Each circle represents a single follicle (PP or ILF) or LP sample (LP) and data are from 4 patients. Bars, mean ± 1SD. (J) B cell populations in indicated sites of the sigmoid colon. Each circle represents an individual donor with paired samples. SM-ILF and M-ILF data are from at least 5 pooled follicles per patient. Bars, mean ± 1SD. Pooled data of indicated Ig isotype expression by (K) GC and (L) memory B cells in PP, M-ILF and SM-ILF. Each circle represents an individual donor with lines joining paired samples. SM-ILF and M-ILF data are from least 5 pooled ILF per patient. Bars, mean ± 1SD. PP, Peyer’s patch; SM-ILF, submucosal follicle; M-ILF, mucosal follicle; LP, lamina propria. Statistical significance was determined using the paired Friedman test with Dunn’s multiple comparisons *p<0.05, **p<0.01, ***p<0.001. See also Figure S4.