Decreased Frequency of Intestinal Regulatory CD5+ B Cells in Colonic Inflammation

CD5+ B cells are a type of regulatory immune cells, though the involvement of this B cell subset in intestinal inflammation and immune regulation is not fully understood. We examined the distribution of CD5+ B cells in various mouse organs. Expression levels of CD11b, IgM, and toll-like receptor (TLR)-4 and -9 in B cells were evaluated. In vitro, TLR-stimulated IL-10 production by colonic lamina propria (LP) CD5+ and CD5- B cells was measured. In vivo, mice with acute or chronic dextran sulfate sodium (DSS)-induced colonic injury were examined, and the frequency of colonic LP CD5+ B cells in those was assessed by flow cytometry. The expression level of TLR9 was higher in colonic LP CD5+ B cells as compared to CD5- B cells. Colonic LP CD5+ B cells produced greater amounts of IL-10 following stimulation with TLR ligands, especially TLR9, as compared with the LP CD5- B cells. Acute intestinal inflammation transiently decreased the frequency of colonic LP CD5+ B cells, while chronic inflammation induced a persistent decrease in colonic LP CD5+ B cells and led to a CD5- B cell-dominant condition. A persistent altered mucosal B cell population caused by chronic gut inflammation may be involved in the pathogenesis of inflammatory bowel diseases.