Plasma Cells in the Mucosa of Patients with Inflammatory Bowel Disease Produce Granzyme B and Possess Cytotoxic Activities

In both Crohn's disease (CD) and ulcerative colitis (UC), the gut is massively infiltrated with B cells and plasma cells, but the role of these cell types in the pathogenesis of gut tissue damage remains largely unknown. Human B cells express granzyme B (GrB) when cultured with IL-21, a cytokine overproduced in CD and UC mucosa. We therefore examined whether mucosal B cells express GrB and have cytotoxic activity in inflammatory bowel disease (IBD). GrB-expressing CD19(+) and IgA(+) cells were seen in the normal intestinal mucosa, but they were significantly more frequent in both CD and UC. In contrast, only a minority of CD19(+) and IgA(+) cells expressed perforin with no difference between IBD and controls. GrB-producing CD19(+) cells expressed CD27 and were CD38(high) and CD20 negative. CD19(+) B cells from IBD patients induced HCT-116 cell death. IL-21 enhanced GrB expression in control CD19(+) B cells and increased their cytotoxic activity. These data indicate that IBD-related inflammation is marked by mucosal accumulation of cytotoxic, GrB-expressing CD19(+) and IgA(+) cells, suggesting a role for these cells in IBD-associated epithelial damage.