Possible involvement of the interleukin-15 and interleukin-15 receptor system in a heightened state of lamina propria B cell activation and differentiation in patients with inflammatory bowel disease

Background. We investigated the possible roles of the interleukin (IL)-15 and IL-15 receptor (IL-15R) system in a heightened state of B-cell activation and differentiation in intestinal mucosa with inflammatory bowel disease (IBD). Methods. The expression of IL-15 and IL-15R alpha mRNA and protein in inflamed colonic mucosal tissues with IBD, and in control tissues was examined by reverse transcriptase-polymerase chain reaction and immunohistological methods. The effects of recombinant (r)IL-15 on the expression of IL-15R alpha on lamina propria B cells and the production of immunoglobulin G (IgG) were analyzed in vitro, using lamina propria mononuclear cells (LPMCs) isolated from control tissues. Results. The intensity of IL-15 and IL-15R alpha. mRNA was greater in the mucosal tissues of patients with IBD, especially in those of patients with ulcerative colitis (UC), than in control tissues. Compared to control tissues, mononuclear cells positive for IL-15R alpha protein were observed in greater proportions in tissue sections from patients with IBD, especially in those from patients with UC, where IL-15R alpha protein was localized to CD20-positive B cells to a significant degree. There were increases in the proportions of IL-15R alpha-positive B cells and IgG-producing cells in rIL-15- or rCD40L-stimulated cultures of LPMCs, with stimulatory effects being greater in the presence of their combination. Conclusions. These data suggest that the IL45 and IL-15R system may play important roles in the activation and differentiation of lamina propria B cells in patients with IBD, especially in those with UC.