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 13-cell activation and differentiation in intestinal mucosa with inflammatory bowel disease (IBD). Methods. The expression of IL-15 and IL-15Rα 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-15Rα 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-15Rα 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 con- trol tissues, mononuclear cells positive for IL-15Rα protein were observed in greater proportions in tissue sections from patients with IBD), especially in those from patients with UC, where IL-15Rα protein was localized to CD20-positive B cells to a significant degree. There were increases in the proportions of IL-15Rα-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 IL-15 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. [ABSTRACT FROM AUTHOR]