Decreased production of interleukin-10 and transforming growth factor-β in Toll-like receptor-activated intestinal B cells in SAMP1/Yit mice

A unique subset of B cells expressing interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) plays an essential role in preventing inflammation and autoimmunity. We investigated the presence of this cell subset in intestines and its role in the pathogenesis of ileitis using SAMP1/Yit and age-matched control AKR/J mice. Mononuclear cells were isolated from mesenteric lymph nodes (MLNs) and the expressions of B220, CD1d, CD5, Toll-like receptor 4 (TLR4) and TLR9 in isolated cells were analysed. Purified B cells were stimulated with lipopolysaccharide (LPS) or CpG-DNA, then IL-10 and TGF-beta(1) expressions were examined by enzyme immunoassay and flow cytometry. Production of IL-1 beta by TLR-mediated macrophages co-cultured with or without purified MLN B cells from SAMP1/Yit and AKR/J mice was evaluated. In addition, interferon-gamma (IFN-gamma) production in intestinal T cells co-cultured with MLN B cells were also assessed in SAMP1/Yit and AKR/J strains. The production levels of IL-10 and TGF-beta(1) stimulated by LPS and CpG-DNA were significantly lower in B cells separated from MLNs from the SAMP1/Yit strain. B cells expressing IL-10 and TGF-beta(1) were mainly located in a population characterized by the cell surface marker CD1d(+). Interleukin-1 beta production by TLR-activated macrophages co-cultured with MLN B cells from SAMP1/Yit mice was significantly higher than that of those from AKR/J mice. Interestingly, IFN-gamma production by T cells was noted only when they were co-cultured with SAMP1/Yit but not the AKR/J B cells. These results are the first to show that disorders of regulatory B-cell function under innate immune activation may cause disease pathogenesis in a murine model of Crohn's disease.