Hyperexpression of FcγRI and Toll-like receptor 4 in the intestinal mast cells of Crohn’s disease patients

We previously reported that human mast cells (MCs) express high affinity IgG receptor (FcγRI) and Toll-like receptor 4 (TLR4) in response to interferon (IFN)-γ in vitro. The number of MCs is known to increase in Crohn’s disease (CD) and ulcerative colitis (UC). We aimed to examine the expression and function of the receptors in these diseases by immunohistochemistry of the colonic mucosae and by in vitro experiments. The density of MCs expressing FcγRI, TLR4, or both proteins was significantly higher in CD than in UC or control samples. The density of TNF-α+ MCs expressing FcγRI or TLR4 was significantly higher in CD than in control samples. LPS and IgG1 cross-linking synergistically induced a high level of TNF-α production in IFN-γ-treated human MCs. Hyperexpression of FcγRI and TLR4 on MCs was related to the high frequency of TNF-α expression in CD, suggesting the activation of MCs via these receptors in vivo.