下村 泰代

According to the 'hygiene hypothesis', enhanced microbial exposure due to early childhood infections leads to a reduction of T(h)2-mediated allergic diseases and inflammatory bowel disease. To begin to elucidate the mechanisms underlying this hypothesis, we studied development of T(h)2-mediated colitis of the TCR alpha knockout (KO) mouse in both a specific pathogen-free (SPF) facility and a conventional (CV) facility. After more than five generations in each facility, TCR alpha KO mice kept in the CV facility developed dramatically less colitis than mice that were kept in the SPF facility. Surprisingly, the suppression of colitis in the CV facility correlated with a significant increase in natural IgM production by B-1 B cells. In contrast, B cell-deficient TCR alpha double-knockout (alpha mu DKO) mice maintained in the CV facility continued to develop severe colitis, strongly suggesting that B-1 B cells contributed to the suppression of colitis. Indeed, the adoptive transfer of B-1 B cells isolated from the peritoneal cavity of TCR alpha KO mice (SPF) into alpha mu DKO mice (CV) suppressed the development of colitis in the recipient mice. We conclude that B-1 cells play a regulatory role in T(h)2-mediated colitis under non-hygienic conditions, possibly by generating natural antibodies in response to microbial flora.

Over 80% of the body's activated B cells are located in mucosal sites, including the intestine. The intestine contains IgM(+) B cells, but these cells have not been characterized phenotypically or in terms of their developmental origins. We describe a previously unidentified and unique subset of immunoglobulin M+ B cells that present with an AA4.1(-)CD21(-)CD23(-) major histocompatibility complex class IIbright surface phenotype and are characterized by a low frequency of somatic hypermutation and the potential ability to produce interleukin-12p70. This B cell subset resides within the normal mucosa of the large intestine and expands in response to inflammation. Some of these intestinal B cells originate from the AA4.1(+) immature B2 cell pool in the steady state and are also recruited from the recirculating naive B cell pool in the context of intestinal inflammation. They develop in an antigen-independent and BAFF-dependent manner in the absence of T cell help. Expansion of these cells can be induced in the absence of the spleen and gut-associated lymphoid tissues. These results describe the existence of an alternative pathway of B cell maturation in the periphery that gives rise to a tissue-specific B cell subset.

Background & Aims: Dysregulated host/microbial interactions induce the development of colitis by activating deleterious acquired immune responses. Activation of CD4(+) T cells is mainly induced through signaling machinery associated with immunologic synapse (IS). A key molecule associated with the IS is protein kinase C (PKC) theta. However, the role of PKC theta in the pathogenesis of colitis has not fully been defined. Methods: The role of PKC theta for the acquired-immune responses involved in the development of different types of colitis (CD45RB model, T-cell receptor [TCR] alpha knockout [KO] mice and interleukin [IL]-2KO mice) was examined by generating double KO mice and by utilizing cell transfer approaches. Results: Adoptive transfer of PKC theta-deficient naive CD4+ T cells failed to induce T helper cell (Th) 1-mediated colitis in the immune-deficient host (CD45RB model). Development of Th2-mediated colitis in TCR alpha KO mice was also inhibited by the absence of PKC theta. In IL-2KO mice, which develop colitis because of dysregulated T-cell homeostasis, deficiency of PKC theta in CD4(+) T cells failed to induce the development of severe colitis. Interestingly, absence of PKC theta led to a remarkable decrease in the proliferation, but not apoptosis, of colonic memory CD4(+) T cells. This impaired proliferation resulted in a marked decrease in the colonic CD4(+) T cells that are capable of producing IL-17. In addition, deficiency of PKC theta inhibited the production of Th2 cytokines by colonic CD4(+) T cells. Conclusions: PKC theta serves as a common and fundamental signaling molecule in the development of different types of colitis and may represent an attractive target for treating inflammatory bowel disease.

Expression of IL-22 is induced in several human inflammatory conditions, including inflammatory bowel disease (IBD). Expression of the IL-22 receptor is restricted to innate immune cells; however, the role of IL-22 in colitis has not yet been defined. We developed what we believe to be a novel microinjection-based local gene-delivery system that is capable of targeting the inflamed intestine. Using this approach, we demonstrated a therapeutic potency for IL-22-mediated activation of the innate immune pathway in a mouse model of Th2-mediated colitis that induces disease with characteristics similar to that of IBD ulcerative colitis (UC). IL-22 gene delivery enhanced STAT3 activation specifically within colonic epithelial cells and induced both STAT3-dependent expression of mucus-associated molecules and restitution of mucus-producing goblet cells. Importantly, IL-22 gene delivery led to rapid amelioration of local intestinal inflammation. The amelioration of disease by IL-22 was mediated by enhanced mucus production. In addition, local gene delivery was used to inhibit IL-22 activity through overexpression of IL-22-binding protein. Treatment with IL-22-binding protein suppressed goblet cell restitution during the recovery phase of a dextran sulfate sodium-induced model of acute colitis. These data demonstrate what we believe to be a novel function for IL-22 in the intestine and suggest the potency of a local IL-22 gene-delivery system for treating UC.

Background & Aim: T-cell receptor (TCR) gamma delta T cells are an important component of the mucosal immune system and regulate intestinal epithelial homeostasis. Interestingly, there is a significant increase in gamma delta T cells in the inflamed mucosa of patients with ulcerative colitis (UC). However, the role of gamma delta T cells in chronic colitis has not been fully identified. Methods: TCR alpha-deficient mice, which spontaneously develop chronic colitis with many features of human UC including an increase in gamma delta T-cell population, represent an excellent model to investigate the role of gamma delta T cells in UC-like colitis. To identify the role of gamma delta T cells in this colitis, we herein have generated TCR gamma-deficient mice through deletion of all TCR C gamma genes (C gamma 1, C gamma 2, C gamma 3, and C gamma 4) using the Cre/loxP site-specific recombination system and subsequently crossing these mice with TCR alpha-deficient mice. Results: An increase in colonic gamma delta T cells was associated with the development of human UC as well as UC-like disease seen in TCR alpha-deficient mice. Interestingly, the newly established TCR alpha(-/-) x TCR gamma(-/-) double mutant mice developed significantly less severe colitis as compared with TCR alpha-deficient mice. The suppression of colitis in TCR alpha(-/-) x TCR gamma(-/-) double mutant mice was associated with a significant reduction of proinflammatory cytokine and chemokine productions and a decrease in neutrophil infiltration. Conclusions: gamma delta T cells are involved in the exacerbation of UC-like chronic disease. Therefore, gamma delta T cells may represent a promising therapeutic target for the treatment of human UC.