We have investigated the influence of mast cells on the barrier function of intestinal epithelium during nematode infection. Trichinella spiralis infection induces a strong type 2 cytokinemediated inflammation, resulting in a critical mucosal mastocytosis that is known to mediate expulsion of the parasites from the intestine. The host response to infection is also characterized by an increase in mucosal leakiness. We show here that intestinal epithelial permeability is markedly elevated during infection, with kinetics that mirror the adaptive immune response to primary and secondary infection. Furthermore, we have identified degradation of the tight junction protein, occludin, thereby providing a mechanism for increased paracellular permeability during helminth infection. We further demonstrate by using anti-c-kit antibody and IL-9 transgenic mice that mast cells are directly responsible for increasing epithelial paracellular permeability and that mice deficient in a mast cell-specific protease fail to increase intestinal permeability and fail to expel their parasite burden. These results provide the mechanism whereby mucosal mast cells mediate parasite expulsion from the intestine.T he adult stage of the nematode Trichinella spiralis resides within enterocytes of the jejunum. During parasite infection characteristic changes occur in the small intestine (1). It has long been known that the gut becomes edematous and inflamed, with these responses peaking at the time of parasite expulsion from the host, but the precise mechanisms involved have remained obscure. Infection induces leakiness in the intestinal epithelium that is considered to be a host defense mechanism against the parasite (the leak-lesion hypothesis) (2).We hypothesize that an increase in epithelial paracellular permeability resulting in the loss of parasites is a direct consequence of adaptive immunity. T. spiralis elicits a strong T helper 2 response resulting in intestinal goblet cell hyperplasia, eosinophilia, and a profound mucosal mastocytosis (3-5). Efficient parasite expulsion depends on CD4 ϩ T cells through control of the critical mast cell response (6). In the absence of intestinal mast cells the loss of parasites is markedly delayed (7). The mechanism by which mast cells induce parasite expulsion is unknown and is the focus of this study.Changes in epithelial paracellular permeability during the course of T. spiralis infection in mice and the role that the mast cell may play in inducing these changes were investigated. By depleting mast cells with anti-c-kit antibodies or by using IL-9 transgenic mice that overexpress mast cells (8), we present compelling evidence that mast cells are the key mediators of increased mucosal permeability. To understand further the action of mast cells on intestinal epithelium, we have infected mice deficient in mouse mast cell protease-1 (mMCP-1) that had been shown previously to delay parasite expulsion (9) and investigated whether this mast cell-specific proteinase is involved in increased epithelial perm...

The ontogeny and function of gut‐associated‐lymphoid tissue is known to be critically dependent on the β7 integrin subfamily. We have investigated the development of intestinal inflammation and pathogen‐specific protective immunity to enteric helminth infection in β7 integrin knockout (KO) mice. During Trichinella spiralis infection of the small intestine there was a significant delay and reduction in the magnitude of intestinal eosinophilia and mastocytosis in the absence of β7 integrin, resulting in impaired host protection. Aberrant distribution of mast cells was also observed in the small intestine of infected KO mice. Adoptive transfer of primed wild‐type mesenteric lymph node cells into T. spiralis‐infected β7 KO mice did not restore the intestinal mast cell response, suggesting that the defect in intestinal mastocytosis is due to the absence of β7 expression on this population rather than an indirect consequence of reduced T cell numbers. In contrast, no impairment in leukocyte recruitment or protection against Trichuris muris infection of the large intestine was observed in KO mice. Taken together the data provide the first description of reduced leukocyte homing and attenuated protective immunity against helminth infection in β7 KO mice. Furthermore, these results suggest that β7 integrin‐independent adhesion molecule interactions are deployed in the large but not small intestine during intestinal inflammation.

IL-13 is a Th2-derived cytokine associated with pathological changes in asthma and ulcerative colitis. Moreover, it plays a major role in the control of gut nematode infection and associated immunopathology. The current paradigm is that these effects are due to T cell-derived IL-13. We show in this study that an innate source of IL-13, the intraepithelial NK cell, is responsible for the disruption of intestinal tissue architecture and induction of goblet cell hyperplasia that characterizes infection with the intestinal helminth Trichinella spiralis. IL-13 or IL-4Rα (but not IL-4) null mice failed to induce intestinal pathology. Unexpectedly, SCID and athymic mice developed the same pathology found in immunocompetent mice following infection. Moreover, immunodeficient mice expressed IL-13 in the intestine, and abnormal mucosal pathology was reduced by in vivo administration of a soluble IL-13 antagonist. IL-13 expression was induced in non-T intraepithelial CD3− NK cells. Epithelial cells expressed the IL-13 signaling receptor, IL-13Rα1, and after infection, IL-4Rα. Furthermore, the soluble IL-13 decoy receptor IL-13Rα2, which regulates IL-13 responses, was also induced upon infection. These data provide the first evidence that intestinal tissue restructuring during helminth infection is an innate event dependent on IL-13 production by NK cells resident in the epithelium of the intestine.

B cells are salient features of pancreatic ductal adenocarcinoma (PDAC) tumors, yet their role in this disease remains controversial. Murine studies have indicated a protumoral role for B cells, whereas clinical data show tumor-infiltrating B cells are a positive prognostic factor, both in PDAC and other cancers. This disparity needs to be clarified in order to develop effective immunotherapies. In this study, we provide new evidence that reconcile human and mouse data and highlight the importance of using relevant preclinical tumor models when assessing B cell function. We compared B cell infiltration and activation in both a genetic model of murine PDAC (KPC mouse) and an injectable orthotopic model. A pronounced B cell infiltrate was only observed in KPC tumors and correlated with T cell infiltration, mirroring human disease. In contrast, orthotopic tumors exhibited a relative paucity of B cells. Accordingly, KPC-derived B cells displayed markers of B cell activation (germinal center entry, B cell memory, and plasma cell differentiation) accompanied by significant intratumoral immunoglobulin deposition, a feature markedly weaker in orthotopic tumors. Tumor immunoglobulins, however, did not appear to form immune complexes. Furthermore, in contrast to the current paradigm that tumor B cells are immunosuppressive, when assessed as a bulk population, intratumoral B cells upregulated several proinflammatory and immunostimulatory genes, a distinctly different phenotype to that of splenic-derived B cells; further highlighting the importance of studying tumor-infiltrating B cells over B cells from secondary lymphoid organs. In agreement with the current literature, genetic deletion of B cells (μMT mice) resulted in reduced orthotopic tumor growth, however, this was not recapitulated by treatment with B-cell-depleting anti-CD20 antibody and, more importantly, was not observed in anti-CD20-treated KPC mice. This suggests the result from B cell deficient mice might be caused by their altered immune system, rather than lack of B cells. Therefore, our data indicate B cells do not favor tumor progression. In conclusion, our analysis of relevant preclinical models shows B cells to be active members of the tumor microenvironment, producing immunostimulatory factors that might support the adaptive antitumor immune response, as suggested by human PDAC studies.