Infections by attaching and effacing (A/E) bacterial pathogens, such as Escherichia coli O157:H7, pose a serious threat to public health. Using a mouse A/E pathogen, Citrobacter rodentium, we show that interleukin-22 (IL-22) has a crucial role in the early phase of host defense against C. rodentium. Infection of IL-22 knockout mice results in increased intestinal epithelial damage, systemic bacterial burden and mortality. We also find that IL-23 is required for the early induction of IL-22 during C. rodentium infection, and adaptive immunity is not essential for the protective role of IL-22 in this model. Instead, IL-22 is required for the direct induction of the Reg family of antimicrobial proteins, including RegIIIbeta and RegIIIgamma, in colonic epithelial cells. Exogenous mouse or human RegIIIgamma substantially improves survival of IL-22 knockout mice after C. rodentium infection. Together, our data identify a new innate immune function for IL-22 in regulating early defense mechanisms against A/E bacterial pathogens.

Interleukin (IL)-17 is a pro-inflammatory cytokine that is produced by activated T cells. Despite increasing evidence that high levels of IL-17 are associated with several chronic inflammatory diseases including rheumatoid arthritis, psoriasis, and multiple sclerosis, the regulation of its expression is not well characterized. We observe that IL-17 production is increased in response to the recently described cytokine IL-23. We present evidence that murine IL-23, which is produced by activated dendritic cells, acts on memory T cells, resulting in elevated IL-17 secretion. IL-23 also induced expression of the related cytokine IL-17F. IL-23 is a heterodimeric cytokine and shares a subunit, p40, with IL-12. In contrast to IL-23, IL-12 had only marginal effects on IL-17 production. These data suggest that during a secondary immune response, IL-23 can promote an activation state with features distinct from the well characterized Th1 and Th2 profiles. Interleukin (IL)1 -17 is a T cell-derived pro-inflammatory molecule that stimulates epithelial, endothelial, and fibroblastic cells to produce other inflammatory cytokines and chemokines including IL-6, IL-8, G-CSF, and MCP-1 (1-8). IL-17 also synergizes with other cytokines including tumor necrosis factor-␣ and IL-1␤ to further induce chemokine expression (7, 9). Interleukin-17 levels are found to be significantly increased in rheumatoid arthritis synovium (10, 11), during allograft rejection (12-15), and in other chronic inflammatory diseases including multiple sclerosis (16) and psoriasis (17)(18)(19). Although clearly produced by activated T cells, previous reports have not provided clear classification of IL-17 within the paradigm of Th1 and Th2 polarized cytokine profiles.We have examined the possibility that IL-17 is expressed in response to signals distinct from those associated with the Th1 or Th2 response. We observe a previously unrecognized activity of the recently identified cytokine . IL-23 is a heterodimeric cytokine that shares one subunit, p40, with IL-12. The initial characterization of this cytokine has suggested it can promote proliferation within the memory T cell population. Subsequent work demonstrated that transgenic over-expression of the second component of IL-23, p19, was sufficient to induce systemic inflammation and premature death (21). In addition, the mice had markedly elevated levels of circulating neutrophils. Interestingly they did not exhibit consistent elevation of IFN-␥, a hallmark effect of IL-12. These data suggest that IL-23 may have a biological role substantially distinct from that of IL-12. In this report we present evidence that IL-23 acts to induce a distinct T cell activation state that produces IL-17 as a principle effector cytokine. EXPERIMENTAL PROCEDURESCell Culture-Single cell suspensions of spleen were prepared from C57/BL-6 mice, and mononuclear cells were isolated from suspended splenocytes by density gradient centrifugation. 2 ϫ 10 6 cells/ml were cultured with IL-2 (100 units/ml) in the presence or absence of vario...

Interleukin 27 (IL-27) was first characterized as a proinflammatory cytokine with T helper type 1-inducing activity. However, subsequent work has demonstrated that mice deficient in IL-27 receptor (IL-27R alpha) show exacerbated inflammatory responses to a variety of challenges, suggesting that IL-27 has important immunoregulatory functions in vivo. Here we demonstrate that IL-27R alpha-deficient mice were hypersusceptible to experimental autoimmune encephalomyelitis and generated more IL-17-producing T helper cells. IL-27 acted directly on effector T cells to suppress the development of IL-17-producing T helper cells mediated by IL-6 and transforming growth factor-beta. This suppressive activity was dependent on the transcription factor STAT1 and was independent of interferon-gamma. Finally, IL-27 suppressed IL-6-mediated T cell proliferation. These data provide a mechanistic explanation for the IL-27-mediated immune suppression noted in several in vivo models of inflammation.

The complement system serves an important role in clearance of pathogens, immune complexes, and apoptotic cells present in the circulation. Complement fragments deposited on the particle surface serve as targets for complement receptors present on phagocytic cells. Although Kupffer cells, the liver resident macrophages, play a dominant role in clearing particles in circulation, complement receptors involved in this process have yet to be identified. Here we report the identification and characterization of a Complement Receptor of the Immunoglobulin superfamily, CRIg, that binds complement fragments C3b and iC3b. CRIg expression on Kupffer cells is required for efficient binding and phagocytosis of complement C3-opsonized particles. In turn, Kupffer cells from CRIg-deficient mice are unable to efficiently clear C3-opsonized pathogens in the circulation, resulting in increased infection and mortality of the host. CRIg therefore represents a dominant component of the phagocytic system responsible for rapid clearance of C3-opsonized particles from the circulation.

Leptin and its receptor, obese receptor (OB-R), comprise an important signaling system for the regulation of body weight. Splice variants of OB-R mRNA encode proteins that differ in the length of their cytoplasmic domains. We cloned a long isoform of the wild-type leptin receptor that is preferentially expressed in the hypothalamus and show that it can activate signal transducers and activators of transcription (STAT)-3, and . A point mutation within the OB-R gene of diabetic (db) mice generates a new splice donor site that dramatically reduces expression of this long isoform in homozygous db/db mice. In contrast, an OB-R protein with a shorter cytoplasmic domain is present in both db/db and wild-type mice. We show that this short isoform is unable to activate the STAT pathway. These data provide further evidence that the mutation in OB-R causes the db/db phenotype and identify three STAT proteins as potential mediators of the anti-obesity effects of leptin.Leptin, the product of the obese (ob) gene, is a 16-kDa secreted protein primarily produced by adipocytes (1). There is a good correlation between the percentage of body fat and serum leptin levels suggesting that leptin production is regulated by the mass of adipocytes (2, 3). Leptin levels were normal or elevated in obese individuals (2, 4) arguing against a simple leptin deficiency as the cause of obesity in the majority of humans (5). Serum leptin concentrations increased under a fatty diet but failed to prevent weight gain (3). Therefore, insensitivity to the action of leptin appears to be a common mechanism in obese individuals and in several rodent models. This suggests that dysregulation at the level of the leptin receptor, the downstream signaling pathway, or an unknown modifying mechanism may constitute the basis for weight disorders. The crucial role of leptin and its receptor in obesity is well illustrated by two phenotypically very similar mutants obese (ob) and diabetes (db) (6). Mice homozygous for a loss of function mutation of ob display obesity, hyperglycemia, and insulin resistance resembling type II diabetes. Administration of recombinant leptin to ob mice corrected these abnormalities (7-9). Based on early parabiosis experiments it was expected that db would be caused by a mutation in the ob receptor (OB-R) (6).OB-R was cloned by virtue of its high affinity to leptin through an expression cloning strategy (10). The OB-R gene was mapped to the same 5-centimorgan interval on mouse chromosome 4 to which db had been localized (10). Surprisingly, no mutation in the coding region of OB-R cDNA of db/db mice was found and leptin binding sites were unaltered in db/db mice (10). However, the cloned mouse OB-R cDNA encoded a protein with a much shorter cytoplasmic domain than the human homologue, suggesting that a longer mouse isoform exists. We cloned this longer form of OB-R from wild-type mice and found that the mRNA for this isoform is dramatically reduced in db/db mice. A G to T mutation in db mice generates a new splice donor and su...