IL-23 is essential for T cell-mediated colitis and promotes inflammation via IL-17 and IL-6.

Uncontrolled mucosal immunity in the gastrointestinal tract of humans results in chronic inflammatory bowel disease (IBD), such as Crohn disease and ulcerative colitis. In early clinical trials as well as in animal models, IL-12 has been implicated as a major mediator of these diseases based on the ability of anti-p40 mAb treatment to reverse intestinal inflammation. The cytokine IL-23 shares the same p40 subunit with IL-12, and the anti-p40 mAbs used in human and mouse IBD studies neutralized the activities of both IL-12 and IL-23. IL-10-deficient mice spontaneously develop enterocolitis. To determine how IL-23 contributes to intestinal inflammation, we studied the disease susceptibility in the absence of either IL-23 or IL-12 in this model, as well as the ability of recombinant IL-23 to exacerbate IBD induced by T cell transfer. Our study shows that in these models, IL-23 is essential for manifestation of chronic intestinal inflammation, whereas IL-12 is not. A critical target of IL-23 is a unique subset of tissue-homing memory T cells, which are specifically activated by IL-23 to produce the proinflammatory mediators IL-17 and IL-6. This pathway may be responsible for chronic intestinal inflammation as well as other chronic autoimmune inflammatory diseases.

Accelerated alveolar bone loss in mice lacking interleukin-10: late onset.

OBJECTIVE AND BACKGROUND: Interleukin-10 (IL-10) is an anti-inflammatory cytokine regulating immune responses. We have previously reported that IL-10(-/-) mice experience accelerated alveolar bone loss. The purpose of the present study was to examine the timing of the manifestation of accelerated alveolar bone loss in IL-10(-/-) mice. MATERIALS AND METHODS: Twenty-four IL-10(-/-) and 21 IL-10(+/+) age-matched male 129/SvEv mice were used. Sacrifice times occurred at 1, 3 and 9.5 months of age. Alveolar bone loss was determined morphometrically on defleshed jaws. Enzyme-linked immunosorbent assay (ELISA) was used for determination of serum concentration of type I collagen C-telopeptide, a systemic marker of bone resorption. RESULTS: Alveolar bone loss for the entire IL-10(-/-) group was significantly different than for the IL-10(+/+) group (p = 0.025). There was no significant difference in alveolar bone loss between IL-10(-/-) and IL-10(+/+) mice at 1 and 3 months of age. At 9.5 months of age, IL-10(-/-) mice exhibited 39% greater alveolar bone loss than IL-10(+/+) mice (p = 0.018). For IL-10(-/-) mice, alveolar bone loss significantly increased with age. Serum C-telopeptide levels significantly decreased with age in both groups. IL-10(-/-) mice had consistently higher C-telopeptide levels than IL-10(+/+) mice and the difference between the two groups reached statistical significance (p = 0.011) for the 9.5-month-old mice. CONCLUSIONS: These results suggest that the accelerated alveolar bone loss observed in IL-10(-/-) mice is a late-onset condition and that lack of IL-10 may have an effect on bone homeostasis.

IL-23 provides a limited mechanism of resistance to acute toxoplasmosis in the absence of IL-12.

IL-23 and IL-12 are heterodimeric cytokines which share the p40 subunit, but which have unique second subunits, IL-23p19 and IL-12p35. Since p40 is required for the development of the Th1 type response necessary for resistance to Toxoplasma gondii, studies were performed to assess the role of IL-23 in resistance to this pathogen. Increased levels of IL-23 were detected in mice infected with T. gondii and in vitro stimulation of dendritic cells with this pathogen resulted in increased levels of mRNA for this cytokine. To address the role of IL-23 in resistance to T. gondii, mice lacking the p40 subunit (common to IL-12 and IL-23) and mice that lack IL-12 p35 (specific for IL-12) were infected and their responses were compared. These studies revealed that p40(-/-) mice rapidly succumbed to toxoplasmosis, while p35(-/-) mice displayed enhanced resistance though they eventually succumbed to this infection. In addition, the administration of IL-23 to p40(-/-) mice infected with T. gondii resulted in a decreased parasite burden and enhanced resistance. However, the enhanced resistance of p35(-/-) mice or p40(-/-) mice treated with IL-23 was not associated with increased production of IFN-gamma. When IL-23p19(-/-) mice were infected with T. gondii these mice developed normal T cell responses and controlled parasite replication to the same extent as wild-type mice. Together, these studies indicate that IL-12, not IL-23, plays a dominant role in resistance to toxoplasmosis but, in the absence of IL-12, IL-23 can provide a limited mechanism of resistance to this infection.

A receptor for the heterodimeric cytokine IL-23 is composed of IL-12Rbeta1 and a novel cytokine receptor subunit, IL-23R.

IL-23 is a heterodimeric cytokine composed of the IL-12p40 "soluble receptor" subunit and a novel cytokine-like subunit related to IL-12p35, termed p19. Human and mouse IL-23 exhibit some activities similar to IL-12, but differ in their capacities to stimulate particular populations of memory T cells. Like IL-12, IL-23 binds to the IL-12R subunit IL-12Rbeta1. However, it does not use IL-12Rbeta2. In this study, we identify a novel member of the hemopoietin receptor family as a subunit of the receptor for IL-23, "IL-23R." IL-23R pairs with IL-12Rbeta1 to confer IL-23 responsiveness on cells expressing both subunits. Human IL-23, but not IL-12, exhibits detectable affinity for human IL-23R. Anti-IL-12Rbeta1 and anti-IL-23R Abs block IL-23 responses of an NK cell line and Ba/F3 cells expressing the two receptor chains. IL-23 activates the same Jak-stat signaling molecules as IL-12: Jak2, Tyk2, and stat1, -3, -4, and -5, but stat4 activation is substantially weaker and different DNA-binding stat complexes form in response to IL-23 compared with IL-12. IL-23R associates constitutively with Jak2 and in a ligand-dependent manner with stat3. The ability of cells to respond to IL-23 or IL-12 correlates with expression of IL-23R or IL-12Rbeta2, respectively. The human IL-23R gene is on human chromosome 1 within 150 kb of IL-12Rbeta2.

IL-27, a heterodimeric cytokine composed of EBI3 and p28 protein, induces proliferation of naive CD4+ T cells.

An efficient Th1-driven adaptive immune response requires activation of the T cell receptor and secretion of the T cell stimulatory cytokine IL-12 by activated antigen-presenting cells. IL-12 triggers Th1 polarization of naive CD4(+) T cells and secretion of IFN-gamma. We describe a new heterodimeric cytokine termed IL-27 that consists of EBI3, an IL-12p40-related protein, and p28, a newly discovered IL-12p35-related polypeptide. IL-27 is an early product of activated antigen-presenting cells and drives rapid clonal expansion of naive but not memory CD4(+) T cells. It also strongly synergizes with IL-12 to trigger IFN-gamma production of naive CD4(+) T cells. IL-27 mediates its biologic effects through the orphan cytokine receptor WSX-1/TCCR.