TNF hampers intestinal tissue repair in colitis by restricting IL-22 bioavailability.

Successful treatment of chronic inflammatory diseases integrates both the cessation of inflammation and the induction of adequate tissue repair processes. Strikingly, targeting a single proinflammatory cytokine, tumor necrosis factor (TNF), induces both processes in a relevant cohort of inflammatory bowel disease (IBD) patients. However, the molecular mechanisms underlying intestinal repair following TNF blockade during IBD remain elusive. Using a novel humanized model of experimental colitis, we demonstrate that TNF interfered with the tissue repair program via induction of a soluble natural antagonist of IL-22 (IL-22Ra2; IL-22BP) in the colon and abrogated IL-22/STAT3-mediated mucosal repair during colitis. Furthermore, membrane-bound TNF expressed by T cells perpetuated colonic inflammation, while soluble TNF produced by epithelial cells (IECs) induced IL-22BP expression in colonic dendritic cells (DCs) and dampened IL-22-driven restitution of colonic epithelial functions. Finally, TNF induced IL-22BP expression in human monocyte-derived DCs and levels of IL22-BP correlated with TNF in sera of IBD patients. Thus, our data can explain how anti-TNF therapy induces mucosal healing by increasing IL-22 availability and implicates new therapeutic opportunities for IBD.

Novel mouse model to study T cell-dependent IgA induction in vivo.

Commensal microbiota at the mucosal surfaces controls multiple aspects of body homeostasis. Therefore, regulation of microflora composition by the host is crucial, and one of the mechanisms driving microbiota diversity is the production of large quantities of immunoglobulin A (IgA) at the mucosal surfaces. However, mechanisms of IgA induction in the gut are not completely understood. Here we further characterize a mouse model for studying T cell-dependent IgA production in the gut due to specific genetic ablation of LTß in RORγt+ cells. Using in utero blockade of the mesenteric lymph node development, we showed that IgA induction in these mice occurs directly in the LP. Furthermore, T cell-dependent IgA inducing mechanism in these mice generates distinct IgA plasma cells producing commensal microflora-binding IgA antibodies. Thus, this model represents a unique in vivo tool for the analysis of T cell-dependent IgA plasma cell generation and their antibody specificity.

Cellular sources of pathogenic and protective TNF and experimental strategies based on utilization of TNF humanized mice.

Over the years, tumor necrosis factor (TNF) has been implicated in the pathogenesis of various inflammatory conditions and TNF antagonists are highly efficient in treatment of multiple autoimmune diseases. However, it has been shown that various cellular sources of TNF exhibit distinct and non-redundant functions that can be either deleterious or beneficial. This suggests that systemic TNF blockade, in addition to neutralization of pathogenic TNF, may abrogate its protective functions, resulting in adverse effects. Here we review the data on cellular sources of pathogenic and protective TNF and then discuss an experimental system based on humanized mice to study the role of cell-type specific TNF ablation during various disease models for development of cell-type specific TNF blockade.

Regulation and migratory role of P-selectin ligands during intestinal inflammation.

Dendritic cells from mesenteric lymph nodes (MLN) can convert retinal to retinoic acid (RA), which promotes induction of the gut-specific homing receptor α4ß7. In contrast, priming within peripheral lymph nodes leads to upregulation of E- and P-selectin ligands (E- and P-lig). Apart from its α4ß7 promoting effect, RA was shown to suppress E- and P-lig induction in vitro. However, enhanced frequencies of P-lig(+) CD4(+) T cells were reported during intestinal inflammation. To understand this contradiction, we first determined whether location of intestinal inflammation, that is, ileitis or colitis, affects P-lig induction. Both conditions promoted P-lig expression on CD4(+) T cells; however, P-lig expressed on T cells facilitated Th1 cell recruitment only into the inflamed colon but not into inflamed small intestine induced by oral Toxoplasma gondii infection. A majority of P-lig(+)CD4(+) T cells found within MLN during intestinal inflammation co-expressed α4ß7 confirming their activation in the presence of RA. Mesenteric P-lig(+)CD4(+) cells co-expressed the 130 kDa isoform of CD43 which requires activity of core 2 (beta)1,6-N-acetyl-glycosaminyltransferase-I (C2GlcNAcT-I) suggesting that C2GlcNAcT-I contributes to P-lig expression under these conditions. To test whether inflammatory mediators can indeed overrule the inhibitory effect of RA on P-lig expression we stimulated CD4(+) T cells either polyclonal in the presence of IL-12 and IFNγ or by LPS-activated MLN-derived dendritic cells. Both conditions promoted P-lig induction even in the presence of RA. While RA impeded the induction of fucosyltransferase-VII it did not affect IL-12-dependent C2GlcNAcT-I induction suggesting that C2GlcNAcT-I can support P-lig expression even if fucosyltransferase-VII mRNA upregulation is dampened.

Nonredundant function of soluble LTα3 produced by innate lymphoid cells in intestinal homeostasis.

Immunoglobulin A (IgA) production at mucosal surfaces contributes to protection against pathogens and controls intestinal microbiota composition. However, mechanisms regulating IgA induction are not completely defined. We show that soluble lymphotoxin α (sLTα3) produced by RORγt(+) innate lymphoid cells (ILCs) controls T cell-dependent IgA induction in the lamina propria via regulation of T cell homing to the gut. By contrast, membrane-bound lymphotoxin ß (LTα1ß2) produced by RORγt(+) ILCs is critical for T cell-independent IgA induction in the lamina propria via control of dendritic cell functions. Ablation of LTα in RORγt(+) cells abrogated IgA production in the gut and altered microbiota composition. Thus, soluble and membrane-bound lymphotoxins produced by ILCs distinctly organize adaptive immune responses in the gut and control commensal microbiota composition.