Mucosal-associated invariant T cells contribute to suppression of inflammatory myeloid cells in immune-mediated kidney disease.

Mucosal-associated invariant T (MAIT) cells have been implicated in various inflammatory diseases of barrier organs, but so far, their role in kidney disease is unclear. Here we report that MAIT cells that recognize their prototypical ligand, the vitamin B2 intermediate 5-OP-RU presented by MR1, reside in human and mouse kidneys. Single cell RNAseq analysis reveals several intrarenal MAIT subsets, and one, carrying the genetic fingerprint of tissue-resident MAIT17 cells, is activated and expanded in a murine model of crescentic glomerulonephritis (cGN). An equivalent subset is also present in kidney biopsies of patients with anti-neutrophil cytoplasmatic antibody (ANCA)-associated cGN. MAIT cell-deficient MR1 mice show aggravated disease, whereas B6-MAITCAST mice, harboring higher MAIT cell numbers, are protected from cGN. The expanded MAIT17 cells express anti-inflammatory mediators known to suppress cGN, such as CTLA-4, PD-1, and TGF-ß. Interactome analysis predicts CXCR6 - CXCL16-mediated cross-talk with renal mononuclear phagocytes, known to drive cGN progression. In line, we find that cGN is aggravated upon CXCL16 blockade. Finally, we present an optimized 5-OP-RU synthesis method which we apply to attenuating cGN in mice. In summary, we propose that CXCR6+ MAIT cells might play a protective role in cGN, implicating them as a potential target for anti-inflammatory therapies.

Retinoic acid drives intestine-specific adaptation of effector ILC2s originating from distant sites.

Adaptation of immune cells to tissue-specific microenvironments is a crucial process in homeostasis and inflammation. Here, we show that murine effector type 2 innate lymphoid cells (ILC2s) from various organs are equally effective in repopulating ILC2 niches in other anatomical locations where they adapt tissue-specific phenotypes of target organs. Single-cell transcriptomics of ILC2 populations revealed upregulation of retinoic acid (RA) signaling in ILC2s during adaptation to the small intestinal microenvironment, and RA signaling mediated reprogramming of kidney effector ILC2s toward the small intestinal phenotype in vitro and in vivo. Inhibition of intestinal ILC2 adaptation by blocking RA signaling impaired worm expulsion during Strongyloides ratti infection, indicating functional importance of ILC2 tissue imprinting. In conclusion, this study highlights that effector ILC2s retain the ability to adapt to changing tissue-specific microenvironments, enabling them to exert tissue-specific functions, such as promoting control of intestinal helminth infections.

MAIT cells in immune-mediated tissue injury and repair.

Mucosal-associated invariant T (MAIT) cells are T cells that express a semi-invariant αß T-cell receptor (TCR), recognizing non-peptide antigens, such as microbial-derived vitamin B2 metabolites, presented by the nonpolymorphic MHC class I related-1 molecule. Like NKT cells and γδT cells, MAIT cells belong to the group of innate-like T cells that combine properties of the innate and adaptive immune systems. They account for up to 10% of the blood T-cell population in humans and are particularly abundant at mucosal sites. Beyond the emerging role of MAIT cells in antibacterial and antiviral defenses, increasing evidence suggests additional functions in noninfectious settings, including immune-mediated inflammatory diseases and tissue repair. Here, we discuss recent advances in the understanding of MAIT cell functions in sterile tissue inflammation, with a particular focus on autoimmunity, chronic inflammatory diseases, and tissue repair.

GroEL is an immunodominant surface-exposed antigen of Rickettsia typhi.

Rickettsioses are neglected and emerging potentially fatal febrile diseases that are caused by obligate intracellular bacteria, rickettsiae. Rickettsia (R.) typhi and R. prowazekii constitute the typhus group (TG) of rickettsiae and are the causative agents of endemic and epidemic typhus, respectively. We recently generated a monoclonal antibody (BNI52) against R. typhi. Characterization of BNI52 revealed that it specifically recognizes TG rickettsiae but not the members of the spotted fever group (SFG) rickettsiae. We further show that BNI52 binds to protein fragments of ±30 kDa that are exposed on the bacterial surface and also present in the periplasmic space. These protein fragments apparently derive from the cytosolic GroEL protein of R. typhi and are also recognized by antibodies in the sera from patients and infected mice. Furthermore, BNI52 opsonizes the bacteria for the uptake by antigen presenting cells (APC), indicating a contribution of GroEL-specific antibodies to protective immunity. Finally, it is interesting that the GroEL protein belongs to 32 proteins that are differentially downregulated by R. typhi after passage through immunodeficient BALB/c CB17 SCID mice. This could be a hint that the rickettsia GroEL protein may have immunomodulatory properties as shown for the homologous protein from several other bacteria, too. Overall, the results of this study provide evidence that GroEL represents an immunodominant antigen of TG rickettsiae that is recognized by the humoral immune response against these pathogens and that may be interesting as a vaccine candidate. Apart from that, the BNI52 antibody represents a new tool for specific detection of TG rickettsiae in various diagnostic and experimental setups.

Interleukin-9 protects from early podocyte injury and progressive glomerulosclerosis in Adriamycin-induced nephropathy.

A wide spectrum of immunological functions has been attributed to Interleukin 9 (IL-9), including effects on the survival and proliferation of immune and parenchymal cells. In recent years, emerging evidence suggests that IL-9 expression can promote tissue repair in inflammatory conditions. However, data about the involvement of IL-9 in kidney tissue protection is very limited. Here, we investigated the role of IL-9 in Adriamycin-induced nephropathy (AN), a mouse model for proteinuric chronic kidney disease. Compared to wild type mice, IL-9 knockout (Il9-/-) mice with AN displayed accelerated development of proteinuria, aggravated glomerulosclerosis and deterioration of kidney function. At an early stage of disease, the Il9-/- mice already displayed a higher extent of glomerular podocyte injury and loss of podocyte number compared to wild type mice. In the kidney, T cells and innate lymphoid cells produced IL-9. However, selective deficiency of IL-9 in the innate immune system in Il9-/-Rag2-/- mice that lack T and B cells did not alter the outcome of AN, indicating that IL-9 derived from the adaptive immune system was the major driver of tissue protection in this model. Mechanistically, we could show that podocytes expressed the IL-9 receptor in vivo and that IL-9 signaling protects podocytes from Adriamycin-induced apoptosis in vitro. Finally, in vivo treatment with IL-9 effectively protected wild type mice from glomerulosclerosis and kidney failure in the AN model. The detection of increased serum IL-9 levels in patients with primary focal and segmental glomerulosclerosis further suggests that IL-9 production is induced by glomerular injury in humans. Thus, IL-9 confers protection against experimental glomerulosclerosis, identifying the IL-9 pathway as a potential therapeutic target in proteinuric chronic kidney disease.

Endogenous IL-22 is dispensable for experimental glomerulonephritis.

In recent years, the cytokine interleukin (IL)-22 attracted considerable attention due to its important immunoregulatory function in barrier tissues, such as the gut, lung, and skin. Although a regenerative role of IL-22 in renal tubular damage has been demonstrated, the role of IL-22 in the immunopathogenesis of glomerular injury is still unknown. Here, we demonstrate that the IL-22 receptor is expressed in the glomerular compartment of the kidney and that IL-22 expression increases in the renal cortex after induction of glomerular injury in a mouse model for crescentic glomerulonephritis (cGN, nephrotoxic nephritis). We identified γδ T cells and TH17 cells as major sources for IL-22 in the nephritic kidney. However, neither genetic or antibody-mediated deletion of IL-22 nor genetic deficiency in its endogenous inhibitor IL-22Rα2 (IL-22 binding protein) resulted in substantial phenotypic differences in mice with cGN with respect to crescent formation, tubulointerstitial damage, and kidney function impairment. Similarly, we did not observe significant differences between wild-type or IL-22-deficient mice in a mouse model of secondary focal and segmental glomerulosclerosis (adriamycin-induced nephropathy). As shown previously, we detected concomitant upregulation of IL-17A and IFN-γ production by T cells during the course of cGN, providing alternative cytokine pathways that mediate glomerular injury in this model. In conclusion, we show here that endogenous IL-22 expression is redundant in different forms of glomerular injury, indicating that the IL-22-directed therapies that are being tested in various human diseases might not affect the kidney in patients with glomerular disease.

T cell-derived IFN-γ downregulates protective group 2 innate lymphoid cells in murine lupus erythematosus.

Innate lymphoid cells (ILCs) are important regulators of the immune response and play a crucial role in the restoration of tissue homeostasis after injury. GATA-3+ IL-13- and IL-5-producing group 2 innate lymphoid cells (ILC2s) have been shown to promote tissue repair in barrier organs, but despite extensive research on ILCs in the recent years, their potential role in autoimmune diseases is still incompletely understood. In the present study, we investigate the role of ILC2s in the MRL/MpJ-Faslpr (MRL-lpr) mouse model for severe organ manifestation of systemic lupus erythematosus (SLE). We show that in these MRL-lpr mice, progression of lupus nephritis is accompanied with a reduction of ILC2 abundance in the inflamed renal tissue. Proliferation/survival and cytokine production of kidney-residing ILC2s was suppressed by IFN-γ and, to a lesser extent, by IL-27 which were produced by activated T cells and myeloid cells in the nephritic kidney, respectively. Most importantly, restoration of ILC2 numbers by IL-33-mediated expansion ameliorated lupus nephritis and prevented mortality in MRL-lpr mice. In summary, we show here that development of SLE-like kidney inflammation leads to a downregulation of the renal ILC2 response and identify an ILC2-expanding therapy as a promising treatment approach for autoimmune diseases.