Probes for INS

The atypical chemokine receptor 2 (ACKR2), also named D6, regulates local levels of inflammatory chemokines by internalization and degradation. To explore potential anti-inflammatory functions of ACKR2 in glomerulonephritis, we induced autologous nephrotoxic nephritis in C57/BL6 wild-type and Ackr2-deficient mice. Renal ACKR2 expression increased and localized to interstitial lymphatic endothelium during nephritis. At two weeks Ackr2–/–mice developed increased albuminuria and urea levels compared to wild-type mice. Histological analysis revealed increased structural damage in the glomerular and tubulointerstitial compartments within Ackr2−/− kidneys. This correlated with excessive renal leukocyte infiltration of CD4+ T cells and mononuclear phagocytes with increased numbers in the tubulointerstitium but not glomeruli in knockout mice. Expression of inflammatory mediators and especially markers of fibrotic tissue remodeling were increased along with higher levels of ACKR2 inflammatory chemokine ligands like CCL2 in nephritic Ackr2–/– kidneys. In vitro, Ackr2 deficiency in TNF-stimulated tubulointerstitial tissue but not glomeruli increased chemokine levels. These results are in line with ACKR2 expression in interstitial lymphatic endothelial cells, which also assures efflux of activated leukocytes into regional lymph nodes. Consistently, nephritic Ackr2–/– mice showed reduced adaptive cellular immune responses indicated by decreased regional T-cell activation. However, this did not prevent aggravated injury in the kidneys of Ackr2–/– mice with nephrotoxic nephritis due to simultaneously increased tubulointerstitial chemokine levels, leukocyte infiltration and fibrosis. Thus, ACKR2 is important in limiting renal inflammation and fibrotic remodeling in progressive nephrotoxic nephritis. Hence, ACKR2 may be a potential target for therapeutic interventions in immune complex glomerulonephritis.

Following renal ischemia-reperfusion injury (IRI) resolution of inflammation allows tubular regeneration, whereas ongoing inflammatory injury mediated by infiltrating leukocytes leads to nephron loss and renal fibrosis, typical hallmarks of chronic kidney disease. The atypical chemokine receptor 2 (ACKR2) is a chemokine decoy receptor, that binds and scavenges inflammatory CC-chemokines and reduces local leukocyte accumulation. We hypothesized that ACKR2 limits leukocyte infiltration, inflammation, and fibrotic tissue remodeling after renal IRI, thus preventing progression to chronic kidney disease. Compared to wild-type, Ackr2 deficiency increased CC chemokine ligand 2 levels in tumor necrosis factor-stimulated tubulointerstitial tissue in vitro. In Ackr2-deficient mice with early IRI one or five days after transient renal pedicle clamping tubular injury was similar to wild-type, although accumulation of mononuclear phagocytes increased in postischemic Ackr2-/-kidneys. Regarding long-term outcomes, Ackr2-/- kidneys displayed more tubular injury five weeks after IRI, which was associated with persistently increased renal infiltrates of mononuclear phagocytes, T cells, Ly6Chigh inflammatory macrophages, and inflammation. Moreover, Ackr2 deficiency resulted in substantially aggravated renal fibrosis in Ackr2-/- kidneys five weeks after IRI, as revealed by increased expression of matrix molecules, renal accumulation of αSMA+ myofibroblasts, and bone marrow-derived fibrocytes. ACKR2 plays an important role in limiting persistent inflammation, tubular loss, and renal fibrosis after ischemic acute kidney injury, and thus can prevent progression to chronic renal disease.

BACKGROUND:

Children with very early onset inflammatory bowel diseases (VEO-IBD) often have a refractory and severe disease course. A significant number of described VEO-IBD-causing monogenic disorders can be attributed to defects in immune-related genes. The diagnosis of the underlying primary immunodeficiency (PID) often has critical implications for the treatment of patients with IBD-like phenotypes.

METHODS:

To identify the molecular etiology in 5 patients from 3 unrelated kindred with IBD-like symptoms, we conducted whole exome sequencing. Immune workup confirmed an underlying PID.

RESULTS:

Whole exome sequencing revealed 3 novel CARMIL2 loss-of-function mutations in our patients. Immunophenotyping of peripheral blood mononuclear cells showed reduction of regulatory and effector memory T cells and impaired B cell class switching. The T cell proliferation and activation assays confirmed defective responses to CD28 costimulation, consistent with CARMIL2 deficiency.

CONCLUSION:

Our study highlights that human CARMIL2 deficiency can manifest with IBD-like symptoms. This example illustrates that early diagnosis of underlying PID is crucial for the treatment and prognosis of children with VEO-IBD.

Interleukin-22 (IL-22)-producing group 3 innate lymphoid cells (ILC3) maintains gut homeostasis but can also promote inflammatory bowel disease (IBD). The regulation of ILC3-dependent colitis remains to be elucidated. Here we show that Foxp3 + regulatory T cells (Treg cells) prevented ILC3-mediated colitis in an IL-10-independent manner. Treg cells inhibited IL-23 and IL-1β production from intestinal-resident CX3CR1 + macrophages but not CD103 + dendritic cells. Moreover, Treg cells restrained ILC3 production of IL-22 through suppression of CX3CR1 + macrophage production of IL-23 and IL-1β. This suppression was contact dependent and was mediated by latent activation gene-3 (LAG-3)—an immune checkpoint receptor—expressed on Treg cells. Engagement of LAG-3 on MHC class II drove profound immunosuppression of CX3CR1+ tissue-resident macrophages. Our study reveals that the health of the intestinal mucosa is maintained by an axis driven by Treg cells communication with resident macrophages that withhold inflammatory stimuli required for ILC3 function.