Innate immune cells in acute and chronic kidney disease

Acute kidney injury (AKI) and chronic kidney disease (CKD) are inter-related clinical and pathophysiological disorders. Cells of the innate immune system, such as granulocytes and macrophages, can induce AKI through the secretion of pro-inflammatory mediators such as cytokines, chemokines and enzymes, and the release of extracellular traps. In addition, macrophages and dendritic cells can drive the progression of CKD through a wide range of pro-inflammatory and pro-fibrotic mechanisms, and by regulation of the adaptive immune response. However, innate immune cells can also promote kidney repair after acute injury. These actions highlight the multifaceted nature of the way by which innate immune cells respond to signals within the kidney microenvironment, including interaction with the complement and coagulation cascades, cells of the adaptive immune system, intrinsic renal cells and infiltrating mesenchymal cells. The factors and mechanisms that underpin the ability of innate immune cells to contribute to renal injury or repair and to drive the progression of CKD are of great interest for understanding disease processes and for developing new therapeutic approaches to limit AKI and the AKI-to-CKD transition.

Kidney immunology from pathophysiology to clinical translation

Kidney diseases are widespread and represent a considerable medical, social and economic burden. However, there has been marked progress in understanding the immunological aspects of kidney disease. This includes the identification of distinct intrarenal immunological niches and characterization of kidney disease endotypes according to the underlying molecular immunopathology, as well as a better understanding of the pathological roles for T cells, mononuclear phagocytes and B cells and the renal elements they target. These insights have improved the diagnosis of kidney disease. Here, we discuss new developments in our understanding of kidney immunology, focusing on immune mechanisms of disease and their translational implications for the diagnosis and treatment of kidney disease. We also describe the immune-mediated crosstalk between the kidney and other organs that influences kidney disease and extrarenal inflammation.

Disease associations of natural killer (NK) cell KIR gene content variation in 352,783 Finns

Allelic, gene presence/absence, and gene-copy number variations in the KIR genes encoding Natural Killer (NK) cell surface receptors have been reported to be associated in case-control studies with infectious and autoimmune diseases, and relapse after stem cell transplantation. To understand more comprehensively the role of KIR gene presence/absence variation and HLA-KIR interactions in disease susceptibility, we imputed from genome SNP data the presence and absence of 10 KIR genes in the FinnGen cohort. The cohort consists of 352,783 Finns with extensive phenotypes from the national health registries. We tested associations between 762 FinnGen phenotypes and presence/absence variation based on imputation of KIR genes using 5,900 SNPs located in the KIR genomic segment. Our results provide a platform to query HLA-KIR associations in a large population cohort. We found 13 phenotype - KIR gene or KIR - HLA C combination associations with false discovery rate < 0.05. These results differ from the very high number of associations between HLA alleles and diseases reported earlier in the FinnGen cohort. Five of the 13 significant associations included malignant phenotypes, e.g., melanoma, thyroid gland neoplasm, and haematopoietic malignancy, supporting the essential role of NK cells in controlling malignancy.

Metalloporphyrins as Tools for Deciphering the Role of Heme Oxygenase in Renal Immune Injury

Renal immune injury is a frequent cause of end-stage renal disease, and, despite the progress made in understanding underlying pathogenetic mechanisms, current treatments to preserve renal function continue to be based mainly on systemic immunosuppression. Small molecules, naturally occurring biologic agents, show considerable promise in acting as disease modifiers and may provide novel therapeutic leads. Certain naturally occurring or synthetic Metalloporphyrins (Mps) can act as disease modifiers by increasing heme oxygenase (HO) enzymatic activity and/or synthesis of the inducible HO isoform (HO-1). Depending on the metal moiety of the Mp employed, these effects may occur in tandem or can be discordant (increased HO-1 synthesis but inhibition of enzyme activity). This review discusses effects of Mps, with varying redox-active transitional metals and cyclic porphyrin cores, on mechanisms underlying pathogenesis and outcomes of renal immune injury.

Low-Dose rIL-15 Protects from Nephrotoxic Serum Nephritis via CD8+ T Cells

Rapid progressive glomerulonephritis (GN) often leads to end-stage kidney disease, driving the need for renal replacement therapy and posing a global health burden. Low-dose cytokine-based immunotherapies provide a new strategy to treat GN. IL-15 is a strong candidate for the therapy of immune-mediated kidney disease since it has proven to be tubular-protective before. Therefore, we set out to test the potential of low-dose rIL-15 treatment in a mouse model of nephrotoxic serum nephritis (NTS), mimicking immune complex-driven GN in humans. A single low-dose treatment with rIL-15 ameliorated NTS, reflected by reduced albuminuria, less tissue scarring, fewer myeloid cells in the kidney, and improved tubular epithelial cell survival. In addition, CD8⁺ T cells, a primary target of IL-15, showed altered gene expression and function corresponding with less cytotoxicity mediated by rIL-15. With the use of transgenic knock-out mice, antibody depletion, and adoptive cell transfer studies, we here show that the beneficial effects of rIL-15 treatment in NTS depended on CD8⁺ T cells, suggesting a pivotal role for them in the underlying mechanism. Our findings add to existing evidence of the association of IL-15 with kidney health and imply a potential for low-dose rIL-15 immunotherapies in GN.