Characterization of kidney CD45intCD11bintF4/80+MHCII+CX3CR1+Ly6C- "intermediate mononuclear phagocytic cells"

Lymphocytes and innate immune cells in acute kidney injury and repair

Acute kidney injury (AKI) is a common and serious disease entity that affects native kidneys and allografts but for which no specific treatments exist. Complex intrarenal inflammatory processes driven by lymphocytes and innate immune cells have key roles in the development and progression of AKI. Many studies have focused on prevention of early injury in AKI. However, most patients with AKI present after injury is already established. Increasing research is therefore focusing on mechanisms of renal repair following AKI and prevention of progression from AKI to chronic kidney disease. CD4+ and CD8+ T cells, B cells and neutrophils are probably involved in the development and progression of AKI, whereas regulatory T cells, double-negative T cells and type 2 innate lymphoid cells have protective roles. Several immune cells, such as macrophages and natural killer T cells, can have both deleterious and protective effects, depending on their subtype and/or the stage of AKI. The immune system not only participates in injury and repair processes during AKI but also has a role in mediating AKI-induced distant organ dysfunction. Targeted manipulation of immune cells is a promising therapeutic strategy to improve AKI outcomes.

Distinguishing the effects of systemic CSF1R inhibition by PLX3397 on microglia and peripheral immune cells

Microglia, the primary immune cells of the central nervous system (CNS), are derived from the yolk sac and populate the brain during development. Once microglia migrate to the CNS, they are self-renewing and require CSF1R signaling for their maintenance. Pexidartinib (PLX3397, PLX), a small molecule inhibitor of the CSF1R, has been shown to effectively deplete microglia since microglial maintenance is CSF1R-dependent. There have, however, been several conflicting reports that have shown the potential off-target effects of PLX on peripheral immune cells particularly those of lymphoid origin. Given this controversy in the use of the PLX family of drugs, it has become important to ascertain to what extent PLX affects the peripheral immune profile in lymphoid (spleen, and bone marrow) and non-lymphoid (kidney, lungs, and heart) organs. PLX3397 chow treatment at 660 mg/kg for 7 days significantly reduced CD45+ macrophages, CX3CR1-GFP cells, CD11b+CD45intermediate cells, and P2RY12 expression in the brain. However, there were minimal effects on peripheral immune cells from both lymphoid and non-lymphoid organs except in the heart where there was a significant decrease in CD3+ cells, inflammatory and patrolling monocytes, and CD11b+Ly6G+ neutrophils. We then stimulated the immune system with 1 mg/kg of LPS which resulted in a significant reduction in the number of innate immune cells. In this context, PLX did not alter the cytokine profile in the serum and the brain of naïve mice but did so in the LPS-stimulated group resulting in a significant reduction in TNFα, IL-1α, IFN-γ and IL-1β. Furthermore, PLX did not alter locomotor activity in the open field test suggesting that microglia do not contribute to LPS-induced sickness behavior. Our results provide an assessment of immune cell populations with PLX3397 treatment on brain, lymphoid and non-lymphoid organs without and during LPS treatment that can serve as a resource for understanding consequences of such approaches.

T-cell receptor αβ+ double-negative T cells in the kidney are predominantly extravascular and increase in abundance in response to ischemia-reperfusion injury

T-cell receptor+ CD4- CD8- double-negative (DN) T cells are a population of T cells present in low abundance in blood and lymphoid organs, but enriched in various organs including the kidney. Despite burgeoning interest in these cells, studies examining their abundance in the kidney have reported conflicting results. Here we developed a flow cytometry strategy to clearly segregate DN T cells from other immune cells in the mouse kidney and used it to characterize their phenotype and response in renal ischemia-reperfusion injury (IRI). These experiments revealed that in the healthy kidney, most DN T cells are located within the renal parenchyma and exhibit an effector memory phenotype. In response to IRI, the number of renal DN T cells is unaltered after 24 h, but significantly increased by 72 h. This increase is not related to alterations in proliferation or apoptosis. By contrast, adoptive transfer studies indicate that circulating DN T cells undergo preferential recruitment to the postischemic kidney. Furthermore, DN T cells show the capacity to upregulate CD8, both in vivo following adoptive transfer and in response to ex vivo activation. Together, these findings provide novel insights regarding the phenotype of DN T cells in the kidney, including their predominant extravascular location, and show that increases in their abundance in the kidney following IRI occur in part as a result of increased recruitment from the circulation. Furthermore, the observation that DN T cells can upregulate CD8 in vivo has important implications for detection and characterization of DN T cells in future studies.

Effect of M2-like macrophages of the injured-kidney cortex on kidney cancer progression

Chronic kidney disease (CKD) affects kidney cancer patients' mortality. However, the underlying mechanism remains unknown. M2-like macrophages have pro-tumor functions, also exist in injured kidney, and promote kidney fibrosis. Thus, it is suspected that M2-like macrophages in injured kidney induce the pro-tumor microenvironment leading to kidney cancer progression. We found that M2-like macrophages present in the injured kidney promoted kidney cancer progression and induced resistance to anti-PD1 antibody through its pro-tumor function and inhibition of CD8⁺ T cell infiltration. RNA-seq revealed Slc7a11 was upregulated in M2-like macrophages. Inhibition of Slc7a11 with sulfasalazine inhibited the pro-tumor function of M2-like macrophages and synergized with anti-PD1 antibody. Moreover, SLC7A11-positive macrophages were associated with poor prognosis among kidney cancer patients. Collectively, this study dissects the characteristic microenvironment in the injured kidney that contributed to kidney cancer progression and anti-PD1 antibody resistance. This insight offers promising combination therapy with anti-PD1 antibody and macrophage targeted therapy.

The changing landscape of immune cells in the fetal mouse testis

Fetal testis growth involves cell influx and extensive remodeling. Immediately after sex determination in mouse, macrophages enable normal cord formation and removal of inappropriately positioned cells. This study provides new information about macrophages and other immune cells after cord formation in fetal testes, including their density, distribution, and close cellular contacts. C57BL6J mouse testes from embryonic day (E) 13.5 to birth (post-natal day 0; PND0), were examined using immunofluorescence, immunohistochemistry, and RT-qPCR to identify macrophages (F4/80, CD206, MHCII), T cells (CD3), granulocytes/neutrophils (Ly6G), and germ cells (DDX4). F4/80⁺ cells were the most abundant, comprising 90% of CD45⁺ cells at E13.5 and declining to 65% at PND0. Changes in size, shape, and markers (CD206 and MHCII) documented during this interval align with the understanding that F4/80⁺ cells have different origins during embryonic life. CD3⁺ cells and F4/80⁻/MHCII⁺ were absent to rare until PND0. Ly6G⁺ cells were scarce at E13.5 but increased robustly by PND0 to represent half of the CD45⁺ cells. These immunofluorescence data were in accord with transcript analysis, which showed that immune marker mRNAs increased with testis age. F4/80⁺ and Ly6G⁺ cells were frequently inside cords adjacent to germ cells at E13.5 and E15.5. F4/80⁺ cells were often in clusters next to other immune cells. Macrophages inside cords at E13.5 and E15.5 (F4/80^Hi/CD206⁺) were different from macrophages at PND0 (F4/80^Dim/CD206⁻), indicating that they have distinct origins. This histological quantification coupled with transcript information identifies new cellular interactions for immune cells in fetal testis morphogenesis, and highlights new avenues for studies of their functional significance.

Monocytes transition to macrophages within the inflamed vasculature via monocyte CCR2 and endothelial TNFR2

Monocytes undergo phenotypic and functional changes in response to inflammatory cues, but the molecular signals that drive different monocyte states remain largely undefined. We show that monocytes acquire macrophage markers upon glomerulonephritis and may be derived from CCR2+CX3CR1+ double-positive monocytes, which are preferentially recruited, dwell within glomerular capillaries, and acquire proinflammatory characteristics in the nephritic kidney. Mechanistically, the transition to immature macrophages begins within the vasculature and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells, findings that are recapitulated in vitro with monocytes cocultured with TNF-TNFR2–activated endothelial cells generating CCR2 ligands. Single-cell RNA sequencing of cocultures defines a CCR2-dependent monocyte differentiation path associated with the acquisition of immune effector functions and generation of CCR2 ligands. Immature macrophages are detected in the urine of lupus nephritis patients, and their frequency correlates with clinical disease. In conclusion, CCR2-dependent functional specialization of monocytes into macrophages begins within the TNF-TNFR2–activated vasculature and may establish a CCR2-based autocrine, feed-forward loop that amplifies renal inflammation.

A flow cytometry approach reveals heterogeneity in conventional subsets of murine renal mononuclear phagocytes

Mononuclear phagocytes (MNPs) participate in inflammation and repair after kidney injury, reflecting their complex nature. Dissection into refined functional subunits has been challenging and would benefit understanding of renal pathologies. Flow cytometric approaches are limited to classifications of either different MNP subsets or functional state. We sought to combine these two dimensions in one protocol that considers functional heterogeneity in each MNP subset. We identified five distinct renal MNP subsets based on a previously described strategy. In vitro polarization of bone marrow-derived macrophages (BMDM) into M1- and M2-like cells suggested functional distinction of CD86 + MHCII + CD206- and CD206 + cells. Combination of both distinction methods identified CD86 + MHCII + CD206- and CD206 + cells in all five MNP subsets, revealing their heterologous nature. Our approach revealed that MNP composition and their functional segmentation varied between different mouse models of kidney injury and, moreover, was dynamically regulated in a time-dependent manner. CD206 + cells from three analyzed MNP subsets had a higher ex vivo phagocytic capacity than CD86 + MHCII + CD206- counterparts, indicating functional uniqueness of each subset. In conclusion, our novel flow cytometric approach refines insights into renal MNP heterogeneity and therefore could benefit mechanistic understanding of renal pathology.

Chess Not Checkers: Complexities Within the Myeloid Response to the Acute Kidney Injury Syndrome

Immune dysregulation in acute kidney injury (AKI) is an area of intense interest which promises to enhance our understanding of the disease and how to manage it. Macrophages are a heterogeneous and dynamic population of immune cells that carry out multiple functions in tissue, ranging from maintenance to inflammation. As key sentinels of their environment and the major immune population in the uninjured kidney, macrophages are poised to play an important role in the establishment and pathogenesis of AKI. These cells have a profound capacity to orchestrate downstream immune responses and likely participate in skewing the kidney environment toward either pathogenic inflammation or injury resolution. A clear understanding of macrophage and myeloid cell dynamics in the development of AKI will provide valuable insight into disease pathogenesis and options for intervention. This review considers evidence in the literature that speaks to the role and regulation of macrophages and myeloid cells in AKI. We also highlight barriers or knowledge gaps that need to be addressed as the field advances.

Proinflammatory P2Y14 receptor inhibition protects against ischemic acute kidney injury in mice

Ischemic acute kidney injury (AKI), a complication that frequently occurs in hospital settings, is often associated with hemodynamic compromise, sepsis, cardiac surgery, or exposure to nephrotoxins. Here, using a murine renal ischemia/reperfusion injury (IRI) model, we show that intercalated cells (ICs) rapidly adopted a proinflammatory phenotype after IRI. Wwe demonstrate that during the early phase of AKI either blockade of the proinflammatory P2Y14 receptor located on the apical membrane of ICs or ablation of the gene encoding the P2Y14 receptor in ICs (a) inhibited IRI-induced increase of chemokine expression in ICs, (b) reduced neutrophil and monocyte renal infiltration, (c) reduced the extent of kidney dysfunction, and (d) attenuated proximal tubule damage. These observations indicate that the P2Y14 receptor participates in the very first inflammatory steps associated with ischemic AKI. In addition, we show that the concentration of the P2Y14 receptor ligand UDP-glucose (UDP-Glc) was higher in urine samples from intensive care unit patients who developed AKI compared with patients without AKI. In particular, we observed a strong correlation between UDP-Glc concentration and the development of AKI in cardiac surgery patients. Our study identifies the UDP-Glc/P2Y14 receptor axis as a potential target for the prevention and/or attenuation of ischemic AKI.

Transplantation-Induced Ischemia-Reperfusion Injury Modulates Antigen Presentation by Donor Renal CD11c+F4/80+ Macrophages through IL-1R8 Regulation

BACKGROUND

In donor kidneys subjected to ischemia-reperfusion injury during kidney transplant, phagocytes coexpressing the F4/80 and CD11c molecules mediate proinflammatory responses and trigger adaptive immunity in transplantation through antigen presentation. After injury, however, resident renal macrophages coexpressing these surface markers acquire a proreparative phenotype, which is pivotal in controlling inflammation and fibrosis. No data are currently available regarding the effects of transplant-induced ischemia-reperfusion injury on the ability of donor-derived resident renal macrophages to act as professional antigen-presenting cells.

METHODS

We evaluated the phenotype and function of intragraft CD11c⁺F4/80⁺ renal macrophages after cold ischemia. We also assessed the modifications of donor renal macrophages after reversible ischemia-reperfusion injury in a mouse model of congeneic renal transplantation. To investigate the role played by IL-1R8, we conducted in vitro and in vivo studies comparing cells and grafts from wild-type and IL-R8-deficient donors.

RESULTS

Cold ischemia and reversible ischemia-reperfusion injury dampened antigen presentation by renal macrophages, skewed their polarization toward the M₂ phenotype, and increased surface expression of IL-1R8, diminishing activation mediated by toll-like receptor 4. Ischemic IL-1R8-deficient donor renal macrophages acquired an M₁ phenotype, effectively induced IFNγ and IL-17 responses, and failed to orchestrate tissue repair, resulting in severe graft fibrosis and aberrant humoral immune responses.

CONCLUSIONS

IL-1R8 is a key regulator of donor renal macrophage functions after ischemia-reperfusion injury, crucial to guiding the phenotype and antigen-presenting role of these cells. It may therefore represent an intriguing pathway to explore with respect to modulating responses against autoantigens and alloantigens after kidney transplant.

CD4+ T Cell-Derived NGAL Modifies the Outcome of Ischemic Acute Kidney Injury

CD4⁺ T cells mediate the pathogenesis of ischemic and nephrotoxic acute kidney injury (AKI). However, the underlying mechanisms of CD4⁺ T cell-mediated pathogenesis are largely unknown. We therefore conducted unbiased RNA-sequencing to discover novel mechanistic pathways of kidney CD4⁺ T cells after ischemia compared with normal mouse kidney. Unexpectedly, the lipocalin-2 (Lcn2) gene, which encodes neutrophil gelatinase-associated lipocalin (NGAL) had the highest fold increase (∼60). The NGAL increase in CD4⁺ T cells during AKI was confirmed at the mRNA level with quantitative real-time PCR and at the protein level with ELISA. NGAL is a potential biomarker for the early detection of AKI and has multiple potential biological functions. However, the role of NGAL produced by CD4⁺ T cells is not known. We found that ischemic AKI in NGAL knockout (KO) mice had worse renal outcomes compared with wild-type (WT) mice. Adoptive transfer of NGAL-deficient CD4⁺ T cells from NGAL KO mice into CD4 KO or WT mice led to worse renal function than transfer of WT CD4⁺ T cells. In vitro-simulated ischemia/reperfusion showed that NGAL-deficient CD4⁺ T cells express higher levels of IFN-γ mRNA compared with WT CD4⁺ T cells. In vitro differentiation of naive CD4⁺ T cells to Th17, Th1, and Th2 cells led to significant increase in Lcn2 expression. Human kidney CD4⁺ T cell NGAL also increased significantly after ischemia. These results demonstrate an important role for CD4⁺ T cell NGAL as a mechanism by which CD4⁺ T cells mediate AKI and extend the importance of NGAL in AKI beyond diagnostics.

Bone marrow-derived Ly6C- macrophages promote ischemia-induced chronic kidney disease

Macrophages play an important role in renal injury and repair after acute kidney injury (AKI) and the subsequent chronic kidney disease (CKD) that often results. However, as macrophages have a high degree of plasticity and heterogeneity, the function(s) of macrophage subtypes in AKI-to-CKD progression are not fully understood. Here, we focused on Ly6C⁻ macrophages, which are derived from the embryonic yolk sac and post-development become resident in the kidneys. We found that C–C chemokine receptor type 2 (CCR2) deficiency, which blocks the migration of Ly6C⁺ macrophages from the bone marrow to the sites of injury, alleviated ischemia-induced AKI in mice. Unexpectedly, though, CCR2 deficiency worsened the subsequent renal fibrosis, which was marked by notable intra-renal infiltration of Ly6C⁻ macrophages. These Ly6C⁻ macrophages were greater in number in both the acute and chronic phases after ischemia reperfusion (I/R) in kidneys of wild type (WT) mice, and we showed them to be derived from the bone marrow by bone marrow chimerism. Clodronate Liposomes (CLs)-mediated depletion of renal Ly6C⁻ macrophages in CCR2^−/− mice or in WT mice after I/R alleviated the renal injury and fibrosis. On the contrary, adoptive transfer of Ly6C⁻ macrophages from injured kidneys of WT mice into immune-deficient mice was sufficient to induce renal injury and fibrosis. Transcriptome sequencing of Ly6C⁻ macrophages from injured kidneys revealed that they secreted various cytokines and growth factors, which were associated with the transdifferentiation of fibroblasts into myofibroblasts. This transdifferentiation effect was further supported by in vitro studies showing that Ly6C⁻ macrophages induced the secretion of extracellular matrix proteins from co-cultured fibroblasts. In conclusion, the presence of bone marrow-derived Ly6C⁻ macrophages after ischemia induces AKI and worsens subsequent CKD.

Granulocyte macrophage-colony stimulating factor: A key modulator of renal mononuclear phagocyte plasticity

Macrophage-colony stimulating factor (M-CSF) and granulocyte macrophage-colony stimulating factor (GM-CSF) play key roles in the differentiation of macrophages and dendritic cells (DCs). We examined the effect of treatment with M-CSF-containing macrophage medium or GM-CSF-containing DC medium upon the phenotype of murine bone marrow-derived macrophages and DCs. Culture of macrophages for 5 days in DC medium reduced F4/80 expression and increased CD11c expression with cells effectively stimulating T cell proliferation in a mixed lymphocyte reaction. DC medium treatment of macrophages significantly reduced phagocytosis of both apoptotic cells and latex beads and strongly induced the expression of the chemokine receptor CCR7 known to be involved in DC trafficking to lymph nodes. Lysates of obstructed murine kidneys expressed both M-CSF and GM-CSF though M-CSF expression was dominant (M-CSF:GM-CSF ratio ∼30:1). However, combination treatment with both M-CSF and GM-CSF (ratio 30:1) indicated that small amounts of GM-CSF skewed macrophages towards a DC-like phenotype. To determine whether macrophage phenotype might be modulated in vivo we tracked CD45.1⁺ bone marrow-derived macrophages intravenously administered to CD45.2⁺ mice with unilateral ureteric obstruction. Flow cytometry of enzyme dissociated kidneys harvested 3 days later indicated CD11c and MHC Class II upregulation by adoptively transferred CD45.1⁺ cells with CD45.1⁺ cells evident in draining renal lymph nodes. Our data suggests that GM-CSF modulates mononuclear phagocyte plasticity, which likely promotes resolution of injury and healing in the injured kidney.

Kidney-resident macrophages promote a proangiogenic environment in the normal and chronically ischemic mouse kidney

Renal artery stenosis (RAS) caused by narrowing of arteries is characterized by microvascular damage. Macrophages are implicated in repair and injury, but the specific populations responsible for these divergent roles have not been identified. Here, we characterized murine kidney F4/80+CD64+ macrophages in three transcriptionally unique populations. Using fate-mapping and parabiosis studies, we demonstrate that CD11b/cint are long-lived kidney-resident (KRM) while CD11chiMϕ, CD11cloMϕ are monocyte-derived macrophages. In a murine model of RAS, KRM self-renewed, while CD11chiMϕ and CD11cloMϕ increased significantly, which was associated with loss of peritubular capillaries. Replacing the native KRM with monocyte-derived KRM using liposomal clodronate and bone marrow transplantation followed by RAS, amplified loss of peritubular capillaries. To further elucidate the nature of interactions between KRM and peritubular endothelial cells, we performed RNA-sequencing on flow-sorted macrophages from Sham and RAS kidneys. KRM showed a prominent activation pattern in RAS with significant enrichment in reparative pathways, like angiogenesis and wound healing. In culture, KRM increased proliferation of renal peritubular endothelial cells implying direct pro-angiogenic properties. Human homologs of KRM identified as CD11bintCD11cintCD68+ increased in post-stenotic kidney biopsies from RAS patients compared to healthy human kidneys, and inversely correlated to kidney function. Thus, KRM may play protective roles in stenotic kidney injury through expansion and upregulation of pro-angiogenic pathways.

Correction: Characterization of kidney CD45intCD11bintF4/80+MHCII+CX3CR1+Ly6C- "intermediate mononuclear phagocytic cells"

[This corrects the article DOI: 10.1371/journal.pone.0198608.].