Cx3cr1 controls kidney resident macrophage heterogeneity

Recruitment of pulmonary intravascular macrophages in SARS-CoV-2 infected hamsters

The mechanisms by which severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes severe lung inflammation and mortality remain unclear. While the role of alveolar macrophages in COVID-19 is known, data on pulmonary intravascular macrophages (PIMs) is lacking. PIMs are key inflammatory cells present in species like cattle and pigs. Though constitutively absent in humans and rodents, their recruitment in rodents triggers exaggerated inflammation. We investigated the recruitment of PIMs and other immune cells, using immunofluorescence, hematoxylin and eosin (H&E) staining, and immunogold labeling in a hamster model of SARS-CoV-2 infection. Syrian golden hamsters were divided into 6 groups: uninfected control, unvaccinated-infected at 2-, 5-, and 14-days post infection (dpi) and vaccinated-infected at 5- and 14-dpi. Lung tissues were analyzed for neutrophils (myeloperoxidase), monocytes/macrophages (CCR2, CX3CR1), macrophages (IBA-1), and T cells (CD3). Septal macrophages increased at 2-, 5-, and 14-dpi in infected animals vs. control. CX3CR1 + cells decreased at 14-dpi in unvaccinated animals, but CX3CR1/CCR2 double positive cells were higher at 5-dpi, indicating a pro-inflammatory macrophage phenotype. PIMs were confirmed by transmission electron microscopy. These are the first data showing recruitment of pro-inflammatory PIMs in SARS-CoV-2 infected lungs.

Tissue-resident macrophages and renal diseases: landscapes and treatment directions

Tissue-resident macrophage (TRM) is a specialized subset of macrophage that resides within specific tissues and organs. TRMs play crucial roles in resisting pathogen invasion, maintaining the homeostasis of the immune microenvironment, and promoting tissue repair and regeneration. The development and function of TRMs exhibit significant heterogeneity across different tissues. Kidney TRMs (KTRMs) originate from both embryonic yolk sac erythro-myeloid progenitors and the fetal liver, demonstrating the capacity for self-renewal independent of bone marrow hematopoiesis. KTRMs are not only essential for the maintenance of renal homeostasis and the monitoring of microvascular environment, but contribute to renal injury due to inflammation, fibrosis and immune dysfunction in kidneys. In this review, we summarize currently available studies on the regulatory role of KTRMs in processes of renal injury and repair. The altering effects and underlying mechanisms of KTRMs in regulating local tissue cells and immune cells in different renal diseases are reviewed, primarily including lupus nephritis, diabetic nephropathy, renal fibrosis, and renal carcinoma. Understanding the plasticity and immune regulatory functions of KTRMs may offer new insights into the pathogenesis and the exploration of therapeutic strategies of kidney diseases.

The association between fractalkine/CX3CR1 axis with IgA vasculitis and nephritis

BACKGROUND

The study investigated whether the fractalkine/CX3CR1 axis is associated with the presence and severity of IgA vasculitis (IgAV) and IgA vasculitis nephritis (IgAVN) in children.

METHODS

We included 59 children with IgAV, 42 children with IgAVN (including 18 children with kidney biopsy), 26 plasma controls and 8 kidney controls. Clinical pathological data were collected, and the fractalkine/CX3CR1 axis and macrophage expression in the circulation and kidneys were detected.

RESULTS

Circulating fractalkine/CX3CR1 axis expression was significantly upregulated in children with IgAV and IgAVN compared to healthy controls. Plasma fractalkine levels and the proportion of CX3CR1+ monocytes were significantly higher in children with IgAVN than in those with IgAV, and the kidney expression of fractalkine/CX3CR1 axis and CD68 were significantly increased in the IgAVN group relative to normal controls, especially in children with IgAVN with more severe ISKDC pathological grading. Additionally, kidney levels of fractalkine, CX3CR1, and CD68 exhibited significant positive correlations with tubulointerstitial grading and serum creatinine levels.

CONCLUSION

The expression of fractalkine/CX3CR1 axis is associated with the presence and severity of IgAV and IgAVN. Our findings support further investigation of fractalkine/CX3CR1 as a target for future therapies in IgAV and IgAN.

IMPACT

The expression of plasma fractalkine/CX3CR1 axis is associated with the presence and severity of IgAV and IgAVN. The expression of kidney fractalkine/CX3CR1 axis and macrophage are upregulated in IgAVN, which is closely associated with poorer kidney function and more severe kidney pathology. Our findings support further investigation of fractalkine/CX3CR1 as a target for future therapies in IgAV and IgAVN.

Progesterone promotes CXCl2-dependent vaginal neutrophil killing by activating cervical resident macrophage-neutrophil crosstalk

Vaginal infections in women of reproductive age represent a clinical dilemma with significant socioeconomic implications. The current understanding of mucosal immunity failure during early pathogenic invasions that allows the pathogen to grow and thrive is far from complete. Neutrophils infiltrate most tissues following circadian patterns as part of normal repair, regulation of microbiota, or immune surveillance and become more numerous after infection. Neutrophils are responsible for maintaining vaginal immunity. Specific to the vagina, neutrophils continuously infiltrate at high levels, although during ovulation, they retreat to avoid sperm damage and permit reproduction. Here we show that, after ovulation, progesterone promotes resident vaginal macrophage-neutrophil crosstalk by upregulating Yolk sac early fetal organs (FOLR2+) macrophage CXCl2 expression, in a TNFA-patrolling monocyte-derived macrophage-mediated (CX3CR1hiMHCIIhi-mediated) manner, to activate the neutrophils' capacity to eliminate sex-transmitted and opportunistic microorganisms. Indeed, progesterone plays an essential role in conciliating the balance between the commensal microbiota, sperm, and the threat of pathogens because progesterone not only promotes a flurry of neutrophils but also increases neutrophilic fury to restore immunity after ovulation to thwart pathogenic invasion after intercourse. Therefore, modest progesterone dysregulations could lead to a suboptimal neutrophilic response, resulting in insufficient mucosal defense and recurrent unresolved infections.

Kidney resident macrophages have distinct subsets and multifunctional roles

BACKGROUND

The kidney contains distinct glomerular and tubulointerstitial compartments with diverse cell types and extracellular matrix components. The role of immune cells in glomerular environment is crucial for dampening inflammation and maintaining homeostasis. Macrophages are innate immune cells that are influenced by their tissue microenvironment. However, the multifunctional role of kidney macrophages remains unclear.

METHODS

Flow and imaging cytometry were used to determine the relative expression of CD81 and CX3CR1 (C-X3-C motif chemokine receptor 1) in kidney macrophages. Monocyte replenishment was assessed in Cx3cr1CreER X R26-yfp-reporter and shielded chimeric mice. Bulk RNA-sequencing and mass spectrometry-based proteomics were performed on isolated kidney macrophages from wild type and Col4a5-/- (Alport) mice. RNAscope was used to visualize transcripts and macrophage purity in bulk RNA assessed by CIBERSORTx analyses.

RESULTS

In wild type mice we identified three distinct kidney macrophage subsets using CD81 and CX3CR1 and these subsets showed dependence on monocyte replenishment. In addition to their immune function, bulk RNA-sequencing of macrophages showed enrichment of biological processes associated with extracellular matrix. Proteomics identified collagen IV and laminins in kidney macrophages from wild type mice whilst other extracellular matrix proteins including cathepsins, ANXA2 and LAMP2 were enriched in Col4a5-/- (Alport) mice. A subset of kidney macrophages co-expressed matrix and macrophage transcripts.

CONCLUSIONS

We identified CD81 and CX3CR1 positive kidney macrophage subsets with distinct dependence for monocyte replenishment. Multiomic analysis demonstrated that these cells have diverse functions that underscore the importance of macrophages in kidney health and disease.

Renal macrophages monitor and remove particles from urine to prevent tubule obstruction

When the filtrate of the glomerulus flows through the renal tubular system, various microscopic sediment particles, including mineral crystals, are generated. Dislodging these particles is critical to ensuring the free flow of filtrate, whereas failure to remove them will result in kidney stone formation and obstruction. However, the underlying mechanism for the clearance is unclear. Here, using high-resolution microscopy, we found that the juxtatubular macrophages in the renal medulla constitutively formed transepithelial protrusions and "sampled" urine contents. They efficiently sequestered and phagocytosed intraluminal sediment particles and occasionally transmigrated to the tubule lumen to escort the excretion of urine particles. Mice with decreased renal macrophage numbers were prone to developing various intratubular sediments, including kidney stones. Mechanistically, the transepithelial behaviors of medulla macrophages required integrin β1-mediated ligation to the tubular epithelium. These findings indicate that medulla macrophages sample urine content and remove intratubular particles to keep the tubular system unobstructed.

Macrophage Depletion Protects Against Cisplatin-Induced Ototoxicity and Nephrotoxicity

Cisplatin is a widely used and highly effective anti-cancer drug with significant side effects including ototoxicity and nephrotoxicity. Macrophages, the major resident immune cells in the cochlea and kidney, are important drivers of both inflammatory and tissue repair responses. To investigate the roles of macrophages in cisplatin-induced ototoxicity and nephrotoxicity, we used PLX3397, an FDA-approved inhibitor of the colony-stimulating factor 1 receptor (CSF1R), to eliminate tissue-resident macrophages during the course of cisplatin administration. Mice treated with cisplatin alone (cisplatin/vehicle) had significant hearing loss (ototoxicity) as well as kidney injury (nephrotoxicity). Macrophage ablation using PLX3397 resulted in significantly reduced hearing loss measured by auditory brainstem responses (ABR) and distortion-product otoacoustic emissions (DPOAE). Sensory hair cells in the cochlea were protected against cisplatin-induced death in mice treated with PLX3397. Macrophage ablation also protected against cisplatin-induced nephrotoxicity, as evidenced by markedly reduced tubular injury and fibrosis as well as reduced plasma blood urea nitrogen (BUN) and neutrophil gelatinase-associated lipocalin (NGAL) levels. Mechanistically, our data suggest that the protective effect of macrophage ablation against cisplatin-induced ototoxicity and nephrotoxicity is mediated by reduced platinum accumulation in both the inner ear and the kidney. Together our data indicate that ablation of tissue-resident macrophages represents a novel strategy for mitigating cisplatin-induced ototoxicity and nephrotoxicity.