Renal macrophages (RMs) are essential immune cells that maintain kidney homeostasis, regulate immune responses, and promote tissue repair following injury. They perform a variety of functions, including phagocytosis, antigen presentation, and the orchestration of both inflammatory and anti-inflammatory responses1,2,3. Depending on the local environment, RMs can polarize into either pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, either exacerbating injury or facilitating healing4,5,6. Dysregulation of RMs has been implicated in the onset and progression of acute kidney injury (AKI) and chronic kidney disease (CKD), making them critical players in kidney health and pathology7,8. RMs arise from various sources, including yolk sac-derived macrophages during embryogenesis, fetal liver monocytes, and bone marrow-derived monocytes in adulthood. RMs expand and mature in parallel with renal growth postnatally, primarily originating from fetal liver monocytes before birth, with self-maintenance through adulthood supplemented by peripheral monocytes9. In adults, circulating monocytes are recruited to the kidney by homeostatic or injury signals, differentiating into macrophages under local microenvironmental influences. RM maintenance is sustained through local proliferation and periodic replenishment from circulating monocytes9,10,11,12.
We previously demonstrated the use of the human CD59 (hCD59)/intermedilysin (ILY) cell ablation system as a tool13,14 to investigate the distinct fates, dynamics, and microenvironmental niches of RMs derived from either bone marrow or embryonic origins9. ILY selectively lyses human cells within seconds by forming pores in targeted cell membranes15. This specificity arises from ILY's exclusive binding affinity for human CD59 (hCD59), with no interaction or lytic effect on cells from other species lacking this receptor15. Based on this concept, we engineered a tool allowing the rapid, conditional, and targeted ablation of human CD59-expressing cells in transgenic mouse models through the application of intermedilysin (ILY)14. To facilitate the use of this tool, we developed a model of conditional and targeted cell ablation by generating floxed STOP-CD59 knockin mice (ihCD59), in which expression of human CD59 only occurs after Cre-mediated recombination13. Previously, it was found the CX3CR1cre-EFP gene exclusively expressed on CD11bintF480hi, defined as renal macrophages9. Therefore, we used CX3CR1CreER2+/+lines to cross with ihCD59 mice to express hCD59 on renal macrophages. We successfully generated compound mice with the genotype ihCD59+/-/CX3CR1CreER+/-9 (+/-, +/+ and -/- indicate the homozygote, hemizygote, and noncarrier transgenic mice, respectively). Tamoxifen administration in ihCD59+/-/CX3CR1CreER+/- compound mice conditionally labeled and marked RMs by hCD59 expression9. Following the depletion of the RM niche through ILY treatment, peripheral monocytes promptly differentiated into bone marrow-derived RMs, effectively repopulating the niche as previously described in9. This regeneration was critically dependent on the CX3CR1/CX3CL1 signaling axis, underscoring its essential role in both the maintenance and restoration of the RM population9. We also show that due to their distinct glycolytic capacities, embryonic-origin RMs have a higher capacity for scavenging immune complexes and are more sensitive to immune challenges than bone marrow-derived RMs9.
We present a detailed protocol for the selective ablation of RMs to investigate their regeneration using Cre-inducible hCD59 (ihCD59)-mediated rapid cell ablation following administration of ILY. Injection of ILY caused the targeted ablation of RMs that conditionally and specifically express hCD59 in CX3CR1CreER+/-/ihCD59+/- compound mice. After ablation, we monitored macrophage dynamic changes using flow cytometry and found rapid depletion of macrophages followed by the regeneration of RMs. Recombinant ILY was expressed in E. coli BL21(DE3) cells and purified using nickel-NTA affinity chromatography. The purity and functionality of the recombinant ILY were confirmed by SDS-PAGE, spectrophotometry, and a hemolysis assay, demonstrating its characteristic cholesterol-dependent cytolysin activity. We used ILY to deplete the RMs in the mice, achieving efficient macrophage ablation within 1 day of ILY administration. Renal macrophage regeneration began on day 3 post-ablation, with ~85% recovery by day 7. The data suggest that regeneration is primarily driven by monocyte recruitment. This model offers a powerful tool for studying macrophage biology and has therapeutic potential for the targeted manipulation of macrophage populations in kidney diseases. The ihCD59/ILY cell ablation tool can be used to study cell function and regeneration in the kidney, liver, fatty tissue, and other organs.