Immune Cells in Compensatory Kidney Hypertrophy after Unilateral Nephrectomy

Background: The mechanisms of compensatory renal hypertrophy (CRH) following unilateral nephrectomy (UNx) are incompletely understood. We hypothesized that immune cells are involved in the compensatory increase in kidney size and function. Methods: C57BL/6J mice underwent left kidney UNx. GFR was measured by transdermal FITC-sinistrin clearance. Kidney mononuclear cells were harvested from the remnant kidney and immunophenotyped via flow cytometry. Single-cell RNA sequencing (scRNA-seq) was performed on CD45+ cells post-UNx to capture gene expression changes. Adaptive immunity in CRH was evaluated using Rag1-/- mice lacking T and B cells. Results: Kidney to-body weight ratio (KW:BW) for the remnant kidney increased at 24hr (5.5±0.2 mg/g baseline vs 6.7±0.1 mg/g 24hr; P<0.001) and 8wk (8.1±0.3 mg/g) while GFR fell at 4hr (47.6±6.5% average WT baseline; P<0.001) then rose at 24hr (73.5±4.4% vs 4hr; P<0.01) and stabilized throughout the 8wk period. Flow cytometry showed that, compared to baseline (56.7±2.2% CD4; 31.2±1.9% CD8; 11.8±0.8% CD4-CD8-), CD4 T cells increased at 4hr (67.5%; P<0.01) and 8wk (65.7±1.3%; P<0.05), CD8 T cells decreased at 4hr (15.8±3.5%; P<0.001) and 72hr (13.2±1.5%; P<0.001), and CD4-CD8- double negative T cells rose at 72hr (31.2±2.7%; P<0.001). PD1+CD4 T cells were elevated at 4wk (31.5±2.1%) compared to 1wk (14.8±1.3%; P<0.05) and 8wk (16.0±1.7%; P<0.05). TIGIT+CD8 T cells rose at 4hr compared to baseline (3.2±1.3% vs 1.0±0.2%; P<0.05). scRNA-seq showed changes in B cells (16.7% control, 22.6% 24hr, 16.0% 1wk, 20.5% 4wk), neutrophils (1.5% control, 10.8% 24hr, 5.8% 1wk, 2.6% 4wk), and NK cells (6.5% control, 8.5% 24hr, 12.6% 1wk, 12.9% 4wk). Rag1-/- GFR was increased compared to WT at 4hr (68.9±4.4% average Rag1-/- baseline; P≤0.05), 1wk (90.0±4.3%; P<0.01), and 4wk (93.3±3.9%; P<0.05). KW:BW at 4wk and 8wkwere similar for WT vs Rag1-/-. Conclusion: Immune cells in the remnant kidney quantitatively and phenotypically change after UNx, seen in flow cytometry and scRNAseq. T and B cell deficiency led to increased GFR at select time points after UNx. Immune cells may participate in the compensatory GFR increase after UNx with implications for kidney donors, transplant recipients, recovery from AKI, and CKD progression. Funding: NIDDK Support