Abstract
Kidney immune cells play important roles in pathogenesis of many diseases, including ischemia-reperfusion injury (IRI) and transplant rejection. While studying murine kidney T cells, we serendipitously identified a kidney mononuclear phagocytic cell (MPC) subset characterized by intermediate surface expression of CD45 and CD11b. These CD45intCD11bint MPCs were further identified as F4/80+MHCII+CX3CR1+Ly6C- cells, comprising ~17% of total CD45+ cells in normal mouse kidney (P < 0.01) and virtually absent from all other organs examined except the heart. Systemic clodronate treatment had more significant depletive effect on the CD45intCD11bint population (77.3%±5.9%, P = 0.03) than on CD45highCD11b+ population (14.8%±16.6%, P = 0.49). In addition, CD45intCD11bint MPCs had higher phagocytic function in the normal kidney (35.6%±3.3% vs. 24.1%±2.2%, P = 0.04), but lower phagocytic capacity in post-ischemic kidney (54.9%±1.0% vs. 67.8%±1.9%, P < 0.01) compared to the CD45highCD11b+ population. Moreover, the CD45intCD11bint population had higher intracellular production of the pro-inflammatory tumor necrosis factor (TNF)-α (58.4%±5.2% vs. 27.3%±0.9%, P < 0.001) after lipopolysaccharide (LPS) stimulation and lower production of the anti-inflammatory interleukin (IL)-10 (7.2%±1.3% vs. 14.9%±2.2%, P = 0.02) following kidney IRI, suggesting a functional role under inflammatory conditions. The CD45intCD11bint cells increased early after IRI, and then abruptly decreased 48h later, whereas CD45highCD11b+ cells steadily increased after IRI before declining at 72h (P = 0.03). We also identified the CD45intCD11bint MPC subtype in human kidney. We conclude that CD45intCD11bint F4/80+MHCII+CX3CR1+Ly6C-population represent a unique subset of MPCs found in both mouse and human kidneys. Future studies will further characterize their role in kidney health and disease.
Highlights
Both innate and adaptive immune mechanisms are important mediators of kidney injury and repair, and several different types of immune cells participate in these processes [1,2,3]
Our results show that CD45intCD11bint mononuclear phagocytic cell (MPC) produced less IL-10 than CD45highCD11b+ cells in response to LPS, but the difference was not statistically significant (7.3%±2.2% vs. 14.2%±3.8%, P = 0.16)
We uncovered the presence of a CD45intCD11bint “intermediate MPCs” population in both murine and human kidneys
Summary
Both innate and adaptive immune mechanisms are important mediators of kidney injury and repair, and several different types of immune cells participate in these processes [1,2,3]. We identified this population as a discrete renal MPCs that is absent in other organs except the heart and had unique phenotypic characteristics and functional properties, including cytokine production profiles and response to systemic clodronate treatment as well as to ischemia-reperfusion injury (IRI). We identified this MPC population in “normal” human kidney samples from patients undergoing nephrectomies for renal cell carcinoma (RCC), extending the relevance of our mouse findings to humans
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