Kidney resident macrophages in the rat have minimal turnover and replacement by blood monocytes

Kidney resident macrophages (KRM) are involved in maintaining renal homeostasis and in controlling the pathological outcome of acute kidney injury and cystic kidney disease in mice. In adult mice, KRM maintain their population through self-renewal with little or no input from the peripheral blood. Despite recent data suggesting that a transcriptionally similar population of KRM-like cells is present across species, the idea that they are self-renewing and independent of peripheral blood input in other species has yet to be proven due to the lack of an appropriate model and cross-species expression markers. In this study, we use our recently identified cross-species KRM cell surface markers and parabiosis surgery in inbred Lewis rats to determine if rat KRM are maintained independent of peripheral blood input, similar to their mouse counterparts. Flow cytometry analysis indicates that parabiosis surgery in the rat results in establishment of chimerism of T/B cells, neutrophils, and monocyte-derived infiltrating macrophages in the blood, spleen, and kidney three weeks post parabiosis surgery. Analysis of KRM using the cell surface markers CD81 or C1q indicates that these cells have minimal chimerism and, therefore, receive little input from the peripheral blood. Thus, a putative KRM population in the rat identified using two novel cross-species markers is maintained with minimal input from the peripheral blood confirming that KRM properties are conserved in at least two different species.