Renal dendritic cells:

The renal tubulointerstitium is populated by numerous bone marrow-derived cells of the immune system that express MHC class II molecules, indicating that they belong to a class of professional antigen-presenting cells (APCs), such as the dendritic cells (DCs) or the macrophages. More than 20 years ago, the tubulointerstitial immunocytes were shown to express the macrophage markers CD11b (Mac-1) and F4/80 (J Exp Med 157:1704-1709, 1983), whereas several studies failed to detect the murine DC marker CD11c, leading to their classification as "resident tissue macrophages".

Generally, classification of cells by immunohistology is convenient, but depends on the specificity and sensitivity of one single marker. Recent studies on APC subpopulations have demonstrated the existence of DC subpopulations expressing CD11b and F4/80, whereas CD11c is still considered to be relatively specific for murine DCs, at least in lymphoid tissues (Nature Rev Immunol 2:151-161, 2002). Using suitable immunohistochemical methods, we have recently shown that CD11c is expressed by renal tubulointerstitial immunocytes, raising doubt on the surface marker-based classification as macrophages. Therefore, we decided to reevaluate the classification of CD11c+ tubulointerstitial immunocytes by examining their functional properties.