Monocyte/macrophage derived cells in normal and transplanted human kidneys

The existence of HLA-DR/Ia-like antigen (Ia)-bearing cells of the mononuclear phagocyte system, macrophages (Mac), and/or interdigitating cells (IDC), in the normal kidney is controversial. If present, such cells may be important in renal transplant rejection. We performed enzyme histochemistry using alpha-naphthyl acetate/butyrate esterases (alpha NAE, alpha NBE), 5'-nucleotidase (5'N), acid phosphatase (AcP), alkaline phosphatase (AlkP), and ATPase (ATP) as well as immunoperoxidase staining for Ia and lectin binding (Ulex europaeus I; UEA) on plastic-embedded tissue sections of normal kidneys and rejected renal allografts. Plastic embedding provides clear visualization of histologic detail and allows specific identification of immunoperoxidase-stained cells. Mac and IDC (shown to be Ia+, alpha NAE+, AcP+, ATP+ in other sites) could not be demonstrated in normal renal interstitium. IDC and Mac were not generally identified in normal mesangium, although they could not be altogether distinguished from Ia+ endothelial cells. Focal mesangial staining for alpha NAE but not alpha NBE was present. Rejected kidneys showed increased numbers of alpha NAE+ cells in glomeruli. These cells were frequently Ia negative and often appeared to be blood monocytes present in capillary lumens. Peritubular capillaries and glomerular endothelium stained strongly for UEA, 5'N, and Ia. Our results suggest that previous reports of the presence of IDC in renal tissue on the basis of staining for Ia on frozen tissue may be due to staining of compressed or obliquely sectioned vascular structures that were not adequately visualized.