Heterogeneity of HLA-DR+ cells in normal human kidney. Immunohistological and cytochemical characterisation of discrete cell populations.

Biopsies of normal kidneys taken at time of transplantation were studied using a variety of immunofluorescent and cytochemical techniques. A heterogeneous population of HLA-DR+ cells was found, mainly confined to the intertubular interstitium. The majority of these cells (80%) were positive when stained with a rabbit anti-factor VIII antiserum suggesting that they were endothelial cells. A minority however (20%) were factor VIII- but were positively stained with FMC17, a monoclonal antibody (McAb) directed against human monocyte/macrophage antigens. Positive staining of this subpopulation was also noted with RFD1, a McAb which reacts with an antigen on human interdigitating cells (ID cells). Cytochemical reactions revealed that these cells contain adenosine triphosphatase (ATPase) and acid phosphatase (ACP) and thus do not conform to the phenotype of tissue histiocytes. The phenotype of this latter population is identical with that of the ID cells found in tonsil, thymus and spleen and it is suggested that they play a major role in initiating the process of renal allograft rejection.