DR Expression on Vascular Endothelial Cells in Normal Human Kidney

P. Arrizabalaga, MD, Servicio de Nefrología, Hospital Clínico, c/Casanova, 143, E-Barcelona 36 (Spain) Dear Sir, Human HLA-DR antigens are expressed on cytoplas-mic membrane of cells associated with immunological activity [1]. Moreover, the HLA-DR expression can be induced on other cells which are normally negative for HLA-DR molecules. Thus, the thyroid follicular cells bear these antigens when cultured with mitogens [2]. The umbilical vein endothelial cells express HLA-DR when cultured with phytohemagglutinin [3] or co-cultured with activated T cells [4]. Häyry et al. [5] observed HLA-DR antigens on the dispersed kidney vascular endothelial cells. In addition, morphological studies on tissue sections suggest that renal vascular endothelium appears to express HLA-DR antigens [6–8]. We have observed, using immunofluorescence (IF) microscopy and a nucleic acid counterstain with ethidium bromide (EB), that in the normal human kidney these antigens are localized on the vascular endothelium around cellular structures. We have used a mouse monoclonal antibody directed against a monomorphic determinant of HLA-DR (Edu-1) described elsewhere [9, 10]. Normal renal tissue from 2 biopsy and 9 necropsy specimens was tested for HLA-DR antigens by indirect IF technique. A nucleic acid stain with EB was used for cellular localization. Tonsil sections were used as positive control. Monoclonal antibody to non-HLA-DR antigens (Cris-1) [9,11] and ascitic fluid, obtained intraperitoneally of Balb/c NSA myeloma line were used as negative controls. A constant pattern of HLA-DR antigens was observed in all the specimens. Heavy IF staining was identified in the renal interstitium and in the glomerular capillary walls. Moreover, bright staining was observed in the mesan-gium. EB counterstaining showed HLA-DR antigens around endothelial cells in glomerular capillaries (fig. la) and probably vascular endothelial cells in intertubular capillaries (fig. lb). The considerable amount of HLA-DR antigens observed in capillaries of human normal kidney suggest at least two biological implications. First, the vulnerability of the microcirculation of transplanted kidney to circulating antibodies with specificity for HLA-DR antigens