Objective: To assess the nature, distribution and expression pattern of CD75, a neuraminidase-sensitive lymphocyte cell surface differentiation antigen, in calcium oxalate (CaOx) stone disease, as cell-surface sialic acid might be involved CaOx crystal binding, and lectin-binding assays suggest that sialic acid in the alpha2,6 position is upregulated in stone-forming kidneys.
Materials and methods: Human CaOx stone-forming and normal kidneys (13 each) and primary kidney epithelial cells (CAKI-1, three samples) were analysed. The protein pattern, distribution and expression of CD75 were analysed using Western blotting, immunohistology and semi-quantitative confocal laser scanning microscopy (cLSM). Production was investigated by alpha2,6-sialyltransferase specific reverse transcription-polymerase chain reaction.
Results: Western blotting showed one strong band at approximately 43 kDa that reacted with anti-CD75 when renal epithelial and CAKI-1 tumour cell extracts were analysed. However, in renal tissue extracts of CaOx stone formers there were additional bands at 120 and 205 kDa. Image processing after cLSM showed that anti-CD75 reactivity was significantly greater on E-cadherin-positive distal and collecting tubular cells from CaOx stone-forming kidneys, at a mean (sd) intensity of 87 (7), than on those from normal kidneys, at 41 (5) (P = 0.005).
Conclusion: CD75 expression in human kidney was primarily on the luminal surface of distal tubules and collecting ducts. Whether increased epithelial CD75 expression in CaOx stone disease is a cause or result of the disease remains to be clarified.