[Immunohistochemical analysis of the normal and cystic kidney using antibody against polycystin 2]

A second gene responsible for polycystic kidney disease(PKD) has been identified recently, and an antisera(YCC2) against this gene's product, polycystin 2, has been generated. In the present study, we investigated the normal distribution of polycystin 2 in human adult kidneys and analyzed the expression of polycystin 2 in the cystic tubules of kidneys from patients with PKD and acquired cystic disease of the kidney(ACDK). The expression of polycystin 2 in normal regions of resected human kidneys, 4 cases of autosomal dominant polycystic kidney disease(ADPKD) and 4 cases of ACDK was examined by immunohistochemically staining the specimens with a polyclonal antibody specific to the C-terminal region of polycystin 2. This region is specific to polycystin 2 and does not crossreact with polycystin 1. In normal kidneys, prominent expression of polycystin 2 was observed in the distal tubules. A faint level of expression was detected in the proximal tubules, and the glomerulus and vessels were almost negative for expression. In the cystic kidneys of ADPKD patients, 68.7% of the cystic tubules stained positively for YCC2, although partial staining was seen in 41.2% of the positive cystic tubules. Although the genetic background of the samples is unknown, the co-existence of positive and negative cysts suggest that a "two-hit" hypothesis is feasible and that the mutations are likely to be missense or in frame changes. In ACDK cysts, YCC2-positive staining was prominent in small cysts (less than 0.5 mm in diameter), which were also positive for DBA, a marker for distal tubules. In contrast, larger cysts of more than 0.5 mm in diameter which stained positive for a proximal tubule marker, Lotus T, tended to be less positively stained for YCC2. Overall, 94.5% of the cysts stained positive for YCC2, which is a much higher rate than that of PKD cysts. These results suggest that ACDK cysts may be generated by a different mechanism from that of PKD cysts.