Problems of cyclosporine localization in the renal tissue

The aim of the present investigation was to localize cyclosporine (CSA) in the rat kidney. The experimental approaches included autoradiography after i.v. injection of 3H-CSA, immunofluorescence after i.v. injection of fluorochrome labeled CSA and immunohistochemistry using the rabbit-alpha-CSA antibody. It was not possible to localize CSA in specific structures of the rat kidney. Finally, immunohistochemistry of human renal tissue gave only an unspecific staining of proximal tubular cells, which was lost when the antibody was absorbed on renal tissue homogenate. In vitro binding of 3H-CSA on renal homogenate indicated only unspecific absorption of the highly lipophilic compound; no specific binding was detected on cytosolic renal fractions. The failure to demonstrate CSA in tubular or arteriolar lesions might have been due to the fact that the affinity of binding is too low for detection, or that CSA does not accumulate within these structures.