Selective assay for CyPA and CyPB in human blood using highly specific anti-peptide antibodies

Cyclophilins A and B (CyPA and CyPB) are known to be the main binding proteins for cyclosporin A (CsA), a potent immunosuppressive drug. Due to the high homology between the two proteins, antibodies to CyPB were found to cross-react with CyPA. In order to avoid this phenomenon, we raised specific antibodies against peptides copying the most divergent parts of the two sequences. These antibodies allowed us to develop an ELISA capture assay selective for either isotype. Thus, we showed that leukocyte CyPB concentration was almost ten times lower than that of CyPA, and that in contrast to the results described in the literature, only CyPB was released in plasma. Moreover, CyPB levels in leukocytes and plasma were found to correlate for the same donor, but no relationship was found with CyPA level.