Immunoenzymatic Staining of Caveolin-1 in Formalin-Fixed Renal Graft Showing Chronic Antibody Mediated Rejection

Caveolin-1 (CAV-1) is a molecule associated with endothelial cell dysfunction in chronic antibody-mediated rejection (CAMR) and considered to be a novel biomarker of CAMR. For immunohistochemical staining to reveal CAV-1 expression, most studies have used immunofluorescent stained frozen specimens, whereas formalin-fixed tissues have not been utilized. In the present study, we examined CAV-1 expression in specimens from CAMR patients using an immunoenzymatic technique with formalin-fixed tissues.

Eleven patients diagnosed with CAMR based on findings of transplanted renal biopsy samples were enrolled. Those biopsy specimens were formalin fixed and stained with CAV-1 using an immunoenzymatic method. Dye extent was evaluated by classifying that in peritubular capillaries (PTC) and glomerular capillaries (GBM) in 3 steps. We then compared the Banff scores for peritubular capillaritis (ptc), glomerulopathy (cg), and C4d using those results.

CAV-1 expression was confirmed in vascular endothelium (PTC, GBM), while it was poor in epithelial cells. A Banff score for ptc and cg of 3 points was seen in 3 and 4 cases, of 2 points was seen in 1 and 4 cases, of 1 point was seen in 7 and 3 cases, and of 0 points was seen in 0 and 0 cases, respectively. In PTC, C4d and CAV-1 scores of 3 points were seen in 0 and 9 cases, of 2 points were seen in 2 and 2 cases, of 1 point was seen in 5 and 0 cases, and of 0 points were seen in 4 and 0 cases, respectively. As for GBM, C4d and CAV-1 scores of 3 points were seen in 8 and 7 cases, of 2 points were seen in 2 and 4 cases, of 1 point was seen in 0 and 0 cases, and of 0 points were seen 1 and 0 cases, respectively.

CAV-1 expression in PTC had a score ≥2 in all cases, indicating that an adequate level of staining of formalin-fixed tissue was attained with the present immunoenzymatic technique. These results suggest that CAV-1 expression examined by the present method may be useful for identifying endothelial dysfunction.