IMMUNOSTAINING OF CARDIAC BIOPSY SPECIMENS IN THE DIAGNOSIS OF ACUTE VASCULAR (HUMORAL) REJECTION - A CONTROL STUDY

The diagnosis of acute vascular (humoral) rejection in heart transplan t biopsies is classically based on immunofluorescent studies of frozen tissue that show vascular staining for immunoglobulin and complement. We have noted that some pathologists have used immunostaining of form alin-fixed, paraffin-embedded tissue in testing for vascular rejection . To determine the specificity of immunostaining of heart biopsy speci mens in the diagnosis of vascular rejection, we studied tissue from 68 consecutive endomyocardial biopsies from 16 patients without clinical or histologic evidence of vascular rejection. In each case, routinely processed formalin-fixed, paraffin-embedded tissue was stained for im munoglobulin G and immunoglobulin M with an avidin-biotin immunoperoxi dase technique. Frozen tissue from each case was also stained for immu noglobulin G, immunoglobulin M, C3, and Clq by immunofluorescence. Imm unoperoxidase stains on formalin-fixed tissue showed vascular staining for immunoglobulin in 67 of 68 (99%) of the cases. Staining was ablat ed if the antibodies were absorbed with their appropriate immunoglobul in. Immunofluorescent studies on frozen tissue showed no vascular stai ning for immunoglobulin or complement. We conclude that immunoperoxida se studies of routinely processed, formalin-fixed, paraffin-embedded t issues are nonspecific in the diagnosis of heart acute vascular reject ion. The positive staining in fixed tissues may be due to labeling of passive immunoglobulins that are ''fixed'' in the vessels during routi ne processing but are washed away in techniques using frozen tissue.