Demonstration of extracellular immunoproteins in formalin-fixed renal biopsy specimens

Immunohistochemical techniques have been used for many years to establish the pathogenesis of renal disease. Deposits of immunoglobulin and complement are present in granules in glomerular capillary walls and mesangium in immune-complex disorders, whereas linear deposits of immunoglobulin and complement are found within the capillary walls in disorders due to antibodies directed against the glomerular basement membrane [1]. The diagnosis and classification of renal disease is often based on the detection of specific immunoglobulin classes and their site of deposition [2]. Either immunofluorescent or immunoperoxidase methods can be applied to renal tissue that has been frozen at the time of biopsy, and the two methods give similar results [3–5]. In almost every case, these methods are unable to demonstrate extracellular deposits of immunoglobulin and complement if the tissue has been fixed in formalin. Following the reports of Huang, Minnasian, and More [6] and of Curran and Gregory [7], we have investigated the use of an immunoperoxidase technique on formalin-fixed wax-embedded needle-biopsy specimens of the kidney after prior treatment with trypsin. We have used the unlabeled antibody, peroxidase-antiper-oxidase (PAP) method of Sternberger [8] and have shown that controlled treatment with trypsin prior to the PAP method enables extracellular deposits of both immunoglobulin and complement to be demonstrated. The results are compared with those obtained from standard immunofluorescent methods performed on renal tissue frozen at the time of biopsy