We have used the unlabeled antibody, peroxidase-antiperoxidase (PAP) method of Sternberger, 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. It is shown that trypsin digestion prior to the PAP technique can reveal glomerular, vascular, and tubular deposits of immunoglobulins IgG, IgA, IgM, and IgD and complement components C3, C4, and C1q in routinely fixed and processed needle biopsy specimens of the kidney. Solutions of 0.05% trypsin have been found to work most satisfactorily. With insufficient treatment, there is no immunochemical reaction, whereas excessive incubation produces loss of complement components C3 and C4, an increase in staining of connective tissue, and eventual disintegration of the section. The results of this method and those of conventional immunofluorescence performed on frozen renal tissue show good correlation. The use of the technique in retrospective studies has been demonstrated.
