Enhancement of fluorescent antibody staining of viral antigens in formalin-fixed tissues by trypsin digestion.

The staining of viral antigens present in formalin-fixed, paraffin-embedded tissues by fluorescent antibodies is markedly enhanced by trypsin digestion. When the trypsin digestion method was used to detect viral antigens present in hamster brain following experimental infection with measles virus, the results were comparable to those obtained with acetone-fixed, freshly frozen tissues that had been sectioned with a cryostat. Measles antigens were readily identified in brain cells from a patient with subacute sclerosing panencephalitis and in lung and liver tissue from a patient with acute giant cell pneumonia, following preparation of the tissues for routine histologic examination. Viral antigens were detected in brain tissue that had been taken from patients with herpes simplex encephalitis and stored in paraffin for up to 15 years. Cells containing antigen could be precisely identified without loss of histologic detail by restaining the same tissue sections with hematoxylin and eosin.