Immunohistochemical detection of feline calicivirus in formalin-fixed, paraffin-embedded specimens.

An immunohistochemical technique was developed for detection of feline calicivirus (FCV) in formalin-fixed, paraffin-embedded cultured cells and tissues. Initial trials with cultured cells indicated that the indirect immunoperoxidase method using rabbit antiserum to FCV strain 255, and horseradish peroxidase-labelled antibodies to rabbit immunoglobulin G lacked sensitivity and showed excessive diffuse background staining despite trypsin digestion of sections before staining. An amplified indirect immunoperoxidase technique using commercially available biotinylated antirabbit antibodies and avidin-biotin-peroxidase or streptavidin-peroxidase (SP) complexes proved highly successful. When optimal conditions, including those for trypsinization, inactivation of endogenous peroxidase and blocking were determined, the SP technique was preferred. Applied to tissue of cats in the acute phase of FCV infection, the technique provided clear identification of cells containing FCV antigens in sections in which histological detail was well preserved.