Immunohistochemistry
When actinomycotic clumps were found in the tonsillar crypts in the HE specimens, the serial sections were immunostained using rabbit hyperimmune serum against A denticolens (DMS 20671). The immunohistochemistry was carried out using the same streptavidin-biotin-peroxidase conjugate (SAB) method as previously described (Murakami and others 1998). Sections of porcine lung without any lesions, which received a direct injection of A denticolens (DMS 20671), were used as positive controls. A section without the primary antiserum was used as a negative control.
As A bovis (Kimball and Frank 1945) and A viscosus (Specht and others 1991) have been reported as causative agents of actinomycosis in horses, they were used to examine the immunohistochemical cross-reactions between A denticolens and two species of the genus Actinomyces. The strains used for this analysis were A denticolens (DMS 20671), A bovis (ATCC 13683) and A viscosus (ATCC15987). The preparation of these tissue samples has already been described (Murakami and others 1998).