We report the rapid (less than 1 hr), immunocytochemical identification of various fungi in formalin-fixed, paraffin-embedded tissues using antisera originally developed for use in immunodiffusion assays. Primary antisera directed towards fungal genera including Aspergillus, Blastomyces, Candida, Coccidioides, Cryptococcus, Histoplasma, and Sporothrix were examined. The specificity of each antiserum was evaluated by the presence or absence of crossreactivity with other morphologically similar fungi in both paraffin-embedded pure fungal cultures and tissues with culture-confirmed fungal infections. Each antiserum reacted strongly with the fungus to which it had been raised, whether examined in pure culture or infected tissues. The antisera raised against Candida, Cryptococcus, and Sporothrix did not exhibit cross-reactivity with any other fungus tested. However, the antisera raised to Aspergillus, Blastomyces, Coccidioides, and Histoplasma demonstrated significant crossreactivity with other genera of fungi, thus precluding their routine use in diagnostic immunocytochemistry. The results indicate that immunocytochemistry may provide an important adjunct to other methods, such as immunodiffusion or complement fixation assays and histochemical stains such as the Grocott methenamine silver or periodic acid-Schiff, when attempts are made to specifically identify certain fungi in formalin-fixed, paraffin-embedded tissues before mycology culture results are available.
Degradation of fungal DNA in formalin-fixed paraffin-embedded sinus fungal balls hampers reliable sequence-based identification of fungi
