Reactions to Pythium insidiosum by sera from horses with active
pythiosis were investigated by
sodium dodecyl sulfate-
polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Five strains of P. insidiosum were grown in nutrient broth and then sonicated. After centrifugation, supernatant
antigens were separated by SDS-PAGE. An exoantigen of Conidiobolus coronatus was also tested. Bands with molecular weights between 97,000 and 14,000 were identified by
Coomassie blue and
silver staining. After being transferred to
nitrocellulose, the
antigens were reacted against sera from six horses with
pythiosis, sera from four horses cured a year earlier by vaccination, and sera from five healthy horses. The sera from horses with
pythiosis recognized at least 20
antigens in all strains. Three
antigens with molecular weights of 32,000, 30,000, and 28,000 appeared to be immunodominant and specific. Sera from horses cured by
immunotherapy showed only five very weak bands, three of them the 32,000-molecular-weight (32K), 30K, and 28K
antigens. No bands were observed with sera from healthy horses or sera from horses with a variety of other
infections. Sera from horses with
pythiosis cross-reacted with the 44K
antigen of C. coronatus. The
immunodominant antigens described here may be useful for diagnostic purposes and in
immunotherapy for this oomycotic
infection in horses.