Monoclonal antibodies to cell surface components of zoospores and cysts of the fungus Pythium aphanidermatum reveal species-specific antigens

Abstract

A panel of monoclonal antibodies (MAbs) designated PA1 to PA8 has been raised against cell surface components of zoospores and cysts of the pathogenic fungus Pythium aphanidermatum. The antibodies were selected on the basis of binding assays using indirect immunofluorescence. Four binding patterns were observed: PA1 labeled the entire zoospore surface including both flagella, PA2 binding was restricted to the anterior flagellum, PA3–PA6 bound to the adhesive cell coat secreted by zoospores during encystment, and PA7 and PA8 labeled zoospores and the cyst cell wall. Electron microscopic immunogold labeling of zoospores showed that PA2 bound to the mastigonemes on the anterior flagellum. The MAbs were tested for binding to zoospores and cysts of several isolates of P. aphanidermatum, and to zoospores and cysts of several species of Pythium, Phystophthora, Aphanomyces, and Saprolegnia. The results showed that the antigens recognized by MAbs PA1–PA6 were restricted to P. aphanidermatum, whereas those recognized by PA7 and PA8 occurred on all species tested.