Novel antigenic determinants from peptidorhamnomannans of Sporothrix schenckii

Antisera were raised in rabbits against acetone-dried yeast-like and mycelium forms of Sporothrix schenckii. These antisera were tested for immunoprecipitation of peptidorhamnomannans isolated from both cell types. Both antisera reacted strongly with S.schenckii peptidorhamnomannans, but the reactions were weak with beta-eliminated peptidopolysaccharides. These antisera did not recognize the Saccharomyces cerevisiae mannoprotein, and reacted poorly with Ceratocystis (Ophiostoma) stenoceras cell wall glycopeptides. Since beta-eliminated glycopeptides were poorly reactive, we investigated the activity of O-glycosidically linked oligosaccharides which were liberated from the peptidorhamnomannans by mild alkaline hydrolysis, using a hapten inhibition test. The rates of inhibition showed that the immunodominant epitopes in O-linked tetra- and pentasaccharides had the following novel structures: alpha-L-Rhap (1-->4)-alpha-D-GlcpA and alpha-L-Rhap(1-->4)-[alpha-L-Rhap(1-->2)]alpha-D-GlcpA . Results suggest that peptidorhamnomannans or synthetic antigens bearing these epitopes should be used for the specific detection of anti-S.schenckii antibodies rather than the long-chain N-linked polysaccharides.