Paracoccidiodes brasiliensis, the agent of paracoccidioidomycosis, when grown in a synthetic medium, expresses at the cell surface of both yeast and mycelial forms acidic glycoconjugates containing N‐acetlyneuraminic acid units. Sialic acids were extracted using mild hydrolytic conditions, and were identified by thin‐layer and gas chromatography, standard colorimetry, reaction with periodate‐resorcinol and mass spectrometry. Their surface location was inferred from fluorescent‐lectin (Limulus polyphemus agglutinin) binding to whole cells abrogated by previous treatment with neuraminidase. Expression of sialic acids on virulent yeast forms of P. brasiliensis (3.7 × 106 residues per cell) may inhibit fungal phagocytosis during early infection, when the immunological response is still being built up.
The surface anionogenic groups and sialoglycoconjugate structures of Paracoccidioides brasiliensis yeast forms were analysed by cell microelectrophoresis, binding assays with lectins and viral particles, ultrastructural cytochemistry, enzymic digestion and flow cytof luorimetry. P. brasiliensis yeast forms, particularly the budding primordia, reacted strongly with cationized ferritin. Binding assays showed that the reaction with sialic-acid-specif ic Limax flaws lectin (LFA) was distributed over the entire P. brasiliensis cell wall. Treatment of yeast forms with neuraminidase significantly reduced their negative surface charge and LFA labelling, which suggests that sialic acid residues are major anionogenic groups exposed on the P. brasiliensis surface. Furthermore, after neuraminidase treatment, labelling with Arachis hypogaea (peanut) agglutinin increased due to unmasking of subterminal /I-D-galactopyranosyl residues. The sialic acid linkages to galactose are a2,6 and a283 as assessed, respectively, by fungal attachment to M1/5 and M1/5 HS8 strains of influenza A virus and binding of Sambucus niger and Maackia amurensis agglutinins. The d , 6 linkage clearly predominated in both experiments. Flow cytof luorimetry analysis revealed the heterogenicity of P. brasiliensis yeast cell populations, which comprised young and mature budding yeasts. Both express binding sites to LFA and Limulus polyphemus agglutinin.
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