Interaction of Histoplasma capsulatum Yeasts with Galactosylated Surface Molecules of Murine Macrophages

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Background. Histoplasma capsulatum (H.c.) yeast-cell binding to glycosylated surface molecules of murine macrophages was studied using attachment inhibition assays with different carbohydrate-treated H.c. yeast cells and participation of galactose and its derivatives as main sugar inhibitor was always demonstrated. Methods. Liposomes incorporated with macrophage membrane proteins (MMP) were constructed to test involvement of macrophage surface glycoprotein molecules in H.c. binding. Yeasts attachment to MMP liposomes was successfully evaluated by ELISA method. Afterward, inhibition of H.c. yeast-cell attachment to [1,2- 3H(N)]-cholesterol-MMP liposomes was monitored by radioactivity counting of the yeast-liposome pellet centrifuged at 500 g for 30 min when yeasts were previously incubated with different sugars. Other inhibition attachment assays using light microscopy and modified ELISA adapted to peritoneal or alveolar macrophage monolayers were also performed to determine inhibition mediated by carbohydrates. In these assays, Candida albicans (C.a.) was used as control of another type of yeast containing a lectin-like molecule. Results. Histoplasma capsulatum yeasts attachment to MMP liposomes showed important decrease of radioactive counts when treated with galactose and lactose molecules. Light microscopy and modified ELISA confirmed inhibition mediated by galactose and its derivatives either in peritoneal or alveolar macrophages, and β-galactose was better recognized than its α-anomer. In contrast, C.a. attachment to peritoneal or alveolar macrophages was not markedly affected by galactose-derivative molecules. Conclusions. Results suggest presence of a lectin-like component in H.c. yeast cells and reveal involvement of galactosylated surface molecules of murine macrophages as specific-sugar (ligand) residues recognized by the fungal lectin.