Interaction of murine macrophage‐membrane proteins with components of the pathogenic fungus Histoplasma capsulatum

The interaction of macrophage‐membrane proteins and histoplasmin, a crude antigen of the pathogenic fungus Histoplasma capsulatum, was studied using murine peritoneal macrophages. Membrane proteins were purified via membrane attachment to polycationic beads and solubilized in Tris–HCl/SDS/DTT/glycerol for protein extraction; afterwards they were adsorbed or not with H. capsulatum yeast or lectin binding‐enriched by affinity chromatography. Membrane proteins and histoplasmin interactions were detected by ELISA and immunoblotting assays using anti‐H. capsulatum human or mouse serum and biotinylated goat anti‐human or anti‐mouse IgG/streptavidin‐peroxidase system to reveal the interaction. Results indicate that macrophage‐membrane proteins and histoplasmin components interact in a dose‐dependent reaction, and adsorption of macrophage‐membrane proteins by yeast cells induces a critical decrease in the interaction. Macrophage‐membrane glycoproteins with terminal D‐galactosyl residues, purified by chromatography with Abrus precatorius lectin, bound to histoplasmin; and two bands of 68 kD and 180 kD of transferred membrane protein samples interacted with histoplasmin components, as revealed by immunoblot assays. Specificity for β‐galactoside residues on the macrophage‐membrane was confirmed by galactose inhibition of the interaction between macrophage‐membrane proteins and histoplasmin components, in competitive ELISA using sugars, as well as by enzymatic cleavage of the galactoside residues.