THE WI-1 ANTIGEN OF BLASTOMYCES-DERMATITIDIS YEASTS MEDIATES BINDING TO HUMAN MACROPHAGE CD11B CD18 (CR3) AND CD14/

Three genetically related strains of Blastomyces dermatitidis (Bd) yea sts that differ in their expression of WI-1, an immunodominant cell wa ll Ag, were tested for their capacity to bind to human macrophages (M phi) in the absence of serum. These strains included American Type Cul ture Collection (ATCC, Rockville, MD) ATCC 26199, which is virulent fo r mice; an attenuated mutant strain ATCC 60915, which expresses 2.5-fo ld more WI-1 than strain 26199; and an avirulent mutant strain, ATCC 6 0916, which has sixfold more WI-1 than strain 26199. Attachment of bot h mutant strains to M phi was rapid and was maximum after 10 min at 37 degrees C. Attachment of strain 26199 to M phi was approximately 40% of that obtained with the mutants. Binding of Bd to M phi was temperat ure- and Mg2+-dependent, and heat-killed yeasts bound to M phi as well as viable yeasts. Experiments with receptor-specific mAbs demonstrate d that 26199 yeasts bound predominantly to the LPS binding site on CD1 1b/CD18 (CR3). However, the mutants bound to M phi CD14 as well as CR3 . Fab anti-WI-1 inhibited the binding of all strains to M phi by 69 to 78%. Latex microspheres coated with purified WI-1 or a 25-amino acid tandem repeat located within WI-1 also bound to M phi CR3 and CD14. Th ese data demonstrate that: 1) WI-1 is a major ligand on Bd that mediat es attachment of yeasts to human M phi; 2) the binding activity of WI- 1 is located within the 25-amino acid tandem repeat; and 3) binding of Bd yeasts to M phi is mediated through the LPS binding site on CR3 an d CD14.