IMMUNOLOGICAL RECOGNITION OF A 25-AMINO-ACID REPEAT ARRAYED IN TANDEMON A MAJOR ANTIGEN OF BLASTOMYCES-DERMATITIDIS

A 120-kD glycoprotein antigen abundantly expressed on Blastomyces derm atitidis yeasts is a target of cellular and humoral immune responses i n human infection. To investigate the antigen and immune response more carefully at the molecular level, we screened an expression library f rom B. dermatitidis to identify clones that encode this antigen, desig nated WI-1. A 942-bp cDNA was isolated by immunologic screening with p olyclonal, rabbit anti-WI-1 antiserum. Northern hybridization analysis showed that the cDNA hybridized to yeast message congruent-to 3.9 kb. DNA and deduced protein sequence analysis of the clone demonstrated a 25-amino acid repeat arrayed in tandem, present in 4.5 copies near th e 5' end, and rich in predicted antigenic epitopes. Further analysis s howed strong homology in these tandem repeats with invasin, an adhesin of Yersiniae. Cloned cDNA was used to express a 30-kD fusion protein strongly recognized in western blots by rabbit anti-WI-1 antiserum, an d by sera from all 35 blastomycosis patients studied. The fusion prote in product of subcloned cDNA encoding only the tandem repeat also was strongly recognized in western blots by sera from the 35 blastomycosis patients, but not by sera from 10 histoplasmosis and 5 coccidioidomyc osis patients. An antigen-inhibition radioimmunoassay showed that the tandem repeat alone completely eliminated rabbit and human anti-WI-1 a ntibody binding to radiolabeled native WI-1. From these results, we co nclude that the 25-amino acid repeat of WI-1 displays an immunodominan t B cell epitope, and that the carboxyl-terminus of the molecule exhib its an architecture that may promote adhesion of Blastomyces yeasts to host cells or extracellular matrix proteins and ultimately provide a clearer picture of the molecular pathogenesis of blastomycosis.