Cell walls from avirulent variants of Histoplasma capsulatum lack alpha-(1,3)-glucan.

Cell wall composition of isogenic virulent-avirulent strain pairs of Histoplasma capsulatum varied markedly with respect to alpha-(1,3)-glucan content. When yeast cell walls were fractionated by standard techniques, the avirulent strains contained up to 1,000-fold less alpha-(1,3)-glucan than did their virulent parents. No alpha-(1,3)-glucan could be detected on the surface of the avirulent strain yeast cells if we used a mouse monoclonal antibody that recognized this polymer. A similar relationship between virulence and alpha-(1,3)-glucan has been described for Paracoccidioides brasiliensis. alpha-(1,3)-Glucan is also found in several other pathogenic fungi and may thus be an important common virulence determinant.