Localization of fungal fimbriae by immunocytochemistry in pathogenic and nonpathogenic isolates of Venturia inaequalis

Pathogenic and nonpathogenic isolates of Venturia inaequalis were grown in liquid culture. Hyphae were treated with two types of fimbrial antiserum (A U- and AV-1) and examined by immunofluorescent microscopy, in order to esta blish the distribution of fimbrial epitopes in whole cell mounts. The AV-1 antiserum was specific for the glycoprotein subunits while the AU-antiserum was specific for the protein moieties present on the fimbriae of Mycobotry um violaceum. The use of fimbrial antiserum with immunocytochemistry and tr ansmission electron microscopy demonstrated a clear distinction between pat hogenic and nonpathogenic isolates of V. inaequalis, based on the appearanc e of the fungal cell wall and the distribution of fimbrial epitopes labeled with AV-1 antiserum and immunogold complex. In actively growing hyphae of the pathogenic isolate, characterized by distinct cellular organelles, smal l vacuoles, and lipid bodies, fimbrial epitopes were concentrated in the fu ngal cell wall and were present minimally on the outer surface. In contrast , actively growing hyphae of the nonpathogenic isolate of V. inaequalis had extensive fine hair-like protrusions in the fungal cell wall which labeled with the AV-1 antiserum and immunogold. The distribution of fimbrial epito pes in V. inaequalis was highly dependent on the developmental growth stage of the fungal mycelium. Aging mycelia in both the pathogenic and nonpathog enic isolates of V. inaequalis were characterized by a large central vacuol e and no label. In the pathogenic and nonpathogenic isolates of V. inaequal is grown in vitro, the distribution of fimbrial glycoprotein epitopes provi ded a more complex profile than that seen in M. violaceum.