Immunocytochemical localization of in vitro binding of human fibrinogen to Candida albicans germ tube and mycelium.

In vitro fixation of human fibrinogen to different morphological stages of Candida albicans was examined immunocytochemically. When detected by fibrinogen latex microspheres or gold particles by scanning electron microscopy, fibrinogen-binding sites were found on the surface of germ tubes and mycelium, but not on blastospores. With transmission electron microscopy, fibrinogen-binding sites appeared associated with the flocculent surface layer, and increased during growth of germ tubes. Prefixation of C. albicans with formaldehyde decreased binding of fibrinogen, and pretreatment with mercaptoethanol and pronase abolished it. On thin sections of low temperature "Lowicryl K4M" -embedded organisms, gold particles were arranged in the form of clusters which extended from the surface through the cell wall. In contrast, the inner cell wall layers were weakly labelled. Labelling was also detected in the cytoplasm of germ tube, suggesting that fibrinogen receptors were synthesized during germ tube formation. In view of the importance of filamentous forms in host tissue adherence and colonization, the role of fibrinogen as a ligand for binding of C. albicans to epithelial cells was postulated.