Recognition of fibrinogen and basement membrane components as mediators of the adherence of Aspergillus fumigatus conidia

Abstract

In order to elucidate the molecular basis of the adherence of Aspergillus fumigatus to epithelial surfaces, we investigated the interactions between this opportunistic fungus and some host adhesive proteins. Among the presumptive ligands, our attention was focused on fibrinogen and laminin which are known to mediate the attachment of numerous microorganisms to the host tissues. These interactions were first demonstrated using soluble human fibrinogen and laminin extracted from the Englebreth-Holm-Swarm sarcoma tumour. By immuno fluorescence and electron microscopy, the binding of these two proteins was detected mainly at the surface of conidia, associated with the protrusions of the outer cell wall layer of resting conidia, or uniformly distributed over the cell wall of swollen conidia and of mother cells of germ tubes. Moreover, these interactions seemed to be involved in the adherence of conidia. Conidia strongly adhered to fibrinogen or laminin but not to fibronectin or heparan sulfate proteoglycans immobilized in wells of polystyrene microtitre plates. Adhesion was dose dependent and specific. Binding sites appeared to be located in the D domains of the fibrinogen molecule and in the fragment P 1 of laminin. In addition, flow cytometric analysis of the binding of fibrinogen demonstrated that the expression of binding sites at the surface of conidia correlated with their maturation, and confirmed the specificity of the interaction. Binding was inhibited by unlabelled fibrinogen and by basement membrane laminin, suggesting the existence of a common receptor or steric hindrance of the receptor sites by the unrespective ligand. However, precise identification of the adhesiotope failed since no inhibition could be obtained by the different synthetic petides used nor by the sugars tested.