MECHANISMS AND IMPLICATIONS OF THE ADHERE NCE PHENOMENONS IN ASPERGILLUS-FUMIGATUS

During the last few years, several works have demonstrated the fixatio n of different host proteins on Aspergillus fumigatus conidia. Thus, a fter incubation in the presence of normal human plasma, the C3 compone nt of complement is detected at the surface of conidia. In fact, most of the C3 deposited on conidia is converted in C3b or iC3b which would facilitate their phagocytosis by the macrophages. In the non immune h ost, the activation of the alternative pathway seems to be the main me chanism of the activation of the complement system by the conidia, but the participation of the classical pathway initiated by the fixation of the C-reactive protein has also been suggested. Aspergillus fumigat us conidia interact also with fibrinogen and laminin. These interactio ns which are mediated by the D domains of fibrinogen and by the fragme nt P1 of laminin, are specific. The number of fibrinogen binding sites at the surface of conidia has been calculated to be 1200 by cell, and the dissociation constant 2.2 x 10(-7) M. These interactions could de termine the adhesion of conidia to the host tissues as suggested by ad herence assays of conidia to proteins immobilized onto wells of microt iter plates. Conidia would bind to the fibrin deposits formed on damag ed epithelia in response to the inflammatory reaction, or directly to laminin of the subepithelial basement membrane. Finally, different exp eriments suggested the identity of the binding sites for C3, fibrinoge n and laminin at the surface of A. fumigatus conidia.