[Mechanisms and implications of the adhesion phenomenon in Aspergillus fumigatus]

During the last few years, several works have demonstrated the fixation of different host proteins on Aspergillus fumigatus conidia. Thus, after incubation in the presence of normal human plasma, the C3 component 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 host, the activation of the alternative pathway seems to be the main mechanism 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 fumigatus conidia interact also with fibrinogen and laminin. These interactions which are mediated by the D domains of fibrinogen and by the fragment 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 determine the adhesion of conidia to the host tissues as suggested by adherence assays of conidia to proteins immobilized onto wells of microtiter plates. Conidia would bind to the fibrin deposits formed on damaged epithelia in response to the inflammatory reaction, or directly to laminin of the subepithelial basement membrane. Finally, different experiments suggested the identity of the binding sites for C3, fibrinogen and laminin at the surface of A. fumigatus conidia.