Antigens ofAspergillus fumigatusexpressed during infection

Abstract

Aspergillus fumigatus secretes an array of antigenic molecules in vitro and in vivo. Recent progresses have been made in the characterization and standardization of A. fumigatus antigens useful for the serodiagnosis of aspergillosis. The chymotrypsin antigen has been purified and can be utilized for the diagnosis of aspergillosis occurring in patients with an immunocompetent B cell population. In the case of immunosuppressed patients suffering from invasive aspergillosis, new methods have been developed to detect the galactofuran containing antigen in the serum. The chemical configuration of this molecule is now known. In contrast to their potential in diagnosis, very little progress has been made on the study of the biochemical and pathoimmunological role of these antigens during the infection process. Two reasons can be advanced for this lack of understanding of the virulence determinants. First of all, antigens studied have been produced in vitro in a dextrose rich medium where pH reaches a value below 5 at maximal growth. These culture conditions are very different from the nutritional environment of the lung, which is a protein-based medium with a slightly basic pH. Antigens expressed under these nutritional conditions are very different from the ones detected in vitro. Second, A. fumigatus is an opportunistic fungus which is characterized by a multifactorial virulence. Gene disruption strategy is not adequate to discriminate the role of a factor in the virulence of the fungus. In contrast, as shown by the studies on two toxins of A. fumigatus, a direct effect of an antigen can be seen directly when several fungal molecules are tested in conjunction on host cells. Key words: Aspergillus fumigatus, antigen, invasive aspergillosis, galactomannan, protease.