Cell wall antigens in Aspergillus fumigatus

The Aspergillus cell wall contains most of the antigens secreted by the fungus during its active in vitro or in vivo growth. These antigens, which bind to the IgE and IgG of allergic and aspergilloma patients or are secreted in the biological fluids of patients with invasive aspergillosis, are of primary importance in the diagnosis of aspergillosis. Located at the interface between host and pathogen cells, the fungal cell wall plays a major role during fungal invasion. It contains several surface receptors involved in adhesion of the fungus to host proteins and cells. Some of the wall antigens are also directly involved in the colonization of the host tissues by the fungus. Very few of these putative virulence factors have been purified until now. A 33-kDa alkaline protease of the subtilisin family can hydrolyze several extracellular matrix proteins such as collagen, fibrinogen, elastin. However, gene disruption experiments have shown that protease-deficient mutants are still able to infect mice. An 18-kDa antigen, which has been detected in the urine of patients with invasive aspergillosis, is present in vivo in the lung of mice infected with A. fumigatus. It has a ribonuclease activity that cleaves a single phosphodiester bond in a highly conserved region of the ribosomal RNA. Its role in the virulence of A. fumigatus has not been demonstrated until now. Biochemical and molecular characterization of the wall antigenic aggressins should be pursued.