Variation of a 470 000 daltons antigen complex and catalase antigen in clinical isolates of Aspergillus fumigatus

Antioxidant systems in the pathogenic fungi of man and their role in virulence

In the last two decades, a variety of fungal antioxidants have attracted considerable interest, largely arising from their hypothetical role as virulence determinants. Melanin is a potent free radical scavenger and in Cryptococcus neoformans, there is now good evidence that the production of melanin is a significant virulence determinant. There is also recent evidence linking melanin biosynthesis to the virulence of Aspergillus fumigatus conidia. Superoxide dismutases are important housekeeping antioxidants and have an additional hypothetical role in virulence; however, although these enzymes have been biochemically characterized from Aspergillus and Cryptococcus, there is as yet no firm evidence that these enzymes are involved in pathogenicity. Catalase production may play some role in the virulence of Candida albicans but this enzyme has not been shown, as yet, to influence the virulence of A. fumigatus. There are some data supporting an antioxidant function for the acyclic hexitol mannitol in C. neoformans, but further investigations are required in this area. Research into the putative antioxidant activities of a range of other fungal enzymes, such as acid phosphatases, remains limited at this time.

The Cu,Zn superoxide dismutases of Aspergillus flavus, Aspergillus niger, Aspergillus nidulans, and Aspergillus terreus: purification and biochemical comparison with the Aspergillus fumigatus Cu,Zn superoxide dismutase

Cu,Zn superoxide dismutases (SODs) have been purified to homogeneity from Aspergillus flavus and A. niger, which are significant causative agents of aspergillosis, and from A. nidulans and A. terreus, which are much rarer causative agents of disease, using a combination of isoelectric focusing and gel filtration fast protein liquid chromatography. The purified enzymes have been compared with the previously described SOD from the most important pathogen in the genus, A. fumigatus (M. D. Holdom, R. J. Hay, and A. J. Hamilton, Free Radical Res. 22:519-531, 1995). The N-terminal amino acid sequences of the four newly purified enzymes were almost identical and demonstrated homology to known Cu,Zn SODs from a range of organisms including that from the previously described SOD from A. fumigatus. SOD activity was detectable in the culture filtrates of all species, and intracellular Cu,Zn SOD activity as a proportion of total protein was highest in early-log-phase cultures. The specific activities of the purified enzymes were similar, and all four of the newly described enzymes were inhibited by potassium cyanide and diethyldithiocarbamate, known Cu,Zn SOD inhibitors. Sodium azide and o-phenanthroline demonstrated inhibition at concentrations from 5 to 30 mM, and EDTA also exhibited a varying degree of inhibition of SOD activity. However, there were differences in the nonreduced molecular masses, the reduced molecular masses, and the isoelectric points of the four newly described SODs and the A. fumigatus enzyme; these varied from 55 to 123 kDa, 17.5 to 19.5 kDa, and 5.0 to 5.9, respectively. Of particular note was the observation that the A. fumigatus enzyme was thermostable compared with the SODs from the other species; in addition, the A.fiumigatus enzyme retained all of its activity at 37 degrees C relative to 20 degrees C, whereas the SODs of A. nidulans and A. terreus lost significant activity at the higher temperature. Aspergillus Cu,Zn SOD plays a hypothetical role in the avoidance of oxidative killing mechanisms, and our data suggest that the thermotolerant A. fumigatus Cu,Zn SOD would be more effective in such a protective system than, for example, the equivalent enzyme from the more rarely pathogenic A. nidulans.

Immunodiagnosis of aspergillosis

Aspergillus species are ubiquitous fungi and have been implicated as the causative agents of a variety of lung disorders in humans. These disorders include allergic, saprophytic, and systemic manifestations. The allergic disorders mainly affect atopic persons, and invasive or systemic diseases affect immunosuppressed individuals. Immunodiagnosis can help the practitioner diagnose these diseases. Demonstration of circulating antibodies is a useful criterion, but the lack of dependable and standardized antigens is a limiting factor in the diagnosis of most Aspergillus-induced diseases. Despite this limitation, however, immunodiffusion and enzyme-linked immunosorbent assays have been widely used for the detection of antibodies in the sera of patients with aspergillosis. Similarly, crude and semipurified antigens are being used to demonstrate skin hypersensitivity in patients, and several methods have been useful in the detection of antigenemia in patients with invasive aspergillosis. With a growing number of reports on the incidence of aspergillosis and an increase in the number of immunosuppressed individuals in the population, more rapid methods and more reliable reagents for immunodiagnosis are needed. With recent attempts at obtaining reliable reagents for through hybridoma technology and molecular biological techniques, substantial progress toward efficient immunodiagnosis may be achieved.

Murine monoclonal antibodies binding to the specific antigens of Aspergillus fumigatus associated with allergic bronchopulmonary aspergillosis

Four murine monoclonal antibodies, which were produced against Aspergillus fumigatus antigens using hybridoma technology, reacted with different antigenic components of A. fumigatus, and in turn these antigens showed reactivity with the sera from allergic bronchopulmonary aspergillosis (ABPA). All four antibodies were of IgM isotype. These antibodies reacted against eight antigen preparations from three different strains of A. fumigatus by enzyme-linked immunosorbent assay (ELISA). Only two of four antibodies reacted with the antigens in crossed immunoelectrophoresis (CIE), rocket immunoelectrophoresis, and agar gel double diffusion. In western blot analysis it was found that the antigenic components reacting with the monoclonal antibodies were mostly of the low molecular weight components of A. fumigatus antigens. These components also showed binding to both IgG and IgE antibodies in the sera of ABPA patients, but failed to show any reactivity with sera from aspergilloma patients. Hence these antigenic components may be of diagnostic significance and can be isolated using immunoaffinity chromatography.