Two Aspergillus species, A. flavus and A. fumigatus - a comparative study of their conidial surface properties and immunological reactivities
Résumé
Though belonging to the Aspergillus genus, Aspergillus fumigatus is the major causative agent of fatal invasive aspergillosis, the systemic infection in immunocompromised, while A. flavus causes keratitis, a superficial health hazardous infection in immunocompetent individuals. In the present study, we have been exploring these two Aspergillus species in understanding differences in their preferred sites of infection. Structurally, there was a difference in their conidial sizes. A. fumigatus conidia were uniformly labelled by calcofluor white, negative for FITC conjugated Concanavalin-A or wheat-germ agglutinin labelling, while A. flavus conidia showed heterogenous labelling. The A. fumigatus conidia surface was covered by a uniform rodlet layer whereas A. flavus conidia showed heterogeneity; some conidia showing rodlet layer, but others with additional amorphous structure. A. flavus conidial cell wall contained significantly higher amount of chitin and lower amount of glucan in the alkali-insoluble fraction compared to A. fumigatus conidial cell wall. Whereas, in the mycelial morphotype, the A. flavus cell wall showed a significantly lower amount of glucan in cell wall and higher amounts of chitin and galactosamine containing polysaccharide in the alkali-insoluble fraction. A. fumigatus condia failed to activate human monocyte derived macrophages, dendritic cells and isolated neutrophils, but A. flavus conidia were immuno-stimulatory in their effect. Interestingly, though macrophages secreted both pro- and anti-inflammatory cytokines, dendritic cells and neutrophils secreted only IL-8 upon A. flavus conidial interaction. These observations may reason for their preferred mode and thus the site of infection