Strain dependent variation of immune responses: how fungal origin and biodiversity shape commensalism or pathogenicity

For over a century microbiology and immunology have classified microorganisms in pathogenic or non-pathogenic. This definition, clearly relevant at the level of strain and species for most bacteria, has never been probed in fungal species. Understanding the nature of fungal pathogenesis will result in developing more effective therapies for fighting invasive fungal infection. Currently, several studies attempt to address pathogenicity mechanisms using different strains as a model. This study was designed to explore immune-based diversity of Aspergillus spp, Candida spp and Saccharomyces cerevisiae fungal strains derived from different ecological niches. The in-vitro preliminary classification and characterization of fungal biodiversity in inducing immune responses led us to start the investigation on how/if the different cell mediated immunogenicity could result in differences in trained immunity properties of the tested strains. Our results show a wide strain-dependent variation of the immune response elicited indicating that different isolates possess diverse virulence and infectivity. Thus, the definition of markers of inflammation or pathogenicity cannot be generalized. The profound understanding of the molecular mechanisms subtending the different immune responses will result solely from the comparative study of strains with extremely diverse properties.