Strain-specific variation in virulence and host-immune modulation across the Cryptococcus gattii species complex.

Cryptococcus gattii is an environmental yeast capable of causing severe infections in immunocompetent hosts. Its virulence mechanisms remain less characterized than those of C. neoformans. This study aimed to evaluate the expression of major virulence factors and the immunomodulatory potential of eight C. gattii strains representing five genotypes and multiple sequence types (STs). Virulence traits-including capsule thickness, melanin and laccase production, phospholipase, hemolysin, urease, and DNase activities-were assessed using standardized in vitro assays. In vivo pathogenicity was evaluated in Galleria mellonella, and macrophage responses were analyzed via nitric oxide (NO) production and cytokine gene expression in J774.A1 cells. Capsule and melanin production varied significantly across strains, with VGI/ST106 and VGII/ST7 showing the highest levels, respectively. VGIV/ST336, VGI/ST106, and VGVI/ST556 induced greater larval mortality than the reference C. neoformans strain (VNI/ST5), while VGII strains exhibited ST-dependent virulence. Most strains inhibited NO production in macrophages, except VGI/ST106, which enhanced it. Cytokine expression remained low in the absence of inflammatory priming. These findings reveal substantial phenotypic variability in virulence and immune modulation among C. gattii strains. Further investigation into strain-specific host interactions may helpthe development of targeted antifungal strategies and improve clinical management of cryptococcosis.