Contribution of Laccase Expression to Immune Response against Cryptococcus gattii Infection

Cryptococcosis is an infectious disease caused by two fungal species, Cryptococcus neoformans and Cryptococcus gattii While C. neoformans affects mainly immunocompromised patients, C. gattii infects both immunocompetent and immunocompromised individuals. Laccase is an important virulence factor that contributes to the virulence of C. neoformans by promoting pulmonary growth and dissemination to the brain. The presence of laccase in C. neoformans can shift the host immune response toward a nonprotective Th2-type response. However, the role of laccase in the immune response against C. gattii remains unclear. In this study, we characterized laccase activity in C. neoformans and C. gattii isolates from Thailand and investigated whether C. gattii that is deficient in laccase might modulate immune responses during infection. C. gattii was found to have higher laccase activity than C. neoformans, indicating the importance of laccase in the pathogenesis of C. gattii infection. The expression of laccase promoted intracellular proliferation in macrophages and inhibited in vitro fungal clearance. Mice infected with a lac1Δ mutant strain of C. gattii had reduced lung burdens at the early but not the late stage of infection. Without affecting type-1 and type-2 responses, the deficiency of laccase in C. gattii induced cryptococcus-specific interleukin-17 (IL-17) cytokine, neutrophil accumulation, and expression of the neutrophil-associated cytokine gene Csf3 and chemokine genes Cxcl1, Cxcl2, and Cxcl5 in vivo, as well as enhanced neutrophil-mediated phagocytosis and killing in vitro Thus, our data suggest that laccase constitutes an important virulence factor of C. gattii that plays roles in attenuating Th17-type immunity, neutrophil recruitment, and function during the early stage of infection.