Cryptococcus gattii and C. neoformans are very closely related fungi, but when it comes to the infections they cause there are some important differences. In their study in mBio this week, Ngamskulrungroj et al. drilled down into those differences using a mouse model and found that C. gatii may be a bigger problem for the lungs because it suppresses the immune response there.
Between them, C. gattii and C. neoformans are the most common fungal pathogens that cause fatal central nervous system infections in humans. But they don't necessarily target the same groups of people: C. neoformans is classified as an AIDS-defining opportunistic pathogen, while C. gattii is classified as a primary pathogen. What's more, C. gatii appears to specialize in lung infections. Only 35% of C. neoformans patients suffer from a lung infection, while 70% of C. gattii patients do.
In their study, Ngamskulrungroj et al. infected mice intravenously or through the respiratory route with various strains of C. gattii and C. neoformans. When infected through their lungs, C. neoformans killed mice through a brain infection and C. gattii killed them through a lung infection, showing that C. gattii probably cannot cause fulminant (sudden) meningoencephalitis when infected through the lungs. This suggested to the authors that the lungs mount a stronger protective immune response to C. gattii than to C. neoformans, preventing C. gattii from getting into the bloodstream and the brain. They also observed that C. gattii was superior to C. neoformans at growing within the lungs, reaffirming what is commonly observed in patients: C. neoformans to the brain, C. gattii to the lungs.