immunology of infectious and parasitic diseases - XXXVII Congress ...

ENCAPSULATED Cryptococcus neoformans EVADES INFLAMMASOME
ACTIVATION
PEDRO H. V. SAAVEDRA 1 ; MANUELLA CAPPARELLI 1 ; LARISSA F. MATOS 1 ;
DARIO S. ZAMBONI 2 ; ARTURO CASADEVALL 3 ; KELLY G. MAGALHAES 1 ;
ANAMELIA L. BOCCA 1
1 Department of Cell Biology, University of Brasília, Brasília, Brazil; 2 Department
of Cell Biology and Microbial Pathogenesis, Medical School of Ribeirão Preto,
University of São Paulo, São Paulo, Brazil 3 Department of Microbiology and
Immunology, Albert Einstein College of Medicine, Bronx, NY, USA
Introduction: Cryptococcus neoformans is an encapsulated yeast widely
distributed around the globe, capable of causing pulmonary infection and
meningitis in immunocompromised individuals. Its capsule is well known for
conferring C. neoformans the ability to evade host immune system, leading to
its proliferation. Regarding the importance of initial innate immune response to
cryptococcal infections, we decided to investigate if C. neoformans is capable of
activating the inflammasome as well as the role of its capsule in this pathway.
Methods and Results: In order to verify whether C. neoformans could trigger
inflammasome activation, bone marrow-derived macrophages (BMMs) were
infected with wild type C. neoformans or its acapsular mutant. Our results
showed that acapsular mutant of C. neoformans, but not the wild type, induced
IL-1β secretion. Flow cytometry and western blot analysis revealed that
caspase-1 is activated upon infection with acapsular but not with WT C.
neoformans. To understand the role of inflammasome proteins in IL-1β
secretion induced by acapsular C. neoformans, WT, Asc -/- , Casp1 -/- , Nlrp3 -/- and
Nlrc4 -/- BMMs were infected. IL-1β secretion was dependent on the NLRP3-
ASC-Caspase-1, but independent on the NLCR4 inflammasome. In addition,
inflammasome proteins were dispensable for fungal uptake or killing as
demonstrated by CFU analysis. The mechanisms underlying IL-1β processing
and release by C. neoformans infection were dependent on reactive oxygen
species (ROS), lysosomal destabilization and Syk tirosine kinase signaling,
based on inhibition assays. Interestingly, cells treated with IL-1β in a dosedependent
manner were unable to restrict intracellular yeasts, however, the rate
of infection diminished significantly compared to untreated cells.
Conclusion: Taken together, our data show for the first time that acapsular C.
neoformans activates the NLRP3 inflammasome and IL-1β secretion in a
caspase-1 dependent manner. The mechanisms that orchestrate this event rely