Effect of intranasal administration of Granulocyte-Macrophage Colony-Stimulating Factor on pulmonary Cryptococcus gattii infection.

Cryptococcosis, caused by infections with C. neoformans and C. gattii, presents a serious threat to global health and necessitates effective treatment strategies. Granulocyte-Macrophage Colony-Stimulating Factor, GM-CSF, is an immune-modulating cytokine that has been utilized clinically to improve host defense against infection; however, the impact of GM-CSF treatment in C. gattii infection has not been elucidated. Our current study aimed to investigate the effect of GM-CSF treatment on pulmonary immune response during C. gattii infection. In response to C. gattii infection, GM-CSF-expressing T helper cells and CD11b+ myeloid were enhanced in the lungs. The intranasal administration of GM-CSF during C. gattii infection significantly reduced pulmonary cryptococcal load, promoted an increase in pulmonary Th17 cells, as well as neutrophil infiltration in the lungs. Exposure of neutrophils to C. gattii in the presence of GM-CSF resulted in an increased neutrophil phagocytosis and fungal killing capacity, generation of reactive oxygen species (ROS), and upregulation of inflammatory cytokines and anti-microbial peptides. Although GM-CSF treatment in C. neoformans-infected mice had a comparable impact on the reduction of lung fungal burden, it resulted in the enhancement of Th1-type cytokine IFN-γ and the activation of M1 macrophages. Altogether, this study demonstrated that the intranasal delivery of GM-CSF has distinct effects on promoting the protection against C. gattii and C. neoformans by activating neutrophil/type-17 immune response and stimulating M1 macrophage/type-1 immunity, respectively.