Dectin-1 Expression is Altered by Fungal Infection, Polymicrobial Sepsis, and Glucan Administration.

Glucans are fungal cell wall PAMPs that promote survival in polymicrobial and candidal sepsis. Dectin-1 is the primary PRR for glucans. The goals of the present study were to characterize 1) the effects of fungal infection on Dectin-1; 2) the effects of polymicrobial sepsis in the presence and absence of glucan on Dectin-1; 3) the effects of systemic administration of glucans on Dectin-1; and 4) the intracellular trafficking of glucans. Mice were either systemically infected with Candida albicans, or made septic by CLP with and without glucan phosphate (GP) injection, or injected with GP. Flow cytometry was performed to assess cell surface Dectin-1 expression. C. albicans sepsis resulted in an increase in the percentage of Dectin-1 positive (Dectin+) blood and splenic leukocytes by increasing the percentage of neutrophils. C. albicans infection increased the percentage of Dectin+ splenic T cells. CLP decreased the percentage of highly Dectin-1 positive leukocytes in the blood by decreasing the percentage of Dectin+ neutrophils. GP treatment in sepsis further decreased the percentages of Dectinhigh blood leukocytes and Dectin+ neutrophils. CLP decreased the percentage of Dectin+ splenic leukocytes by decreasing the percentage of splenic macrophages. GP administration to CLP mice further decreased the percentage of Dectin+ splenocytes by decreasing the percentage of Dectin+ macrophages. Administration of GP resulted in a prolonged decrease in the percentage of Dectinhigh blood leukocytes. The changes in Dectin-1 expression with GP were because of decreases in the percentage of Dectin+ neutrophils and monocytes. In the trafficking studies, macrophages were incubated with fluorescent labeled glucans and then stained for intracellular organelles and signal transduction molecules. Cells were imaged using confocal microscopy. GP is internalized by clathrin and trafficked to the Golgi apparatus. GP internalization is regulated but not dependent on caveolin-1. GP co-localized with SRA, TLR2, and PI3K/p85. The trafficking of laminarin and particulate glucan is similar. We speculate that loss of cell surface Dectin-1 may be important in the protection conferred by glucans in sepsis. Additionally, intracellular trafficking and interaction with signaling components may be important steps in modulation of cellular function by glucan-pattern recognition receptor complexes