Curdlan induces selective mast cell degranulation without concomitant release of LTC_4, IL-6 or CCL2

Mast cells are sentinel cells with a tissue-specific localization in the interface between the host and the external environment. Their quick and selective response upon encountering pathogens is part of the innate host response and typically initiates the following adaptive immune response. Among several pattern recognition receptors (PRRs) involved in the recognition of pathogens by mast cells, the C-type lectin receptor Dectin-1 has been associated with the recognition of fungi. Our previous studies have shown that mast cells are the predominant cell type expressing Dectin-1 in human skin, and they also recognize and respond to Malassezia sympodialis by producing cytokines connected to the innate host response and upregulating the expression of Dectin-1. In the present study, we investigated mast cell responses to Curdlan, a β-glucan that acts as an agonist for the fungi receptor Dectin-1, and found a unique response pattern with induced degranulation, but surprisingly without synthesis of Leukotriene C₄, IL-6 or CCL2. Since mast cells are the predominant Dectin-1 expressing cell in the human skin, this study suggests that mast cell degranulation in response to fungi is an important part of the first line of defense against these pathogens.