C-type Lectin Receptor Expression on Human Basophils and Effects of Allergen-Specific Immunotherapy

Basophils are emerging as immunoregulatory cells capable of interacting with their environment not only via their characteristic IgE-mediated activation, but also in an IgE-independent manner. Basophils are known to express and respond to stimulation via TLR2, TLR4, DC-SIGN and DCIR, but whether basophils also express other C-type lectin receptors (CLRs) is largely unknown. In this study, we investigate the CLR expression profile of human basophils using multicolour flow cytometry. As FcRs as well as some CLRs are associated with allergen recognition and shown to be involved in subsequent immune responses, the expression of CLRs and FcRs on peripheral blood basophils, as well as their frequency, was monitored for 1 year in subjects undergoing subcutaneous allergen-specific immunotherapy (AIT). Here, we show that human basophils express CLECSF14, DEC205, Dectin-1, Dectin-2 and MRC2. Furthermore, we demonstrate that the frequencies of basophils expressing the allergy-associated CLRs Dectin-1 and Dectin-2 were significantly reduced after 1 year and 8 weeks of AIT, respectively. In contrast, the frequency of basophils positive for FcγRII, as well as the fraction of total basophils, significantly increased after 1 year of AIT. The herein demonstrated expression of various CLRs on basophils, and their altered CLR and FcR expression profile upon AIT, suggest yet unexplored ways by which basophils can interact with antigens and may point to novel immunoregulatory functions targeted through AIT.