CLEC12B was first identified as an inhibitory receptor on myeloid cells that counteracts NK cells-mediated cytotoxicity. CLEC12B is a C-type Lectin Receptor (CLR) which possesses an ITIM domain, but ligand and downstream signaling are largely unknown. Over the past 30 years, an antigen-presenting function of melanocytes has emerged due to their dendritic nature, their strategic position in the skin and their phagocytic capacity. In a vitiligo context, our team has shown that CXCR3B activation, the receptor for immune chemokines CXCL9, CXCL10 and CXCL11, induces apoptosis of cultured human melanocytes. The remaining melanocytes, activated by the IFNγ production, express co-stimulatory markers which trigger T cell proliferation and subsequent anti-melanocytic immunity. Recent results from our team have shown that CLEC12B is mainly expressed in human melanocytes and plays an important role in the regulation of skin pigmentation, but also in melanoma proliferation.
In this project, we set out to determine the role of CLEC12B in skin immunity using primary human melanocytes from healthy donors. We demonstrate that CLEC12B is critical in production of IFNγ and innate chemokines CXCL9, CXCL10 and CXCL11 by melanocytes, as shown by our regulation of CLEC12Bexpression using silencing or overexpression techniques. This regulation was driven by the phosphorylation of CLEC12B’s ITIM domain as shown using CLEC12B mutated form of the gene. Furthermore, not only can CLEC12B drive melanocyte chemokine production, but it is also capable of directly increase chemoattraction of immune cells in the skin and therefore trigger a long-term adaptative immunity. From a signaling point of view, we show that CLEC12B modulates IFNγ signaling pathway through the STAT1/IRF1 axis. Moreover, CLEC12B potentiates the effect of IFNγ in primed melanocytes, thus inducing a larger production of innate chemokines and subsequent greater chemoattraction of immune cells. In addition, we have demonstrated that CLEC12B directly interacts with Staphylococcus aureus and Escherichia coli and modulates an innate immune response against these opportunistic bacteria found on the skin through the STAT1/IRF1/CXCL9 axis. Finally, we have shown that CLEC12B senses motifs present on melanocytes, fibroblasts, and both pro- and anti-inflammatory macrophages, but its exact ligand(s) still remains to be identified. Together, these results demonstrate that CLEC12B is an important player in innate skin immunity by modulating the production of IFNγ and immune chemokines, and in adaptative immunity by modulating the migration ability of immune cells through the phosphorylation of its ITIM domain. This mechanism is of great interest as IFNγ and cellular recruitment are key initial steps involved in inflammation of many skin pathologies, making this receptor an interesting therapeutic target for the treatment of infectious diseases, inflammatory and pigmentary skin disorders, as well as cancer; all which may be able to be directly immuneregulated by CLEC12B on melanocytes. This exciting novel prospect remains to be tested in future studies.
Key words :
CLEC12B, C-type lectin receptor, melanocyte, immunity, IFNγ, chemokines
Dr. Laurent Boyer, DR Inserm, C3M, Université Côte d’Azur.
Pr. Marie-Dominique Galibert, PU-PH, Institut de Génétique et Développement de Rennes (IGDR), CHU et Université de Rennes 1.
Dr. Marc Vocanson, CR Inserm, Centre International de Recherche en Infectiologie (CIRI), Lyon.
Dr. Yoann Rombouts, CR CNRS, Institut de Pharmacologie et de Biologie Structurale (IPBS), Université de Toulouse.
Pr. Thierry Passeron, PU-PH, C3M, CHU de Nice, Université Côte d’Azur.
Dr. Meri K. Tulic, DR Inserm, C3M, Université Côte d’Azur.