Pivotal role of carbohydrate recognition domain in self-interaction of CLEC4A to elicit the ITIM-mediated inhibitory function in murine conventional dendritic cells in vitro.

: C-type lectin receptors (CLRs), pattern recognition receptors (PRRs) characteristic with a carbohydrate recognition domain (CRD) in the extracellular portion, mediate crucial cellular functions upon recognition of glycosylated pathogens and self-glycoproteins. CLEC4A is the only classical CLR that possesses an intracellular immunoreceptor tyrosine-based inhibitory motif (ITIM), which possibly transduces negative signals. However, how CLEC4A exerts the cellular inhibition remains unclear. Here, we report that the self-interaction of CLEC4A through the CRD is required for the ITIM-mediated suppressive function in conventional dendritic cells (cDCs). Human type 2 cDCs (cDC2) and monocytes display the higher expression of CLEC4A than cDC1 and plasmacytoid DCs (pDCs) as well as B cells. The extracellular portion of CLEC4A specifically binds to murine cDC cell line expressing CLEC4A, while its extracellular portion lacking the N-glycosylation site or the EPS motif within the CRD reduces their association. Furthermore, the deletions of the EPS motif within the CRD or ITIM in CLEC4A almost completely impairs its suppressive effect on the activation of murine cDC cell line, whereas the absence of the N-glycosylation site within the CRD exhibits the partial inhibition on their activation. On the other hand, antagonistic monoclonal antibody (mAb) to CLEC4A, which inhibits the self-interaction of CLEC4A and its downstream signaling in murine transfectants, enhances the activation of monocytes and monocyte-derived immature DCs upon stimulation with toll-like receptor (TLR) ligand. Thus, our findings suggest a pivotal role of the CRD in self-interaction of CLEC4A to elicit the ITIM-mediated inhibitory signal for the control of the function of cDCs.