Functions coreceptor to limit the innate immune responses to viral infections; signaling occurs via FCER1G (PubMed:16735691, PubMed:19564354). Down-regulates the production of IFNA1, IFNA2, IFNA4, IFNB1 and TNF by plasmacytoid dendritic cells that have been exposed to influenza virus or cytidine-phosphate-guanosine (CpG) dinucleotides, indicating it functions as negative regulator of TLR7 and TLR9 signaling cascades (PubMed:16735691, PubMed:19564354, PubMed:24586760). Down-regulates interferon production in response to interaction with BST2 on HIV-1 infected cells (PubMed:26172439). Activates a signaling cascade in complex with FCER1G that results in phosphorylation of Src family and Syk kinases and thereby triggers mobilization of intracellular Ca(2+) (PubMed:16735691, PubMed:19564354). Does not interfere with the differentiation of plasmacytoid dendritic cells into antigen-presenting cells (PubMed:24586760). Interacts with FCER1G; this stabilizes the expression of both proteins at the cell membrane (PubMed:16735691). Interacts with BST2; leads to activation of LILRA4-mediated signaling and down-regulation of the innate immune response to viral pathogens (PubMed:19564354, PubMed:26172439). Detected on plasmacytoid dendritic cells (at protein level). Detected on plasmacytoid dendritic cells, but not on monocytes or B cells.