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 a 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). {ECO:0000269|PubMed:16735691, ECO:0000269|PubMed:19564354, ECO:0000269|PubMed:24586760, ECO:0000269|PubMed:26172439}. This is the function of ENSG00000239961 (LILRA4, leukocyte immunoglobulin like receptor A4).