B-lymphocyte-specific membrane protein that plays a role in the regulation of cellular calcium influx necessary for the development, differentiation, and activation of B-lymphocytes (PubMed:12920111, PubMed:3925015, PubMed:7684739). Functions as a store-operated calcium (SOC) channel component promoting calcium influx after activation by the B-cell receptor/BCR (PubMed:12920111, PubMed:18474602, PubMed:7684739). {ECO:0000269|PubMed:12920111, ECO:0000269|PubMed:18474602, ECO:0000269|PubMed:3925015, ECO:0000269|PubMed:7684739}. This is the function of MS4A1 (membrane spanning 4-domains A1, ENSG00000156738).