May function as an inhibitor of the B-cell receptor signaling. May function in the B-cell-mediated immune response. Interacts with PTPN6 and PTPN11. Specifically expressed by memory and monocytoid B-cells which populate spleen and lymph nodes. Preferentially expressed in memory B-cells associated with mucosal tissue (at protein level). Phosphorylated on cytoplasmic tyrosines upon activation. A chromosomal aberration involving FCRL4 is found in non-Hodgkin lymphoma (NHG). Translocation t(1;1)(p36.3; q21.1-2). A chromosomal aberration involving FCRL4 is found in multiple myeloma (MM). Translocation t(1;14)(q21;q32) that forms a FCRL4-IGHA1 fusion protein.