The 509F6 monoclonal antibody specifically binds to Fc receptor-like 5 (FCLR5), a type I transmembrane glycoprotein that is also known as CD307e, FCRH5 (Fc receptor homolog 5) and IRTA2 (immunoglobulin superfamily receptor translocation associated 2). FCRL5 (CD307e) is a member of the Immunoglobulin (Ig) gene superfamily with 9 extracellular Ig domains, an intracellular immunoreceptor tyrosine-based activating motif (ITAM)-like sequence and two intracellular immunoreceptor tyrosine-based inhibitory motif (ITIM)-like sequences. Like other Fc receptor-like proteins, FCRL5 (CD307e) is homologous to FcγR1 (CD64) and binds to immunoglobulins, specifically the IgG isotypes, and it may play a role in the regulatory interactions of immune complexes with B lymphocytes. FCRL5 (CD307e) is differentially expressed in the B cell lineage, with little expression on peripheral blood cells and upregulated expression on plasma cells and some leukemias and lymphomas. mAb 509F6 binds to an epitope within the first 3 Ig domains of FCRL5 and blocks FCRL5's interaction with immune complexes.
The antibody was conjugated to BD Horizon™ BUV563 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 which has an Ex Max of 348 nm and an acceptor dye. The tandem has an Em Max at 563 nm. BD Horizon BUV563 can be excited by the 355 nm ultraviolet laser. On instruments with a 561 nm Yellow-Green laser, the recommended bandpass filter is 585/15 nm with a 535 nm long pass to minimize laser light leakage. When BD Horizon BUV563 is used with an instrument that does not have a 561 nm laser, a 560/40 nm filter with a 535 nm long pass may be more optimal. Due to the excitation and emission characteristics of the acceptor dye, there may be spillover into the PE and PE-CF594 detectors. However, the spillover can be corrected through compensation as with any other dye combination.