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™ BUV496 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 with an Ex Max of 348-nm and an acceptor dye with an Em Max at 496-nm. BD Horizon BUV496 can be excited by the ultraviolet laser (355 nm) and detected with a 515/30 nm filter with a 450LP. Due to the excitation of the acceptor dye by other laser lines, there may be significant spillover into the channel detecting BD Horizon V500 or BV510 (eg, 525/40-nm filter). However, the spillover can be corrected through compensation as with any other dye combination.