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 BUV615 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome with an Ex Max near 350 nm and an Em Max near 615 nm. BD Horizon Brilliant BUV615 can be excited by the ultraviolet laser (355 nm) and detected with a 610/20 filter and a 595 nm LP. Due to the excitation of the acceptor dye by the blue/yellow-green laser line, there may be significant spillover into channels detecting PE-CF594 like emissions (eg, 610/20-nm filter).