CD244 (also known as 2B4 Antigen) is a member of the CD2 subset of the immunoglobulin superfamily (CD2 IgSF). It is expressed on all natural killer (NK) cells, IL-2–activated NK cells (LAK), and a subset of T lymphocytes which mediate non-MHC–restricted cytotoxicity. The C9.1 antibody specifically recognizes CD244.1, the 2B4 alloantigen which is expressed by certain cells in most strains tested (A/J, AKR/N, BALB/c, CBA/N, C3H/He, DBA/1, DBA/2, NZB/N, SJL/J, 129/Svj), but not by cells from C57BL/6 or C58/J mice. The expression of the CD244.1 alloantigen on B lymphocytes that was originally described, has not been confirmed in later studies. The extracellular domain of CD244 is a ligand for another CD2 IgSF member, CD48.
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.