The In-1 monoclonal antibody specifically binds to CD74, the MHC class II-associated Invariant chain (Ii), expressed in I-A+ cell populations. Although it is predominantly expressed intracellularly, it has also been detected on the cell surface of some B-cell lines and at low levels on a small number of B lymphocytes. In the mouse, alternatively spliced transcripts encode 31-kDa and 41-kDa isoforms, and the cell-surface CD74 has a chondroitin sulfate side chain which allows it to interact with CD44. CD74 is directly involved in the intracellular transport of MHC class II molecules and antigen presentation, and it affects the maturation of T and B lymphocytes.
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.