The L120 monoclonal antibody specifically recognizes CD4. CD4 is an ~59 kDa type I transmembrane glycoprotein that belongs to the Ig gene superfamily. CD4 is expressed on helper-inducer subset of T lymphocytes and monocytes. The CD4 antigen is involved in the Major Histocompatibility Complex (MHC) class II-restricted recognition of foreign antigens and has been identified as a receptor for HIV. The L120 antibody recognizes amino acids 306-370 of the antigen and does not block the binding of the gp120 of HIV, but inhibits the proliferation of CD4 T lymphocytes to MHC class II antigens. The CD4 antigen is present on most thymocytes, approximately 40% of peripheral blood lymphocytes, and at lower density on monocytes. Peripheral blood CD4+ T lymphocytes are lost over time during HIV infection, and this loss is correlated with disease progression.
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.