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™ BUV661 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 661-nm. BD Horizon Brilliant BUV661 can be excited by the ultraviolet laser (355 nm) and detected with a 670/25 filter and a 630 nm LP. Due to cross laser excitation of this dye, there may be significant spillover into channels detecting APC-like emissions (eg, 670/25-nm filter).
Due to spectral differences between labeled cells and beads, using BD™ CompBeads can result in incorrect spillover values when used with BD Horizon BUV661 reagents. Therefore, the use of BD CompBeads or BD CompBeads Plus to determine spillover values for these reagents is not recommended. Different BUV661 reagents (eg, CD4 vs. CD45) can have slightly different fluorescence spillover therefore, it may also be necessary to use clone-specific compensation controls when using these reagents.