The OKT4 monoclonal antibody specifically recognizes CD4 which is also known as T4 and Leu-3. CD4 is expressed on most thymocytes, T-helper/inducer cells, regulatory T cells (Tregs), and NKT cells. It is also variably expressed on monocytes, macrophages, and some dendritic cells. CD4 is a ~55 kDa type I transmembrane glycoprotein that is encoded by CD4 which belongs to the immunoglobulin superfamily (IgSF). CD4 binds to a nonpolymorphic region of MHC class II and serves as a coreceptor, along with the T cell receptor for antigen (TCR), for the MHC Class II-restricted recognition of antigens on antigen-presenting cells. CD4 also functions as a receptor for human immunodeficiency viruses (HIV). CD4 has four immunoglobulin-like extracellular domains in its extracellular region and a CXCP binding motif for p56Lck in its cytoplasmic domain which regulates the antigen-bound TCR-induced signaling cascade.
The antibody was conjugated to BD Horizon BV480 which is part of the BD Horizon Brilliant™ Violet family of dyes. With an Ex Max of 436-nm and Em Max at 478-nm, BD Horizon BV480 can be excited by the violet laser and detected in the BD Horizon BV510 (525/40-nm) filter set. BV480 has less spillover into the BV605 detector and, in general, is brighter than BV510.