The OKT3 monoclonal antibody specifically recognizes the CD3 epsilon subunit (CD3e/CD3ε) of the CD3 complex which consists of four transmembrane proteins (γ, δ, ε, ζ) that are associated with the T cell antigen receptor (TCR) to form the CD3/TCR complex. The CD3 complex associates with either TCR αβ or TCR γδ heterodimers that are alternatively expressed by some thymocytes, T cells or NKT cells. The CD3 complex is required for the cell surface expression and signal-transducing functions of the TCR. The CD3 complex is expressed by ~60-85% thymocytes and by all peripheral mature T cells. CD3e is also known as T3E or TCRE. CD3e is a ~20 kDa unglycosylated type I transmembrane protein that is encoded by CD3E which belongs to the immunoglobulin superfamily (IgSF). CD3e has an Ig-like extracellular domain (ECD) and an immunoreceptor tyrosine-based activation motif (ITAM) in its cytoplasmic domain. The OKT3 antibody can reportedly fix complement, stimulate T cell proliferation and cytokine production, and block the binding of other human CD3e-specific antibodies including UCHT1 and SK7.
The antibody was conjugated to BD Horizon BV750 which is part of the BD Horizon Brilliant™ Violet family of dyes. This dye is a tandem fluorochrome of BD Horizon BV421 with an Ex Max of 405-nm and an acceptor dye with an Em Max at 750-nm. BD Horizon Brilliant BV750 can be excited by the violet laser (405 nm) and detected with a 750/30 nm filter with a 740 nm long pass. Due to spectral differences between labeled cells and beads, using BD™ CompBeads can result in incorrect spillover values when used with BD Horizon BV750 reagents. Therefore, the use of BD CompBeads or BD CompBeads Plus to determine spillover values for these reagents is not recommended.