The OX-38 antibody specifically recognizes the CD4 antigen on most thymocytes, a subpopulation of mature T lymphocytes (ie, MHC class II-restricted T cells, including most T helper cells), monocytes, macrophages, and some dendritic cells. CD4 is an antigen coreceptor on the T-cell surface which interacts with MHC class II molecules on antigen-presenting cells. It participates in T-cell activation through its association with the T-cell receptor complex and protein tyrosine kinase lck. The OX-38 antibody has been reported to bind to the same epitope of CD4 as that recognized by W3/25 mAb, which is a different epitope than that recognized by OX-35 mAb. In vivo blocking of some cell-mediated immune responses by mAb OX-38 has been reported. Injection of OX-38 mAb induces allograft unresponsiveness in rats, with varying results depending on the rat strain used (high or low responder). Furthermore, in vivo depletion of CD4+ lymphocytes has been reported with this antibody.
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).