The M5 monoclonal antibody specifically binds to human CD126 which is also known as the alpha subunit of the human IL-6 Receptor (IL-6Rα). CD126 is an 80 kDa type I transmembrane glycoprotein, also known as gp80 and B cell stimulatory factor-2 (BSF-2) Receptor. The IL-6Rα subunit associates with the 130-160 kDa gp130 subunit (IL-6 Receptor β chain, CD130), that is shared with the receptor complexes for Leukemia Inhibitory Factor (LIF), Ciliary Neurotropic Factor (CNTF), Oncostatin M (OSM), IL-11, Cardiotropin 1 (CT-1) and possibly Neurotrophin-1/B Cell-Stimulating Factor 3 (NNT-1/BSF-3). The IL-6Rα chain binds IL-6 with low affinity; however the association with CD130 stabilizes the IL-6/IL-6Rα complex resulting in the formation of a high affinity ligand-receptor complex. The IL-6Rβ chain mediates signal transduction. CD126 is expressed at high levels by activated and EBV-transformed B cells, plasma cells and myeloma cells and at lower levels by most leucocytes, epithelial cells, fibroblasts, hepatocytes and neural cells. IL-6Rα exists in soluble form in human serum. The serum levels of soluble IL-6Rα appear to elevate in pathological situations such as multiple myeloma, Grave's disease, juvenile chronic arthritis and HIV. The M5 antibody is directed against an epitope not involved in interactions of CD126 with IL-6 or CD130.
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).