The MAR-1 monoclonal antibody specifically recognizes Fc-epsilon RI-alpha (FceR1 alpha, also known as FcεR1α or FcER1a) which is likewise known as the IgE Fc receptor subunit alpha. FcεR1α is a type I transmembrane glycoprotein that is encoded by Fcer1a (Fc receptor, IgE, high affinity I, alpha polypeptide) which belongs to the Ig gene superfamily. As a single IgE-binding alpha subunit, FcεR1α complexes with signal transducing subunits including one beta subunit (FcεRIβ encoded by Ms4a2) and two disulfide-linked gamma subunits (FcεRIγ encoded by Fcer1g) to form the high-affinity receptor for IgE, Fc epsilon RI (FcεR1 or FcER1). FcεR1 is expressed on basophils and mast cells. Binding of cognate antigens (allergens) to FcεR1 with bound IgE antibodies leads to cellular activation and the release of mediators, including histamine and cytokines, that are responsible for allergic reactions. Tang et al. (2019) have reported that the MAR-1 antibody crossreacts with two other mouse Fc receptor chains, FcγRI (CD64) and FcγRIV (CD16-2), that are expressed by monocytes, macrophages, dendritic cells, or neutrophils. They suggested MAR-1 binding is specific for FcεRIa only on mast cells and basophils and that for other cell types reactive with the MAR-1 antibody, it may be appropriate to refer to these as MAR-1-positive (MAR-1+) cells.
The antibody was conjugated to BD Horizon™ BV650 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 650-nm. BD Horizon BV650 can be excited by the violet laser and detected in a filter used to detect APC-like dyes (eg, 660/20-nm filter). Due to the excitation and emission characteristics of the acceptor dye, there will be spillover into the APC and Alexa Fluor® 700 detectors. However, the spillover can be corrected through compensation as with any other dye combination.