The HMPV monoclonal antibody specifically binds to CD227 which is also known as Mucin-1 (MUC1). A major form of CD227 is expressed as a type I transmembrane glycoprotein. CD227 belongs to the epithelial mucin family whose members are heavily O-glycosylated and characterized by high molecular weight, and an amino acid composition rich in serine, threonine, proline, and glycine. CD227 is variably expressed on the surfaces of normal and malignant glandular and ductal epithelial cells, and some hematopoietic cell lineages including subsets of T cells, B cells, monocytes and dendritic cells. Soluble forms of CD227 may arise by shedding from the cell surface or by secretion of forms derived from alternative RNA splicing. The HMPV antibody binds to the core peptide of the MUC1 protein. The core protein contains a domain of 20 amino-acid tandem repeats which function as multiple epitopes for this monoclonal antibody. Incomplete glycosylation of some tumor-associated mucins may lead to variable unmasking of the multiple peptide epitopes leading to the observed differences in immunostaining intensities between cells from normal and malignant tissues. CD227 plays roles in the provision of protective barrier function, the regulation of cellular adhesion, and the transduction of multiple signal pathways.
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).
Due to spectral differences between labeled cells and beads, using BD™ CompBeads can result in incorrect spillover values when used with BD Horizon BUV661 reagents. Therefore, the use of BD CompBeads or BD CompBeads Plus to determine spillover values for these reagents is not recommended. Different BUV661 reagents (eg, CD4 vs. CD45) can have slightly different fluorescence spillover therefore, it may also be necessary to use clone-specific compensation controls when using these reagents.