The M1/42 monoclonal antibody (mAb) specifically recognizes intact Histocompatibility-2 Region (H-2) class I antigens (Ags), also known as mouse Major Histocompatibility Complex class I (MHC-I) Ags. This mAb reportedly binds to one or more of the H-2 Ags (H-2K, H-2D, and likely H-2L) that are primarily expressed on most nucleated somatic cells of hematopoietic and nonhematopoietic origin. H-2 class I molecules are comprised of a ~45-50 kDa type I transmembrane heavy chain glycoprotein that is noncovalently linked to ~13 kDa β2-microglobulin (β2-m). The extracellular region of the polymorphic heavy chains is comprised of three globular domains (α1, α2, and α3), followed by a transmembrane region and a cytoplasmic tail. Sequence variations are manifest in regions of the α1 and α2 domains that line the peptide-binding cleft involved in Ag presentation. The M1/42 mAb reportedly binds to H-2 class I Ags from multiple mouse haplotypes including a, b, d, j, k, s, and u. It does not bind to separated H-2 class I heavy chains or β2-m. Cell surface CD8 molecules bind to invariant sites of the H-2 heavy chains and can provide coreceptor signaling for Ag-mediated activation through the T cell receptor. H-2 class I molecules that present self-Ags can lead to self-tolerance of maturing CD8+ T cells due to thymic selection. Alternatively, these molecules can present foreign peptide Ags to mature peripheral CD8+ T cells resulting in cell-mediated immune responses against foreign Ags. H-2 class I Ags also serve as ligands for activating and inhibitory receptors expressed by NK cells and some T cells. The M1/42 antibody is useful for analyzing H-2 class I Ag expression on cells or cell lines. Cells from different experimental systems, eg, stressed cells that have undergone infection or transformation, may express little or no H-2 class I Ag. In contrast, cells undergoing activation or responding to certain factors (eg, interferons) may express upregulated levels of these Ags.
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.