The R139 monoclonal antibody specifically binds to CD93 which is also known as Complement component C1q receptor (C1qR), C1q receptor 1 (C1qR1), or Matrix-remodeling-associated protein 4 (MXRA4). The immunogen used to generate the R139 hybridoma was a preparation of CD93 protein. Human CD93 is a transmembrane glycoprotein that is highly expressed on monocytes, macrophages, granulocytes, and endothelial cells but not on T and B lymphocytes. CD93 is also known as the C1q/MBL/SPA Receptor as it binds C1q, the recognition subunit of the first component (C1) of the complement pathway, as well as MBL (Mannose-binding-lectin) and SPA (Pulmonary Surfactant Protein A). Human C1qRp is involved in the C1q-mediated enhancement of phagocytosis. R139 is suitable to detect CD93 expression on cells of myeloid lineage by flow cytometry, and CD93 in cellular lysates by Western blotting or immunoprecipitation. In addition, R139 reportedly neutralizes C1q-mediated enhancement of phagocytosis. CD93 has also been reported to define a human stem cell population with hematopoietic and hepatic potential.
The antibody was conjugated to BD Horizon™ BUV805 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 805 nm. BD Horizon Brilliant BUV805 can be excited by the ultraviolet laser (355 nm) and detected with a 820/60 filter and a 770LP.