The 493 antibody reacts with a cell-surface protein of 130-140 kDa expressed on immature B lymphocytes and a small fraction of newly formed B cells, but not on mature B lymphocytes. The antigen's distribution was defined through the use of antibodies to CD24 (Heat Stable Antigen), IgM, IgD, and CD45R/B220, which are commonly used to discriminate B-cell maturation stages. 493 mAb reacts with the majority of B220+ cells in bone marrow and a fraction of B220+ B cells in spleen, which are CD24[high], IgM[high], and IgD[low]. Cells binding 493 mAb were not detected in thymus, lymph nodes, or peritoneal cavity. This result suggested that 493 mAb does not stain B-1 B cells (CD5+ B lymphocytes), which are particularly found in the peritoneal cavity. The 493 mAb does not seem to have any biological effect when incubated with immature B lymphocytes. It has been observed that the staining pattern of mAb 493 is similar to that of mAb AA4.1, that both antibodies precipitate molecules of the same molecular weight, and that staining by mAb AA4.1 is not blocked by mAb 493, suggesting that the antibodies recognize separate epitopes of the same Early B Lineage antigen.
The antibody was conjugated to BD Horizon BUV615 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome with an Ex Max near 350 nm and an Em Max near 615 nm. BD Horizon Brilliant BUV615 can be excited by the ultraviolet laser (355 nm) and detected with a 610/20 filter and a 595 nm LP. Due to the excitation of the acceptor dye by the blue/yellow-green laser line, there may be significant spillover into channels detecting PE-CF594 like emissions (eg, 610/20-nm filter).