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™ BV510 which is part of the BD Horizon Brilliant™ Violet family of dyes. With an Ex Max of 405-nm and Em Max at 510-nm, BD Horizon BV510 can be excited by the violet laser and detected in the BD Horizon V500 (525/50-nm) filter set. BD Horizon BV510 conjugates are useful for the detection of dim markers off the violet laser.