The AA4.1 monoclonal antibody specifically recognizes the Early B Lineage antigen which is also known as CD93, AA4 antigen, Ly-68, and Complement component C1q receptor (C1qRp). This 130-140-kDa type I transmembrane glycoprotein is expressed on immature B lymphocytes in the adult bone marrow and on hematopoietic progenitors and stem cells in adult bone marrow, fetal liver, and embryonic yolk sac. Although CD93+ cells are most plentiful in adult mouse bone marrow, a smaller number of CD93+ cells which express lower CD93 levels can be detected in the adult spleen using bright fluorescent conjugates of the AA4.1 antibody or an amplified indirect immunofluorescent staining procedure. It has been observed that the staining pattern of the 493 monoclonal antibody is similar to that of the AA4.1 antibody, in that both antibodies precipitate molecules of the same molecular weight. Staining with the AA4.1 antibody is not blocked by the 493 antibody. These results suggest that the antibodies recognize separate epitopes on the same Early B Lineage antigen.
The antibody was conjugated to BD Horizon™ BUV563 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 which has an Ex Max of 348 nm and an acceptor dye. The tandem has an Em Max at 563 nm. BD Horizon BUV563 can be excited by the 355 nm ultraviolet laser. On instruments with a 561 nm Yellow-Green laser, the recommended bandpass filter is 585/15 nm with a 535 nm long pass to minimize laser light leakage. When BD Horizon BUV563 is used with an instrument that does not have a 561 nm laser, a 560/40 nm filter with a 535 nm long pass may be more optimal. Due to the excitation and emission characteristics of the acceptor dye, there may be spillover into the PE and PE-CF594 detectors. However, the spillover can be corrected through compensation as with any other dye combination.