Biochemical identification of the antigen recognized by the monoclonal pan-B cell antibody Y29/55.

To examine the biochemical structure of the antigen recognized by the monoclonal pan-B cell antibody, Y29/55, the Daudi- and Jurkat-cell lines were labeled by two different methods and immunoprecipitation experiments were carried out. After surface labeling with iodine, two bands with molecular weights of about 38 and 42 kD were observed. The same two proteins were precipitated after biosynthetic labeling with (35S)-methionine from B cells and, to a lesser extent, from T cells. Therefore, it seems that the same proteins, or proteins with similar molecular weight, exist intracellularly in T cells as exist on the surface of, and possibly intracellularly, in B cells. It was confirmed that 80-90% of normal blood-derived B cells were stained with Y29/55 by indirect immunofluorescence. Double-labeling experiments with the pan-B cell antibodies Leu 16 (CD 20) and Leu 12 (CD 19) showed a B-cell population which could be stained with both antibodies (Y29/55 and Leu 16 or Y29/55 and Leu 12). A minor cell population was stained with the antibody Y29/55 alone. Our findings indicate that the antibody Y29/55 recognizes a B-cell antigen, which has not been described previously.