FUNCTION OF B-CELL ANTIGEN RECEPTOR OF DIFFERENT CLASSES

Most mature B lymphocytes co-express two classes of antigen receptor, IgM and IgD. The differences in the signal transduction from the 2 rec eptors are still a matter of controversy. We have analysed B-cell line s expressing IgM or IgD antigen receptors with the same antigen specif icity. Cross-linking of these receptors with either antigen or class-s pecific antibodies results in the activation of protein tyrosine kinas es and the phosphorylation of the same substrate proteins. The kinetic s and intensity of phosphorylation, however, were quite different betw een the 2 receptors when they were cross-linked by antigen. In membran e IgM-expressing cells, the substrate phosphorylation reached a maximu m already after 1 min and diminished after 60 min whereas in the membr ane IgD-expressing cells, the substrate phosphorylation increases furt her over time, reached its maximum at 60 min and persisted longer than 240 min after exposure to antigen. Recently prolonged signaling has b een found to be responsible for signaling differences between tyrosine kinase receptors using otherwise similar signaling routes. Thus, the duration of a signal may be an important biological feature of signal transducing cascades.