Loss of surface IgD by human B lymphocytes during polyclonal activation*

Surface and cytoplasmic immunoglobulins were studied by direct immunofluorescence in pokeweed mitogen-stimulated cultures of human blood lymphocytes. The results compared to those of studies of unstimulated cultures and of fresh normal lymphocytes showed a striking decrease in surface IgD during terminal maturation of B lymphocytes into plasma cells. The number of cells which expressed IgG Fe receptor also decreased, although to a lesser extent.