Down regulation in B lymphocytes: low dose signals

Picogram quantities of dinitrophenylated (DNP) dextran, a thymus‐inde‐pendent antigen or lipopolysaccharide, a B cell mitogen, signal down B lymphocytes to unresponsiveness. Down signals were detected by a decision test in which signaled lymphocytes were allowed one hour to react to an immunogenic pulse of DNP‐dextran. Depletion of T cells or macrophages did not interfere with the generation of down signals. The signaling can proceed entirely at 4 °C and its negative effect is transitory. Down signals which could be detected after 15 min at 37°C were reversed by 60 min. It is suggested that down regulation by low dose antigenic signals provides a means of distinguishing background noise from true antigenic stimuli.