INTACT, 45-KDA (MEMBRANE) FORM OF CD23 IS CONSISTENTLY MITOGENIC FOR NORMAL AND TRANSFORMED B-LYMPHOBLASTS

When isolated from lysates of the RPMI 8866 B lymphoblastoid cell line, the CD23 antigen was found to be present be in two forms corresponding to the intact 45‐kDa membrane species and to a 25‐kDa product that is more usually found as a released fragment in the extracellular medium. By contrast with preparations of extracellular species of CD23 which were seen to be variable in their biological activity, cell‐associated CD23 was consistently mitogenic both for autogenous transformed B lymphoblasts and for pre‐activated normal B cells. Addition to the normal cocktail of protease inhibitors of Nα‐tosyl‐L‐lysine chloromethylketone (TLCK), which has selectivity for trypsin‐like serine proteases, resulted in preparations of CD23 from RPMI 8866 cell lysates that were exclusively in the 45‐kDa intact form; such material retained full and reliable activity in the biological assays. The implications of these observations for the autocrine control of B lymphocyte growth are discussed. Copyright © 1990 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim