Human interleukin-2 promotes proliferation of activated B cells via surface receptors similar to those of activated T cells

Human interleukin-2 (IL-2) is a glycoprotein of relative molecular mass (Mr) 15,000, which is released by T lymphocytes on stimulation with antigen or mitogen and functions as a T-cell growth factor (TCGF) by inducing proliferation of activated T cells1. It is generally accepted that resting or activated T cells do not respond directly to IL-2 but require for their proliferation other T-cell-derived lymphokines usually referred to as B-cell growth factors (BCGFs)2,3. Recently, however, a monoclonal antibody reacting with the IL-2 receptor molecules expressed by activated T cells (anti-Tac)4,5was shown to react also with certain B tumour cells6; in addition, murine B cells proliferate in response to pure human IL-27. We now show that recombinant IL-2, derived from Escherichia coli expressing the human gene8, is able to promote strong proliferation of human B cells activated with protein-A-rich Staphylococcus aureus Cowans strain I2. Moreover, we demonstrate that the anti-Tac antibody also reacts with S. aureas-activated normal B cells and inhibits sharply the proliferative response of such cells to IL-2. Finally, immunoprecipitation experiments reveal that anti-Tac defines similar molecules on activated T and B cells.