Functions of interleukin-4 on human B lymphocytes

In vitro studies have demonstrated that IL-4 can either enhance or inhibit the proliferation of human B cells depending on their mode of activation and the nature of the calls and/or cytokines in the immediate environment. Of these in vitro effects, it is now clear from in vivo studies in mice, that IL-4 plays a key role in the production of IgE [15]. It is, however, not yet determined whether IL-4 plays any role in vivo in the antigen-dependent clonal expansion of B cells. Our demonstration of the crucial role of cross-linking of the CD40 antigen in the proliferation and differentiation of human B lymphocytes leads us to question the role of this antigen. Recent studies have demonstrated this antigen to be homologous to the nerve growth factor receptor [16] and the two receptors for TNF [17–19]. It is therefore tempting to speculate that the CD40 antigen may either be the receptor for a cytokine or the ligand for a membrane counterstructure expressed on cells interacting with B cells.