New concepts of IgE regulation

B cell switch to IgE expression is mediated by IL-4 and is regarded as a T helper cell-related phenomenon. In this overview we describe that IgE switch can also be induced by mast cell/basophil like cells (from splenic non-B, non-T cells), activated by IgE receptor cross-linking and/or IL-3 which results in IL-4 production by these cells. Furthermore, activated mast cells produce their own growth factors, IL-3 and GM-CSF. Thus, activation of mast cells can provoke an ongoing local allergic reaction as long as antigen confrontation is maintained, a process which is sustained by further IgE production as well as renewal of mast cells. It is furthermore demonstrated that in certain established immune situations the IgE response may become independent of IL-4, namely in the spontaneous in vitro IgE expression of cells from atopic individuals as well as in an in vitro antigen-induced secondary IgE response of spleen cells derived from previously immunized mice. Thus, IgE-switched B cells may persist in vivo and may represent a pool of potentially IgE-producing cells. Finally, a selective inhibition of the IgE response is described in vitro and in vivo by the use of so-called non-anaphylactic monoclonal anti-IgE antibodies. Such antibodies bind to surface IgE+ B cells, but not to IgE-sensitized mast cells, and thereby inhibit IgE responses. Non-anaphylactic antibodies blocked the binding of allergen-specific IgE to mast cells by competing with the Fc epsilon on these cells. As a consequence they do not induce but rather prevent allergen-induced mediator release by mast cells.(ABSTRACT TRUNCATED AT 250 WORDS)