The role of non-antigen receptors in mast cell signalling processes.

Cytophilic antibodies of the IgE class play two distinctive roles in the immunological triggering of mast cell, initially by binding to Fc receptors on the plasma membrane and secondly, by transmitting to the sensitised target cell the effects of their subsequent interaction with specific antigen (allergen). In contrast to the claim that the IgE antibody merely acts as a surrogate receptor in its latter role, evidence is presented in support of the contention that it is actively involved in mast cell triggering by providing a signal to a second "receptor" [i.e. other than Fc(epsilon)R]. Synthetic peptide studies have provided an insight into the structural characteristics of such an Fc effector site, besides beginning to suggest the manner of its interaction with the mast cell membrane. In discussing the implication of our findings, this type of immunological trigger process is contrasted with that brought about by hormone agonists. It is suggested that the cytophilic IgE antibody can be regarded as a pro-hormone, which only gains hormonal status as a result of cross-linking by specific antigen.