Regulation of allergy by Fc receptors

The aggregation of high-affinity IgE receptors (Fc RI) on mast cells and basophils has long been known as the critical event that initiates allergic reactions. Monomeric IgE was recently found to induce a variety of effects when binding to Fc RI. Upregulation of Fc RI only requires binding, whereas other responses require Fc RI aggregation. Interestingly, Fc RI aggregation has recently been understood to generate a mixture of positive and negative intracellular signals. Mast cells and basophils also express low-affinity and, under specific conditions, high-affinity IgG receptors. When co-engaging these receptors with Fc RI, IgG antibodies can amplify or dampen IgE-induced mast cell activation. On the basis of these findings, it has been proposed that FcRs can be used as targets and/or tools for new therapeutic approaches to allergies.