Human IgE Fc-receptors and their soluble isoforms.
The high affinity IgE Fc receptor, Fc-epsilon-RI (FcεRI), has two transmembrane isoforms, FcεRIαβγ2 and FcεRIαγ2. The soluble isoform, sFcεRI, is a single chain receptor consisting of a truncated version of the IgE-binding FcεRIα subunit. Several different soluble isoforms of the transmembrane low affinity IgE Fc receptor, FcεRII or CD23, have been described. A detailed summary of soluble CD23 (sCD23) isoforms and their cleavage sites is provided in Table 2. Galectin-3 is a secretory IgE Fc receptor. After secretion, galectin-3 can attach to cell membranes via interacting with a large number of carbohydrate structures displayed by cell surface proteins. Additionally, an intracellular pool of galectin-3 can be found in the cytoplasm and the nucleus.