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Different Stabilities of the Structurally Related Receptors for IgE and IgG on the Cell Surface Are Determined by Length of the Stalk Region in Their -Chains¹

Department of Immune Regulation, Tokyo Medical and Dental University Graduate School, Tokyo, Japan

A variant of the high affinity IgE receptor FcRI, which is composed of - and -chains without the -chain, is expressed on human APC, such as dendritic cells, and has been suggested to facilitate Ag uptake through IgE and hence to facilitate Ag presentation to T cells. The level of FcRI on these cells is correlated with the serum IgE concentration, suggesting IgE mediates the up-regulation of the 2-type FcRI. The IgE-mediated FcRI up-regulation on mast cells and basophils has been shown to enhance the ability of these cells to release chemical mediators and cytokines that are responsible for allergic inflammatory reactions. Here, to elucidate the mechanism controlling FcRI expression, we compared two structurally related Ig receptors, human FcRI and FcRIIIA, which carry different -chains but the same -chains. The half-life of FcRI on the cell surface was short unless it bound IgE, whereas FcRIIIA was stably expressed without IgG binding. Shuffling of the non Ig-binding portions of the FcRI and FcRIIIA chains revealed that the stalk region was critical in determining the difference in their stability and ligand-induced up-regulation. Unexpectedly, analyses with added or deleted amino acids in the stalk region strongly suggested that the length rather than the amino acid sequence of the stalk region was of major importance in determining the different stabilities of FcRI and FcRIIIA on the cell surface. This finding provides new insights into the mechanism regulating surface FcRI expression.

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The JI 2006 176: 6365-6366. [Full Text]  

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