Antibodies directed against the alpha chain (30 kDa; chromosome 1q23.2) of the high-affinity IgE receptor (Fc epsilon RI alpha) expressed on dermal mast cells and basophilic leukocytes. The IgE receptors consist of a complex of a gamma 1, gamma 2 , alpha and beta chain. The alpha chain contains two domains alpha 1 and alpha 2 . In about 25 % of cases, the antibodies are directed against the IgE binding site of the receptor. In the remaining 75 %, the antibodies react with epitopes located outside the IgE binding site.
Histamine release by the autoantibodies occurs after cross-linking of adjacent receptors by the antibodies bound to the alpha chain. After cross-linking of the receptor, intracellular activation of the protein thyrosine kinase LYN and DYC by the gamma 1 and gamma 2 chains occurs, which in turn activate protein kinase C and initiate the elimination of histamine. Whether the antibodies trigger an activation of the complement system is still debatable.