Editing Mast cell (section)

===Structure of the high-affinity IgE receptor, FcεR1===
[[FCER1|FcεR1]] is a high affinity IgE-receptor that is expressed on the surface of the mast cell. FcεR1 is a tetramer made of one alpha (α) chain, one beta (β) chain, and two identical, disulfide-linked gamma (γ) chains. The binding site for [[IgE]] is formed by the extracellular portion of the α chain that contains two domains that are similar to Ig. One transmembrane domain contains an [[aspartic acid]] residue, and one contains a short cytoplasmic tail.<ref name=pmid10358778>{{cite journal |author=Kinet JP |title=The high-affinity IgE receptor (FcεRI): from physiology to pathology |journal=Annual Review of Immunology |volume=17 |pages=931–72 |year=1999 |pmid=10358778 |doi=10.1146/annurev.immunol.17.1.931}}</ref> The β chain contains, a single immunoreceptor tyrosine-based activation motif [[Immunoreceptor tyrosine-based activation motif|ITAM]], in the cytoplasmic region. Each γ chain has one [[Immunoreceptor tyrosine-based activation motif|ITAM]] on the cytoplasmic region. The signaling cascade from the receptor is initiated when the ITAMs of the β and γ chains are phosphorylated by a tyrosine kinase. This signal is required for the activation of mast cells.<ref name="Role of Mast Cells">{{cite book |first1=Abul K. |last1=Abbas |first2=Andrew H. H. |last2=Lichtman |first3=Shiv |last3=Pillai | name-list-style = vanc |year=2011 |title=Cellular and Molecular Immunology |edition=7th |location=New York, NY |publisher=Elsevier |chapter=Role of Mast Cells, Basophils and Eosinophils in Immediate Hypersensitivity |chapter-url=https://www.inkling.com/read/cellular-and-molecular-immunology-abbas-7th/chapter-19/role-of-mast-cells-basophils |isbn=978-1-4377-1528-6}}{{page needed|date=April 2014}}</ref> Type 2 helper T cells,([[Th2]]) and many other cell types lack the β chain, so signaling is mediated only by the γ chain. This is due to the α chain containing endoplasmic reticulum retention signals that causes the α-chains to remain degraded in the ER. The assembly of the α chain with the co-transfected β and γ chains mask the ER retention and allows the α β γ complex to be exported to the golgi apparatus to the plasma membrane in rats. In humans, only the γ complex is needed to counterbalance the α chain ER retention.<ref name=pmid10358778/>