Supplementary Material
IgE Responses in Mouse and Man and the Persistence of IgE Memory
Hannah J Gould and Faruk Ramadani
Divisions of Cell & Molecular Biophysics and Asthma, Allergy and Lung Biology, King’s College London, London SE1 1UL, UK
Corresponding author: Gould HJ ()
Supplementary Fig. 1 Antibody classes, IgE receptors and the function of IgE
A) Antibody classes in the human immune system
Above: The five antibody classes, (IgM, IgD, IgG, IgA and IgE, color coded), but not the four subclasses of IgG, IgG1, IgG2, IgG3 and IgG4, and two of IgA, A1 and A2, are shown. All nine isotypes differ in their heavy-chain constant (C) regions, Cm, Cd, Cg1-4, and Ca1 and 2. The heavy- and light-chains and two heavy-chains are covalently linked (only single disulphide bonds are shown for simplicity). The variable region containing the antigen binding site (white) is unchanged after CSR (see Supplementary Fig. 2), while the different constant regions provide limited functional diversity.
Below: All nine different constant regions are encoded in a tandem array on human chromosome 14.
(B) IgE cell receptors
Schematic illustration of the two IgE receptors, the “high-affinity” receptor, FceRI (left), and the “low-affinity” IgE receptor, CD23, also known as FceRII (right). The plasma membrane is grey and intracellular cytoplasmic sequences of the two g-chains, the b-chain, and the a-chain are shown from left to right in the cytoplasm. The a-chain with two extracellular Ig-like domains (blue) contains the extracellular IgE binding sites. The g- and b-chains play important roles in signal transduction [1]. CD23 (or FceRII) is a C-type lectin protein (C-terminal extracellular and N-terminal cytoplasmic sequence) It is a homopolymer containing three identical polypeptide chains. There are three IgE binding sites in the lectin domains (yellow) are connected to the membrane and cytoplasmic sequence by a coiled-coil stalk [2].
(C) The function of IgE in the characteristic immediate hypersensitivity reactions.
IgE binds to FceRI) on mast cells to sensitize the cells for allergen activation, then multivalent allergens cross-link the allergen-IgE complexes to trigger cell activation. Substances released by the activated mast cells induce the symptoms of allergy. Allergic reactions occur rapidly (within minutes) relative to IgG or IgA immune reactions, because IgE antibodies are constantly secreted by IgE+ PCs in the bone marrow and tighly sequestered by FceRI on the mast cells in the target organs of allergy. Hypersensitivity reflects the low number of crosslinks required to fire off the cells [2, 3].
Supplementary Figure 2. The process of class switch recombination to IgE
The general process of CSR is exemplified by direct CSR from IgM to IgE in the human Ig heavy-chain locus. The gene expressing the m-chain of IgM is shown at the top (yellow) along with the e germline gene (green). The important genetic elements shown comprise the expressed variable (VDJ) region, the transcriptional enhancer (E), the ”intervening” exons (I) and switch (S) regions linked to the various constant (C)-region coding sequences. The principal events in CSR are shown underneath. The synthesis of a germline gene transcript, induced by IL-4 (or IL-13), precedes CSR and is required in the mechanism of recombination [4, 5]. AID), which induces DNA breakage in the two Switch (S) regions to be recombined [6]. After CSR a new germline gene, referred to as a “post-switch (germline) transcript” in this review, is synthesized. Recombination involves looping out and deleting the intervening sequence between the break points in the two S regions. The ends of the deleted sequence are joined to form a circle. Transcription in the circle continues from the I region promoter, previously linked to the newly expressed constant region gene and now linked through a hybrid switch junction (green/yellow circle) to the previously expressed constant-region gene. The broken ends of the two switch regions in the shortened chromosome are joined to express the new heavy-chain isotype with no change in antigen specificity determined by the variable region (white rectangles). Transcription starts at the VDJ promoter and continues through the hybrid switch junction (yellow/green) and produces e-chain mRNA after splicing of the precursor and translation of the mRNA into protein. Sequences of the hybrid switch junctions are useful in revealing the genes that have undergone CSR [7-9].
References
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