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 (Hannah.gould@kcl.ac.uk)

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, C, C, C1-4, and C1 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,

FcRI (left), and the “low-affinity” IgE receptor, CD23, also known as FcRII

(right). The plasma membrane is grey and intracellular cytoplasmic

sequences of the two -chains, the -chain, and the -chain are shown from

left to right in the cytoplasm. The -chain with two extracellular Ig-like

domains (blue) contains the extracellular IgE binding sites. The - and -

chains play important roles in signal transduction [1]. CD23 (or FcRII) 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 FcRI) 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 FcRI 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 -chain of IgM is

shown at the top (yellow) along with the 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 -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].

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