Abstract
IgE, the key molecule in atopy has been shown to bind two receptors,
FcRI, the high affinity receptor and FcεRII (CD23), mostly found on B
cells and that binds IgE with lower affinity. Whereas cross-linking of
IgE on FcRI triggers allergic reaction, binding of IgE to CD23 is known
to play an important role in both IgE synthesis and presentation. Thus,
targeting IgE-immune complexes on B cells has shown to enhance antibody
and T cell responses in mice and humans. However, the mechanisms that
regulate the targeting of the two receptors and the respective function
of the two pathways in inflammation or homeostasis are still matter of
debate. Here, we discuss several mechanisms related to IgE and IgE
binding to both receptors, as well as the influence of the antigen
binding on different immune cells expressing the receptors. One recent
paper has shown that free IgE preferentially binds to FcRI whereas IgE
immune complexes (IgE-ICs) are preferentially captured by CD23. Binding
of IgE-ICs to CD23 on B cells can on one hand regulate serum IgE and
prevent effector cell activation and on the other hand facilitate the
antigen presentation by delivering antigen to dendritic cells. The data
suggest that CD23 play a multifunctional role in regulating the allergic
response pathway.