To E or not to E? Can and IL-4-induced B cell choose between IgE and IgG4?

Parasite immunologists had known for some time that IgE-mediated hypersensitivity reactions are rare in patients with chronic helminth infections, even though basophils and mast cells in these patients are sensitized with antiparasite IgE and exposed, often continuously, to parasite antigens. The inhibition of allergic reactivity in chronic helminth infections is mainly due to IgG4 'blocking antibodies' in the serum of the infected individual. IgG4 do not fix complement and bind weakly to Fc gamma receptors. Thus, antigen binding by IgG4, unlike IgE, is likely to have no or minimally harmful consequences. The discovery that, similar to IgE, expression of IgG4 is IL-4-dependent and is an intermediate step in sequential switching from IgM to IgE makes it imperative to understand how the two isotypes are coregulated and whether the two responses can be uncoupled, selectively boosting IgG4 over IgE. The ultimate goal is to apply to allergy the lesson we learnt from helminth infections.