Allergic Reactivity and Memory Occur Independently of Sequential Switching Through IgG1

Allergic reactions to foods are primarily driven by allergen-binding immunoglobulin (Ig)E antibodies. IgE-expressing cells can be generated through direct switching from IgM to IgE or a sequential class switching pathway where activated B cells first switch to an intermediary isotype, most frequently IgG1, and then to IgE. It has been proposed that sequential class switch recombination is involved in augmenting the severity of allergic reactions, generating high affinity IgE, differentiation of IgE plasma cells, and in holding the memory of IgE responses. We directly tested these possibilities by comparing the allergic immunity of wild-type and IgG1-deficient (hMT) mice. We found that sequential switching through IgG1 was not required to maintain the binding capacity of IgE nor for its ability to promote degranulation and elicit anaphylaxis against bona fide food allergens. Furthermore, the absence of sequential switching modestly impacted IgE affinity and clinical reactivity against hapten antigens, suggesting that the nature of the antigen impacts the requirement for sequential switching. At a cellular level, the capacity to undergo sequential switching through IgG1 provided no competitive advantage for subsequent IgE expression among germinal center B cells or plasma cells. Furthermore, the recall of allergic immunity at memory timepoints was preserved in the absence of sequential switching through IgG1, a finding that corresponded with intact type 2 memory B cell polarization. Together, these data demonstrate that sequential switching through IgG1 is redundant in sensitization, anaphylaxis, and the persistence of allergy, ultimately revealing that IgE derived from any switching source should be targeted by novel therapeutics seeking to ameliorate allergic diseases.