Control of germinal center B cell survival and IgE production by an adaptor molecule containing PH and SH2 domains,...

The germinal centers (GCs) are structure found within secondary lymphoid organs and are important for the antibody-producing response against foreign antigens. In GCs, antigen-specific B cells proliferate intensely, inducing immunoglobulin class switching. Recent studies have shown that GCs are also an important site for class switching to IgE, which is implicated in allergy. However, the mechanisms by which IgE production is regulated in GCs remain unclear. Here, we found impairment in IgE-specific production and a reduction of GC B cells after immunization in mice deficient in the Aps/Sh2b2 gene encoding the Lnk/Sh2b family adaptor protein Aps. GC B cells express higher levels of the Aps gene than non-GC B cells, and cell death of Aps^-/- GC B cells is enhanced compared to wild-type GC B cells. An in vitro culture system with purified Aps^-/- B cells induced the same level of IgE production and frequencies of IgE⁺ B cells as wild-type B cells. We found that Aps deficiency in B cells resulted in augmented depletion of IgE⁺ blasts by B cell receptor crosslinking with anti-CD79b antibodies compared to wild-type IgE⁺ cells. These results suggest that Aps regulates IgE production by controlling the survival of GC B cells and IgE⁺ plasma cells and may serve as a potential therapeutic target to control IgE production.