IgE isotype switch and IgE production are enhanced in IL-21-deficient but not IFN-γ-deficient mice in a Th2-biased response

IgE plays a critical role in the pathogenesis of allergy and asthma. Therefore, suppression of IgE production would provide therapeutic benefits to patients suffering from these diseases. We have reported that the production of IgE is regulated differently in the spleen vs. the draining lymph nodes (LN). IgE isotype switch and IgE producing B cell expansion occur in the draining LN after antigen (Ag) immunization, but do not happen in the spleen. In addition, a population of pre-existing IgE+ cells is observed in the spleen of normal or sham immunized mice, but is not present in the draining LN. To further understand the regulation of IgE production in different lymphoid organs, and the potential inhibitory factors of IgE isotype switch in the spleen, the involvement of IL-21 and IFN-γ in regulating IgE production was investigated by using the IL-21 and the IFN-γ deficient mice. We found that in the absence of IL-21 IgE isotype switch and IgE+ cell clonal expansion were dramatically enhanced in the spleen and IgE isotype switch was partially increased in the draining LN. In addition, IgE production of the pre-existing CD19−CD5+B220low IgE+ cells in the spleen was also increased in the absence of IL-21 under physiological conditions. In contrast, using the IFN-γ deficient mice, we did not observe a negative impact of IFN-γ on either IgE isotype switch or IgE production. Our data suggest that IL-21 appears to be a critical cytokine to keep low IgE levels under physiological and pathological conditions.