Modulation of the humoral immune response by constitutively active STAT6 expression in murine B cells.

The transcription factor STAT6 regulates gene expression in response to IL-4 and IL-13. To further investigate how activated STAT6 modulates B cells development and function in vivo, we characterized mice that express a constitutively active version specifically in B cells. CD19Cre_STAT6vt mice show spontaneous phosphorylation and nuclear translocation of STAT6 in B cells. About 80 genes were more than twofold up- or downregulated in splenic B cells from CD19Cre_STAT6vt as compared to control mice. B cell development, tissue localization, and populations of follicular and marginal zone B cells, B1 B cells, GC B cells, and plasma cells (PCs) appeared to be normal. However, the number of IgE+ and IgG1+ GC B cells and PCs as well as serum IgE and IgG1 levels were increased in CD19Cre_STAT6vt mice. Infection with Lymphocytic choriomeningitis virus associated with high levels of TNF and IFN-γ did not prevent the development of a significantly increased IgE and IgG1 response against the virus in CD19Cre_STAT6vt mice. These results suggest that prolonged STAT6 activation during chronic allergic inflammation may result in IgE responses during subsequent viral or bacterial infection that could further stimulate mast cell activation even in the absence of the initial allergic response.

Identification of Novel STAT6-Regulated Proteins in Mouse B Cells by Comparative Transcriptome and Proteome Analysis.

The transcription factor STAT6 plays a key role in mediating signaling downstream of the receptors for IL-4 and IL-13. In B cells, STAT6 is required for class switch recombination to IgE and for germinal center formation during type 2 immune responses directed against allergens or helminths. In this study, we compared the transcriptomes and proteomes of primary mouse B cells from wild-type and STAT6-deficient mice cultured for 4 d in the presence or absence of IL-4. Microarray analysis revealed that 214 mRNAs were upregulated and 149 were downregulated >3-fold by IL-4 in a STAT6-dependent manner. Across all samples, ∼5000 proteins were identified by label-free quantitative liquid chromatography/mass spectrometry. A total of 149 proteins was found to be differentially expressed >3-fold between IL-4-stimulated wild-type and STAT6-/- B cells (75 upregulated and 74 downregulated). Comparative analysis of the proteome and transcriptome revealed that expression of these proteins was mainly regulated at the transcriptional level, which argues against a major role for posttranscriptional mechanisms that modulate the STAT6-dependent proteome. Nine proteins were selected for confirmation by flow cytometry or Western blot. We show that CD30, CD79b, SLP-76, DEC205, IL-5Rα, STAT5, and Thy1 are induced by IL-4 in a STAT6-dependent manner. In contrast, Syk and Fc receptor-like 1 were downregulated. This dataset provides a framework for further functional analysis of newly identified IL-4-regulated proteins in B cells that may contribute to germinal center formation and IgE switching in type 2 immunity.