Description:
<jats:title>Abstract</jats:title><jats:p>Unmethylated CpG‐containing DNA plays a critical role in immunity via the augmentation of Th1 but suppression of Th2 T cell responses. We describe here that CpG motifs also redirect isotype production by murine B cells to "Th1‐like" Ig isotypes (IgG2a, IgG2b, and IgG3) while suppressing Th2 isotypes (IgG1 and IgE). Using genetically mutant B cells, we find that the IgG2a, IgG2b and IgG3 isotypes are transcriptionally regulated via the promotion of class‐switching, in a manner critically dependent upon TLR9 and MyD88. Thus, CpG DNA redirects Ig isotype production by regulating the specificity of class‐switch recombination.</jats:p>