Indeed, recent studies in ehrlichial murine models have shown that IL-21 and IFNγ from Th1-Tfh cells were specifically required to induce Tbet+ B cells and class switching to cytophilic IgG2c [130] and Tbet expression in B cells is required for IgG2a/c switching in viral infection [131]. This evidence concerns the gene TBX21 and viral infectious disease.