STAT3 and viral infectious disease: Remarkably, when nuclear translocation of STAT1 was investigated, we found that although viral infection increased the expression level of pSTAT1701, most of the pSTAT1701 localized in the cytoplasm instead of the nucleus, but when STAT3 was knocked down by siRNA, a significant amount of pSTAT1701 was translocated into the nucleus upon infection (Figure 5A,B).