STAT3 and atrial fibrillation: As expected, inhibition of STAT3 activation by Stattic abrogated the expansion of AF-driven CD14+HLA-DR–/low MDSC similar to that done by neutralizing antibodies against IL-6 and IL-10 (Figure 5B), validating the critical role of both IL-6/IL-10 and their triggered downstream STAT3 signal in contributing to AF-driven expansion of CD14+HLA-DR–/low MDSC.