STAT3 and B-cell chronic lymphocytic leukemia: Because IL-6 has been found to increase the levels of serine pSTAT3 and induce the phosphorylation of STAT3 on tyrosine residues [15], we incubated CLL cells with 30 mg/ml rhIL-6 for 20 minutes and analyzed their miR-155 expression levels at different times following incubation using RT-PCR and relative qRT-PCR.