IL-10 receptor signal transduction in B-CLL cells. MNCs (1 × 10⁷) containing a median of 93% CD19/CD5 positive B-CLL cells from 6 patients with B-CLL were stimulated with IL-10 (100 ng/mL) for 15 minutes. Whole cell extracts were prepared and subjected to EMSA using SIE as a probe as described in Materials and Methods. The lane to the far left identifies an EMSA with B-CLL cells (UPN 2) and the SIE probe in the absence of IL-10 (negative control). For each UPN, lane 1 identifies an EMSA with B-CLL cells and the SIE probe in the presence of IL-10, giving rise to SIF-A, -B, and -C complex as indicated on the right. For each UPN, lanes 2 and 3 identify an electrophoretic mobility supershift assay with B-CLL cells, the SIE probe, IL-10, and an antibody specific for STAT3 (lane 2) or STAT1 (lane 3). The arrows identify STAT1 and STAT3 MoAb-mediated supershift in all six patient samples.