IL-10 inhibits the SEB reduction of p27^Kip1and prevents SEB-induced upregulation of cyclins D2 and D3 in CD4⁺ T cells. (A) PBMCs were incubated in 6-well plates at 6 × 10⁵ cells/mL along with IL-10 at 10 U/mL or media only. After 2 days of incubation, media alone or SEB at 100 pg/mL was added. The cells were further incubated until the indicated harvest day. Cells were harvested and CD4⁺ T cells were separated and collected by negative selection affinity chromatography. Lysates from these cells were subjected to SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western analysis using antibodies specific for p27^Kip1, cyclin D2, and cyclin D3. The lower band in the cyclin D2 doublet represents the faster-migrating activated form of cyclin D2. (B) Quantitation was performed by densitometric analysis of bands from day 3.5. The differences between SEB treatment and treatment with IL-10 and SEB were found to be statistically significant for all immunoblots (P < .001) by the Student’s t-test.