Expression of BMP receptors and Smad1 in human CD4⁺ T lymphocytes. Human CD4⁺ T lymphocytes were either untreated or stimulated with anti-CD3 plus anti-CD28 mAbs for the indicated time intervals and RT-PCRs were performed using primers specific for the indicated genes. Primer pair for BMPR-Ib has been confirmed to generate the anticipated product in other cell types (data not shown).