CD28 and rheumatoid arthritis: After stimulation of T cells for 48 hours with anti-CD3-mAb and anti-CD28-mAb together with IL-2, 2.3% ± 0.3% T cells went into apoptosis (Annexin-V-positive, PI-negative) in HDs compared with 2.6% ± 0.5% in patients with RA (p = 0.674).