CD28 and rheumatoid arthritis: At baseline, Tang in RA patients were characterized by a higher proportion of CD28nullcells (69.4 ± 8.6% vs 47.8 ± 9.5%, respectively, p = 0.003) and lower CD28-positive (32.7 ± 8.0% vs 52.2 ± 9.5%, respectively, p = 0.006) cells compared with HCs, showing an imbalance towards a CD28nullTang cell population.