CD28 and rheumatoid arthritis: rs3181096 in the CD28 gene was associated with RA in the homozygous model (CC vs. TT, p = 0.047, OR = 0.309, 95% CI = 0.92–1.04) and recessive model (CC + CT vs. TT, p = 0.035, OR = 0.297, 95% CI = 0.09–0.98).