CD28 and rheumatoid arthritis: The CD28 rs1980422 CC genotype is associated with both rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) in rheumatoid arthritis (RA) (35, 36), while polymorphisms in ICOS rs6726035, PD1 rs36084323, DNAM1 rs763361, and TIM3 rs10515746 also act as related factors in RA development (37–40).