The mean percentages of CD3+CD4+CD28null T cells out of CD3+CD4+ T cells were 5.1 ± 9.8%, 5.1 ± 6.8%, 4.6 ± 5.2% and 1.5 ± 4.5% for AS, PsA, RA and healthy controls (each with P < 0.001), respectively. This evidence concerns the gene CD4 and rheumatoid arthritis.