Among the HLA-DRB1 alleles they tested (five SE alleles, *01:01, *04:01, *04:04, *04:05, and *10:01, and a non-SE allele, *09:01, frequently observed in Asian populations), *10:01 showed the strongest interaction with CS, and the genotype heterozygous for *04:05 and *09:01 conferred the highest risk of both ACPA-positive and -negative RA development in the interaction with CS. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.