HLA-DRB1 and rheumatoid arthritis: We did not find an association between HLA-DRB1 SE and RF in anti-CCP2-negative RA, supporting data generated from single-cell RNA sequencing of RF-positive and ACPA-positive B cells, which suggest a T cell-dependent affinity maturation for the generation of ACPA, but innate immune pathways for the generation of RF [37].