HLA-DRB1 and rheumatoid arthritis: The role of protein citrullination in the context of Lyme arthritis remains relatively unexplored and deserves future examination, given that the HLA-DRB1 alleles 01:01 and 04:01, risk alleles in Lyme arthritis, contain the shared epitope, a five-residue sequence in the HLA-DRβ chain associated with severe rheumatoid arthritis (41).