CALR and rheumatoid arthritis: This citrullinated calreticulin preferentially binds to the shared epitope (SE), a sequence motif in the β1 domain of the HLA-DR molecule that is found in 90% of rheumatoid arthritis patients, and potentiates 10,000-fold greater SE-activated signaling in innate immune cells compared to non-citrullinated calreticulin (45, 46).