Myositis specific autoantibodies: changing insights in pathophysiology and clinical associations.

PURPOSE OF REVIEW Defined autoantibodies are found in about half of the patients with myositis. Traditionally, these autoantibodies have been divided into myositis specific autoantibodies (MSAs) and myositis associated autoantibodies. Several studies have shown that MSAs are associated with specific clinical characteristics and can aid our understanding of the pathophysiology of myositis. RECENT FINDINGS Recent studies suggest that some MSAs are markers of specific inflammatory muscle diseases (e.g., anti-SRP for an immune-mediated necrotizing myopathy) and not just of myositis in general. Furthermore, new insights are emerging about the pathophysiology of MSAs, in particular anti-Jo-1. Based on these new insights, an alternative hypothesis of the formation of anti-Jo-1 autoantibodies is presented in which the immune system itself rather than muscle is the site of antigen presentation. SUMMARY The recognition that some MSAs are markers of specific disease entities that were once commonly referred to as (poly)myositis, aids the development of better disease definitions. The changing insights in the function of the Jo-1 antigen and the emergence of new hypotheses on the formation of the Jo-1 antibody, open new avenues for future research aimed at unraveling the mystery of myositis.