Purpose of review: The purpose of this review is to describe how the current knowledge of antibodies to citrullinated protein antigens in rheumatoid arthritis and related conditions emerged; to discuss the diagnostic and prognostic value associated with antibodies to citrullinated protein antigens as a biomarker; and most importantly for this review, to discuss the potential pathogenetic significance of these antibodies.
Recent findings: Antibodies to citrullinated protein antigens have evolved from being mainly a diagnostic marker, to being recognized as something that can help us understand fundamental etiologic and pathogenetic features of rheumatoid arthritis. Fundamental in this context is the finding that rheumatoid arthritis can be divided into two distinct subsets by means of presence or absence of antibodies to citrullinated protein antigens. Thus, several genetic as well as environmental risk factors differ between these two variants of rheumatoid arthritis. From analysis of these genetic and environmental risk factors, new testable hypotheses have been produced concerning triggering of antibodies to citrullinated protein antigens, and potential pathogenicity of antibodies to citrullinated protein antigens and accompanying immune reactions.
Summary: The implications of the findings are that antibodies to citrullinated protein antigens can be used for early and precise diagnosis of a subset of rheumatoid arthritis with worse prognosis than other polyarthritides, and that a new basis is formed for etiologic and pathogenetic studies of antibodies to citrullinated protein antigens-positive rheumatoid arthritis.