Biological markers in inflammatory rheumatic diseases.

Biological markers of inflammation are useful for the diagnosis and the monitoring of inflammatory rheumatisms and connective tissue diseases. These markers are not specific, and often poorly correlate with the long term evolution of the disease. C-reactive protein (CRP) is a sensitive marker, and is used to monitor inflammatory and infectious diseases. In rheumatoid arthritis (RA), CRP correlates with disease activity and response to therapy, and CRP levels are influenced by disease-modifying drugs and corticosteroids. Serum amyloid A (SAA) is another acute phase protein (APP) which appears in RA as a more sensitive marker than CRP. Several antinuclear antibodies serve as markers of systemic disorders; they are not implicated in the disease by themselves, but their production could be related to the genetic background underlying the pathogenesis of the disease. In systemic lupus erythematosus (SLE), the titer of anti-ds DNA antibodies often correlates with disease activity. DNA is poorly immunogenic and the production of anti-ds DNA antibodies could be linked to the association of DNA with more immunogenic protein antigens. Cellular DNA is associated with proteins in nucleosomes and it now appears more appropriate to consider the anti-DNA antibody production as a response to a DNA-protein complex. Antibodies can be directed to histones and DNA-protein complexes such as transcription or replication complexes. Antibodies to ribonuclear proteins are associated with different disease subsets and help to define the prognosis in SLE and connective tissue diseases. The identification of antibodies directed against proteins and RNA components is still a field of research.