Novel approach for discovery of biomarkers by comprehensive analysis of immune complexes

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We proposed a novel proteomic strategy (immune complexome analysis) consisting of ICs separation from serum and direct tryptic digestion followed by nano-liquid chromatography-tandem mass spectrometry for the identification and profiling of antigens in circulating immune complexes (CICs). We applied this strategy to the analysis of CICs in rheumatoid arthritis (RA). Sera samples from healthy donors and osteoarthritis patients were used as controls. CIC-associated thrombospondin-1 (TSP-1) was found in 81%, and CIC-associated platelet factor 4 (PF4) was found in 52% of established RA patients, but neither protein was found in CICs from any of the controls. Furthermore, CIC-associated TSP-1 was found only in early RA patients and was found in neither disease controls nor healthy donors. It was also found that seronegative early RA patients, who lack lacking RF and anti-CCP antibody markers, had CIC-associated TSP-1.