Detection of citrullinated proteins in IC of RA SF (a) and RA serum (b) after immunoprecipitation. 1D-PAGE and AMC staining were performed on the isolated IC and the flow through after IP, from synovial fluid and serum of RA patients. Where (+) is the positive control for AMC staining; the flow-through is shown in lane 1 and the IC-fraction in lane 2. Citrullinated proteins could be detected in the IC isolated by IP in the SF of RA patients (a) and were absent in the sera of RA patients (b). In the fraction indicated by "x";, immunoglobulins, serum albumin and Fibβ were identified by mass spectrometry.