Fig. 5

Identification of the citrullinated proteins in U937 cells after being differentiated to macrophages. a ACPAs bound to cell protein extract of U937 cells, differentiated macrophages, and macrophages stimulated with LPS for 24 h in 50 kDa and 48 kDa bands. b APCAs (−) RA sera did not bind to protein extract of U937 cells, differentiated macrophages, and macrophages stimulated with LPS. c Following excision, these bands were sent for proteomic analysis. After series Western blot analysis, we confirmed that antibody against plasminogen activator inhibitor-2 (PAI-2) reacted with cell protein extract of U937 cells, U937 differentiated macrophages, and macrophages stimulated with LPS in the 48 kDa band and the same pattern with those recognized by ACPAs. d We used self-purified ACPAs as a probe to immunoprecipitated citrullinated protein from cell lysate of the differentiated macrophages and macrophages stimulated with LPS. We showed the presence of PAI-2 in these citrullinated proteins after Western blot analysis using anti-PAI-2 as a probe