Serum proteome profiles of responders and nonresponders to etanercept treatment in rheumatoid arthritis patients. Serum samples of responders (n = 5) and nonresponders (n = 5) were pooled after immunodepletion and subjected to two-dimensional differential gel electrophoresis analysis. Protein spot identification in serum proteome profiles of responders (R) and nonresponders (NR) was performed by subsequent mass spectrometry. (A) Prior to initiation of etanercept treatment (V1), five proteins were found to be significantly upregulated in responders including vitamin D-binding protein (VDBP), haptoglobin (Hp)-α1, Hp-α2, vitronectin and apolipoprotein C-III. (B) After 6 months of therapy (V6), VDBP, Hp-α2, Hp-β and α1-antitrypsin were found at significantly elevated levels in responder sera. MW, molecular weight.