Western blot analysis of responder and nonresponder sera. To validate results of serum proteome profiling, western blot analyses for haptoglobin (Hp)-α1, Hp-α2, apolipoprotein (Apo)C-III and ApoA-II were carried out. Serum samples from responders (n = 5) and nonresponders (n = 5) were subjected to western blot analysis with antibodies against the mentioned proteins. At baseline (V1), responder sera revealed a significant upregulation of Hp-α1 and Hp-α2 band intensities in comparison with nonresponders. These results were also detected after 6 months of etanercept treatment (V6). In contrast, the ApoC-III upregulation in responders could only be confirmed at baseline (V1). ApoA-II levels were found to be significantly upregulated in responders only after 3 months (V5) and 6 months (V6) of therapy in comparison with nonresponders.