Differentially expressed protein spots identified by 2-DE image analysis. The original 2-DE images representing all protein spots present in serum samples from the nonresponder group (A), the responder group (B), and the healthy control group (C). The enlarged images (D) showing the magnified regions 1–3 of the corresponding 2-DE gels. Nine identified protein spots (a-i, arrows showing the corresponding locations) with significantly differential expressions among the three groups were visualised. Protein spots a to i showed obviously decreased expressions in the nonresponders compared with the responders and healthy controls.