Fig. 1

Biochemical validation of differentially abundant proteins identified using isobaric tagging for relative and absolute quantitation (iTRAQ) proteomics. a and d Differential abundance of complement C1S subcomponent (C1S) and matrix metalloproteinase 2 as measured by iTRAQ MS and biochemical enzyme-linked immunosorbent assay (ELISA), respectively. Quantitative ELISA confirmed that (b) C1S is significantly decreased in the synovial fluid (SF) of non-responders (NR) compared with responders (R) to autologous chondrocyte implantation (ACI) prior to cartilage harvest (stage I [S1]; p = 0.04 by Student’s t test) (c) but was not significantly differentially abundant prior to chondrocyte implantation (stage II [S2]). Matrix metalloproteinase 3 (MMP3) (e) was not differentially abundant in response to cartilage harvest in ACI responders (f) but was biochemically confirmed to be differentially abundant in the SF of non-responders between stages I and II of the ACI procedure (p = 0.001 by Student’s t test)