Figure 3 Correlation of interferon γ (IFNγ)‐stimulated signal transducer and activator of transcription (STAT)1 phosphorylation with suppression of matrix metalloproteinase 13 (MMP13). (A) Chondrocytes were subjected to the indicated treatments with vehicle (control), interleukin (IL) 1 or IFNγ and extracts analysed for STAT1 tyrosine (tyr)‐701, serine (ser)‐727 phosphorylation and total STAT1. (B) Chondrocytes were pretreated with IFNγ for the indicated time points before additional stimulation with IL1β for 24 h. MMP13 mRNA and protein levels are shown. (C) Densitometric values of MMP13 reverse transcriptase‐PCR products in (B) and STAT1 phosphorylation in (A) quantified by NIH ImageJ 1.32j (National Institutes of Health, USA) software in arbitrary units were plotted against each other to depict the correlation between the two. (D) Western blots show that IL1β does not affect the IFNγ‐mediated activation (tyr/ser) of STAT1 in combined treatment.