Figure 2 Optimal blood incubation conditions for interleukin (IL)1-ra production facilitate the synthesis of matrix metalloproteinase (MMP)-9, which is reversed by sodium citrate (SC) addition. (A) Comparison of the MMP-9, MMP-2, MMP-3, and MMP-7 protein concentrations in human blood samples before (baseline level) and after incubation at 37°C for 24 h. Two-way analysis of variance (ANOVA) revealed a statistically significant increase in the levels of MMP-9 at 24 h after incubation (*** P<0.001; nonsignificant [ns], P>0.01). (B) Two-way ANOVA revealed that the presence of SC has a negative impact on MMP-9 secretion by blood cells compared with saline controls (* P<0.01). The figure was created using ImageJ software version 1.53e; Java 1.8.0_172.