To select genes for detailed analysis, we decided to focus on the genes that with high likelihood were differentially expressed with respect to arthritis and the presence of Mmp8. After selection of a group of seven genes, we found an increased expression of IL-1β, PTX3 and PROKR2 in arthritic joints from Mmp8-deficient mice compared with wildtype mice that were confirmed by real-time PCR assays. This evidence concerns the gene PROKR2 and arthritic joint disease.