MMP8 and arthritic joint disease: Changes in the expression of these three genes exemplify different ways in which the lack of MMP-8 led to an aggravation of arthritis: promotion of inflammation by IL-1β and other molecules like PTX3, induction of maturation and activation of osteoclasts by IL-1β and PROKR2, and enhanced inflammatory infiltrate by IL-1β and possibly PROKR2 - however, other contributing mechanisms are possible as only a fraction of the genes with possible differential expression were analyzed.