MMP12 and rheumatoid arthritis: Since our results indicated that ST in UA show enriched expression of GM-CSF in the stromal cells and activin A in the SF, we next determined the expression of proteins associated with GM-CSF-driven polarization (activin A, MMP12, and TNFα) and M-CSF-driven polarization (CD209) (21) (Figure 2B) in ST CD163+ macrophages of persistent UA, UA>RA, UA>PsA, and in established RA and PsA (Figure 3A).