However, the expression of acid phosphatase 5, tartrate-resistant (ACP5), and matrix metalloproteinase (MMP)-9 was comparable in cells treated with M-CSF and sRANKL in the presence or absence of IL-9 in cells derived from PB of HC, PB, and SF of RA patients (Figure 1D and E). Here, MMP9 is linked to rheumatoid arthritis.