MMP9 and infection: The separation of pre- and post-infection groups was positively influenced by peripheral monocyte trafficking, skin mucus IgM levels and protease activity, and the gene expression levels of transforming growth factor-beta (tgfb), spermine synthase (sms), nuclear factor kappa B (nfkb), interleukins 6 and 8 (il6 and il8, respectively), cluster of differentiation 209 antigen-like protein C (cd209c), matrix metallopeptidase 9 (mmp9) and tumor necrosis factor-alpha (tnfa) in the head kidney (Figure 2).