MMP9 and Zika virus infectious disease: Consistent with this, western blotting and gelatin zymography assays revealed that ZIKV infection, detected by NS1 expression, increased protein levels and gelatinase activity of MMP9 in the testes (Fig 1H), whereas MMP2 activity was not changed in infected testes, suggesting that MMP2 was constitutively expressed in vivo and was not altered by ZIKV infection.