MMP9 and infection: To this end, the early release of 6 kDa early secretory antigenic target (ESAT-6) led to the activation of the epithelium, which facilitated the recruitment of macrophages to the site of infection through inducing the production of matrix metalloproteinase-9 (MMP-9) (Davis and Ramakrishnan, 2009; Volkman et al., 2010).