MMP9 and influenza: Indeed, while LYVE-1-expressing macrophages control arterial stiffness through modulation of the metalloproteinase-dependent proteolysis of the MMP-9 matrix (Lim et al., 2018), the expression of the MMPs inhibitor TIMP1 is related to the frequency of pulmonary macrophages and is involved in influenza-induced lung injury (Allen et al., 2018) and CXCL7 is a known attractant of macrophages in lung inflammation (Unver et al., 2015).