MMP9 and aneurysm: CD4+ T cells and interferon-γ(a prototypical cytokine of Th1 cells, a subgroup of CD4+ T cells) has been demonstrated to stimulate MMP2 and MMP9 production from macrophages and SMCs, leading to structural extracellular matrix degradation and aortic dilation in murine calcium chloride (CaCl2)-induced aneurysm model (21).