MMP12 and colitis: The gene encoding matrix metalloproteinase Mmp2, which is expressed by fibroblasts and endothelial cells in the lung but not immune cells, was similarly increased in whole lung tissue by DSS treatment of C57BL/6 and TCRδ-/- mice, while Mmp12 gene expression which is predominately expressed by macrophages, was mildly increased in C57BL/6 mice harboring colitis but markedly increased in whole lung tissue of TCRδ-/- mice with colitis (Figure 5B).