Immunohistochemical staining of human atherosclerotic plaques revealed expression of the tumor necrosis factor receptor superfamily (TNFRSF) 12 in regions rich in macrophage/foam cells. The role of TNFRSF12 in the functioning of monocytes in relation to atherogenesis was investigated by analysis of cellular events after stimulation of TNFRSF12 in a human macrophage-like cell line, THP-1. Activation of the THP-1 cells on plates coated with monoclonal antibody against TNFRSF12 induced the expression of matrix metalloproteinases (MMPs) -1, -9, and -13. Furthermore, the expression patterns of TNFRSF12 and the MMPs overlapped in atherosclerotic plaques. Signaling of TNFRSF12 may thus contribute to the induction of extracellular matrix degrading enzymes in macrophages.