Ligation of CD40 Activates Interleukin 1β-converting Enzyme (Caspase-1) Activity in Vascular Smooth Muscle and Endothelial Cells and Promotes Elaboration of Active Interleukin 1β

Abstract Inflammation contributes to a variety of arterial diseases including atherosclerosis. Interleukin 1β (IL-1β) in its activated mature 17-kDa form may mediate aspects of vascular inflammation. As shown previously, human vascular wall cells, such as smooth muscle cells (SMC), express the IL-1β precursor upon stimulation and the IL-1β-converting enzyme (ICE) constitutively but do not produce mature IL-1β or express ICE activity. How SMC, the most numerous cell type in arteries, may release active IL-1β has therefore remained a perplexing problem. We report here that stimulation of human vascular SMC and endothelial cells (EC) through CD40 ligand, a mediator recently localized in human atheroma, induced elaboration of the IL-1β precursor as well as activation of cell-associated ICE. In addition to the constitutively expressed 45- and 30-kDa immunoreactive ICE proteins, vascular cells incubated with recombinant human CD40 ligand (rCD40L) (but not IL-1 or TNF) showed an increase of a 20-kDa immunoreactive ICE protein by Western blot analysis. Furthermore, SMC and EC stimulated through rCD40L processed recombinant human IL-1β precursor (pIL-1β), generating a cleavage product of approximately 17 kDa. Appearance of both the 20-kDa immunoreactive ICE protein and pIL-1β processing activity required at least 6 h of stimulation with 0.3 or 1.0 μg/ml rCD40L, respectively, and was inhibited by pre-incubation of the ligand with an anti-CD40L antibody. Stimulation of vascular SMC and EC through rCD40L resulted in the release of biologically active IL-1β, indicating processing of the native IL-1β precursor induced by the ligand. These findings establish a novel mechanism of IL-1β activation in human vascular cells and, moreover, indicate a new pathway of ICE-activation, which could participate in inflammatory aspects of atherogenesis and other disease states.