Atherosclerosis, inflammation, and infection

In recent years, it has been shown that inflammation plays an important role in the pathogenesis of atherosclerosis. Activated macrophages, T lymphocytes, and mast cells are present in atherosclerotic plaques, which has led to the notion that the inflammatory response is an immune-mediated process. Complicated lesions, moreover, appear to be associated with an increase in the amount of the inflammatory response and in these patients, increased levels of acute phase proteins are present. The appreciation that atherosclerosis is an immune-mediated inflammatory disease has also led to renewed interest in the potential role of infectious agents in initiating or modulating atherosclerosis. Seroepidemiological studies have shown raised antibody titres against several micro-organisms. However, as yet, there are hardly any data available that provide a sound scientific basis for an infectious origin. Of all potential candidate organisms, Chlamydia pneumoniae appears as the one most likely involved in atherogenesis. C. pneumoniae has been retrieved from atherosclerotic tissues; the level of raised plasma titres correlates with the severity of symptomatic atherosclerotic disease; and the incidence of C. pneumoniae-responsive T cells in peripheral blood is increased in patients with coronary heart disease. It also appears that in some patients T cells generated from atherosclerotic plaques respond to C. pneumoniae. At the present state of knowledge, however, it is fair to state that the relationship between infection, intraplaque inflammation, and atherosclerosis still remains hypothetical, despite the increasing evidence that such a relationship could exist.