Chlamydophila pneumoniae Infection of Human Aortic Endothelial Cells Induces the Expression of FC γ Receptor II (FcγRII)

Chronic endothelial infection is believed to be one of the factors able to cause endothelial cell damage and trigger the onset of human atherosclerosis. Chlamydophila pneumoniae infects endothelial cells and has received special attention because of both epidemiological and experimental evidence supporting its role as a risk factor for atherosclerosis. It is also possible that otherwise independent risk factors for atherosclerosis may have synergistic effects. Immune phenomena, such as the formation of circulating immune complexes (IC) containing modified LDL and corresponding antibodies, have been linked to the development of coronary artery disease. The antibodies involved in the immune response to modified lipoproteins are predominantly of the pro-inflammatory IgG1 and IgG3 subclasses. However, it is difficult to understand how circulating IC could cause endothelial damage and initiate the atherosclerotic process, unless they were formed in the subendothelial space or immobilized by endothelial cells. The last hypothesis would be possible if endothelial cells expressed Fcγ receptors. Healthy endothelial cells do not express Fcγ receptors, but endothelial cells infected by a variety of infectious agents do. Thus we decided to investigate whether infection of endothelial cells with C. pneumoniae is also able to cause the expression of Fcγ receptors. The expression of Fcγ receptors (CD64, 32, and 16) on human aortic endothelial cells infected with C. pneumoniae for 4, 24, 36, and 48 h was studied by flow cytometry. Twenty-four hours after infection 30–40% of the endothelial cells had detectable inclusion bodies, 8–9% of the total number of cells (approximately 25% of the infected cells) expressed FcγRII, and about 1.5–2% (5% of infected cells) expressed FcγRI and FcγRIII. Double-staining studies confirmed that the expression of FcγRII was limited to C. pneumoniae-infected endothelial cells. We conclude that C. pneumoniae infection induces primarily the expression of FcγRII by endothelial cells and this may be a significant link between two proposed pathogenic mechanisms involved in the pathogenesis of human atherosclerosis.