Increased CD74 expression in human atherosclerotic plaques: Contribution to inflammatory responses in vascular cells

AimsThe purpose of this study was to analyse the expression of CD74 in human atherosclerotic plaques and peripheral blood mononuclear cells (PBMC) as well as its potential participation in proinflammatory responses in cultured human vascular smooth muscle cells (VSMC).Methods and resultsCD74 expression was analysed in human atherosclerotic plaques (immunohistochemistry), PBMC (real-time PCR), and human aortic VSMC (real-time PCR and western blotting). Nuclear factor-κB (NF-κB) activation was assessed by southwestern histochemistry and electrophoretic mobility shift assay. Monocyte chemoattractant protein-1 (MCP-1) levels were studied by both real-time PCR and enzyme-linked immunosorbent assay. CD74 immunostaining was increased in the inflammatory vs. the fibrous region of atherosclerotic plaques (n = 70, 18.2 ± 1.3 vs. 7.8 ± 0.6 positive staining/mm², P < 0.001). CD74 colocalized with the transcription factor NF-κB in both VSMC and macrophages. In cultured VSMC, CD74 expression was induced by interferon γ (IFNγ). Incubation with an agonistic anti-CD74 antibody or with IFNγ elicited MCP-1 expression, which was prevented by AKT and γ-secretase inhibitors. Moreover, CD74 small-interfering RNA decreased NF-κB activation and MCP-1 production induced by IFNγ in VSMC. Finally, CD74 mRNA levels in PBMC from patients with carotid stenosis were higher than in healthy subjects (n = 20, 3 ± 0.5 vs. 2 ± 0.5 AU, P < 0.001). Additionally, a linear trend between CD74 mRNA expression tertiles and intima-media thickness (IMT) was observed in PBMC from asymptomatic subjects (n = 185, P < 0.001).ConclusionCD74 levels are increased in plaques and PBMC from patients with carotid stenosis and are associated with IMT in subjects free from clinical cardiovascular diseases. CD74 could be a novel therapeutic target to decrease the inflammatory response in atherosclerosis.