Serum Antibodies against Porphyromonas gingivalis GroEL are Insufficient to Induce P.gingivalis-accelerated Atherosclerosis

Abstract

Periodontitis is associated with an increased risk of atherosclerosis, and accumulating evidence suggests a positive association between anti-heat shock protein 60 autoantibodies and atherosclerosis in humans. Heat shock proteins of the GroEL or HSP60 class are highly conserved proteins essential to all living organisms. In this study, we examined the effects of immunization with recombinant HSP60 from Porphyromonas gingivalis on antibody responses and the development of atherosclerosis. Atherosclerosis was examined in BALB/c mice fed a high-fat diet or a regular chow diet following subcutaneous immunization with GroEL or intravenous injection with P. gingivalis. The proximal aorta lesion area, serum levels of anti-GroEL antibodies, CRP and MCP-1 levels, expression of HSPs, and inflammatory mediator expression in aorta were measured. Early atherosclerotic lesion area was substantially lower in HFD-fed mice immunized with GroEL compared to P.gingivalis-challenged mice, although significant atherosclerotic lesions, serum immunoglobulin G responses to GroEL, and HSP60 were detected in GroEL-immunized mice. Immunohistochemical staining confirmed strong HSP60 expression in the vascular wall of HFD-fed mice compared to RD-fed mice. Although immunization of the HFD-fed mice with GroEL slightly enhanced serum MCP-1 secretion as well as CD40/40L and LOX-1 expression in the aorta, it did not affect serum CRP levels. These results suggest that immune response cross-reactivity to bacterial HSPs, including periodontal pathogens, with arterial endothelial cells expressing HSP60 are not associated with atherosclerosis severity caused by P.gingivalis challenge. This may explain why antibody responses to bacterial HSPs are an unlikely major risk factor for coronary artery disease.