Abstract 122: Circulating CD28- T Cells Are Associated with Histological Features of Carotid Plaque Instability

Abstract

Background: Circulating CD28- T-cells have been found to be higher in patients with acute coronary syndromes, suggesting a role for these cells in plaque instability. However, the association between circulating CD28- T-cells and carotid plaque instability as assessed by histology/immunohistochemistry has not been investigated. Methods/Results: 40 patients referred for carotid endarterectomy were recruited pre-operatively at the Royal Victoria Hospital in Montreal, Canada. A blood sample was obtained pre-operatively. Flow cytometry was performed on whole blood using a CD3, CD4, CD28 antibody cocktail (eBioscience, San Diego, United States) and a BD Bioscience (Mississauga, Canada) flow cytometer. Data was acquired as percentage of CD4+CD28- T-cells. The carotid plaque specimen was obtained from the operating room, fixed, decalcified, embedded in paraffin, and sections of 4μm were obtained from the site of maximum stenosis. Sections were stained with hematoxylin and eosin and with anti-CD3 (lymphocytes), anti-CD68 (macrophages/foam cells), and von Willebrand Factor (vWF, neovessels, all antibodies from Dako, Burlington, Canada). A vascular pathologist classified the plaques according to American Heart Association (AHA) classifications and graded CD3, CD68, and vWF staining on a semi-quantitative scale. Patients with more advanced lesions (AHA type 5 or 6) had a greater percentage of circulating CD4+CD28- T-cells [2.9% (2.7-5.7)] compared to patients with lower classifications [1.6% (1.0-4.2), P<0.05]. Furthermore, patients with plaques that had ≥10 new vessels per section (feature of plaque instability) had a median of 4.5% [2.8-8.0] CD4+CD28- T-cells whereas patients with <10 new vessels per section had only 2.3% [0.8-5.0] (P<0.05). There were no significant differences when patients were separated according to high/low plaque lymphocytes/macrophages. Conclusion: We have shown that circulating CD28- T-cells are found in greater amounts in patients who have more advanced/unstable carotid plaques as assessed by histology and immunohistochemistry. This may point to a role for CD28- T-cells in the pathogenesis of atherosclerosis. Further studies are currently being carried out to confirm these results.