The inflammatory response in extravasated leukocytes in patients with coronary artery disease

Abstract

Coronary artery disease (CAD) is a manifestation of a chronic inflammation in the coronary arteries. The inflammatory process results in accumulation of monocyte derived cells and formation of atherosclerotic plaques in the intima of the vessel wall. Neutrophils are mainly associated with ruptured plaques and the precise role in CAD is not fully known. Extravasation into local inflammatory sites is coordinated by adhesion molecules and chemokines and transforms the leukocytes into activated tissue dwelling cells. The aim of this thesis was to investigate extravasated monocytes and neutrophils in patients with stable CAD. A skin chamber method was applied in order to induce a local inflammation from which extravasated cells were collected.

Paper I and II describes extravasated monocytes. Patients with CAD had a similar number of extravasated monocytes in the chamber exudate compared to healthy subjects. The expression of CD11b following extravasation was lower in patients with CAD compared to healthy controls. This might result in an increased retention of monocytes at a local inflammatory site. Other markers associated with monocyte extravasation, VLA-4 and CX3CR1, were not altered. Extravasated monocytes were further analyzed for functional alterations. Markers associated with antigen presentation, HLA-DR and CD86, and binding of modified cholesterol, CD36 and scavenger receptor A1 (SR-A1) had an increased expression following extravasation compared to in circulation. Furthermore, the binding of acetylated low density lipoprotein (acLDL) increased following extravasation. Monocytes from patients and controls had a similar functional response. However, the chamber fluid from patients with CAD enhanced the expression of CD36 following in vitro stimulation of mononuclear cells.

Paper III and IV describes extravasated neutrophils. Extravasated neutrophils from patients with CAD had a significantly lower expression of CD11b and a lower production of reactive oxygen species (ROS) following stimulation compared to healthy controls. This might indicate a refractory stage following extravasation in patients with CAD. The gene expression in extravasated neutrophils was assessed by a gene array. A general induction in the IL-1 axis was seen following extravasation and was associated with an increased expression of chemokines. Expression of IL-1R on human neutrophils was confirmed with flow cytometry and electron microscopy and stimulation with IL-1 resulted in CCL and CXCL chemokine gene and protein expressions. Compared to healthy controls, extravasated neutrophils from patients with CAD had significantly increased expressions of CCL20 and CXCL2. This finding indicates that neutrophils may have an immuno-modulatory role at local inflammatory sites and that patients with CAD have a chemokine profile that could enhance the pathological processes in atherosclerosis.

The major findings indicate a potential mechanism for monocyte entrapment at local inflammatory sites. In addition, the local inflammatory milieu in patients with CAD might be pro-atherosclerotic. Neutrophils from patients with CAD had an altered responsiveness and could be refractory. Furthermore, neutrophils may alter the localinflammatory milieu by the production of chemokines.