Activated mast cells have been identified in the perivascular tissue of human coronary artery plaques. As mast cells have been described to release a whole array of chemokines including interleukin 8 (IL-8) and MIP1 α, we propose that activated mast cells play a pivotal role in leukocyte recruitment at advanced stages of atherosclerotic plaque development. Peritoneal mast cells of either C57Bl/6 or mast cell deficient Kit(W
−sh
/W
−sh
) mice were activated by injection of compound 48/80 (1.2 mg/kg). Interestingly, mast cell activation led to a massive neutrophil influx into the peritoneal cavity at 3 hours after activation (controls: 1 ± 0.7*10
4
Gr1
+
-neutrophils/ml up to 8 ± 0.2*10
4
Gr1
+
neutrophils/ml at 3 hours after activation, *P<0.05), while neutrophil numbers in Kit(W
−sh
/W
−sh
) mice were not affected by compound 48/80 administration. Moreover, increased levels of CXCR2
+
Gr1
+
neutrophils (t=0: 0.55 ± 0.07% versus t=3 hours: 1.00 ± 0.12%, *P<0.05) were observed after mast cell activation. Next, we investigated whether mast cell activation also translated in induced leukocyte adhesion to advanced atherosclerotic plaques. Adventitial mast cells of advanced collar aided carotid artery plaques were activated by local application of a dinitrophenyl-BSA (DNP) challenge in ApoE
−/−
mice. Three days later, the carotid artery segments carrying the plaques were isolated and perfused ex vivo with rhodamine labeled leukocytes, showing a dramatically increased number of adherent leukocytes after mast cell activation (49 ± 6 versus 19 ± 4 leukocytes/microscopic field for DNP versus control plaques, respectively, **P<0.001). Strikingly, antibody blockade of either the CXCR2 or VCAM-1 receptor VLA-4 on labeled leukocytes completely inhibited leukocyte adhesion to the atherosclerotic plaque (*P<0.05), while blockade of CCR1, -3 and -5 with Met-RANTES had no effect. In conclusion, our data suggest that chemokines such as IL-8 released from activated perivascular mast cells induce leukocyte recruitment and adhesion to the atherosclerotic plaque, aggravating the ongoing inflammatory response and thus effecting plaque destabilization. We propose that mast cell stabilization could be a new therapeutic approach in the prevention of acute coronary syndromes.
Ultrasound-Enhanced rt-PA Thrombolysis in an ex vivo Porcine Carotid Artery Model