Abstract 476: Mast Cell--Mediated Neutrophil Influx Enhances Plaque Progression

Rationale: Activated mast cells have been identified in atherosclerotic plaques. As mast cells have the ability to release chemokines that mediate leukocyte fluxes, we propose that activated mast cells play a pivotal role in leukocyte recruitment during atherosclerosis. Methods and Results: Diet fed B-cell deficient apoE-/-muChain mice, which lack endogenous IgE, received 6 IgE or PBS injections over a period of 8 weeks. Mast cells in the aortic root were significantly more activated after IgE treatment and concomitantly, we detected an increase in plaque size (P=0.050). Intriguingly, a striking increase in the amount of perivascular neutrophils was observed in IgE treated mice (control: 57.6 ± 10.6 neutrophils/mm2 tissue; IgE: 183.0 ± 38.7 neutrophils/mm2 tissue; P=0.01). In order to investigate if activated mast cells can directly attract neutrophils, we injected C57Bl/6 or mast cell deficient Kit(W-sh/W-sh) mice intra-peritoneal with the mast cell activator 48/80. Interestingly, mast cell activation led to a massive neutrophil influx into the peritoneal cavity, while neutrophil numbers in mast cell deficient mice remained unaffected. To confirm these findings, we performed an in vitro migration assay. Indeed, supernatant of activated mast cells caused a 3-fold increase in neutrophil migration (P=0.007). Moreover, addition of anti-CXCR2 to the neutrophils resulted in a major reduction of migration (P=0.03) whereas anti-CXCR4 did not reduce migration significantly. Conclusions: Chemokines released from activated perivascular mast cells induce neutrophil recruitment to the atherosclerotic plaque, thereby aggravating the inflammatory response.