Abstract 120: Does Complement Contribute to Intimal Thickening of Injured Carotid Arteries? Insights from Immune Deficient Mice and Complement Depletion Strategy
Background: Immune-deficient Rag-1KO mice develop exuberant intimal thickening in response to arterial injury when compared to immune-competent mice. Reconstitution of Rag-1KO mice with immunoglobulin significantly reduced the exuberant intimal thickening, strongly supporting a direct role for the humoral immune system in modulating intimal thickening. In the current report, we hypothesized that the complement pathway of the innate immune response contributes to intimal thickening after arterial injury. We used Rag-1KO mice which lack T cells, B cells, and immunoglobulin, but have an intact complement system.
Methods and Results: We first determined the relative presence of complement component C3 in injured arteries of wild-type (WT) and Rag-1KO mice by immuno-staining. Injured arteries from WT mice had scant C3 positive staining, but Rag-1KO mice had focal staining of C3 in the intima. Immuno-precipitation of C3 from serum showed that Rag-1KO mice had increased presence of a ∼115kDa-sized fragment but reduced presence of a ∼40kDa-sized fragment compared with WT serum 21 days after injury (n=2 per group). We then tested the role of complement in vivo by treating Rag-1KO mice with complement-depleting cobra venom factor (CVF) at a dose of 25mcg/mouse starting 4 days prior to injury, and then every 4 days until euthanasia 21 days after injury. Depletion of complement in Rag-1KO mice resulted in significantly reduced intimal thickening area and intima:media ratio (P<0.05; Table 1⇓). CVF treatment had no significant effect on medial area.
Conclusion: Our results indicate that the complement component of the innate immune system contributes to intimal thickening after arterial injury. Since Rag-1KO mice lack immunoglobulin to activate the classic complement pathway, our results strongly support the notion that the alternative pathway is involved in this process.