Mannose-binding lectin (MBL) and the lectin complement pathway play a role in cutaneous ischemia and reperfusion injury

Objectives: Cutaneous ischemia/reperfusion (CI/R) injury has shown to play a significant role in chronic wounds such as decubitus ulcers, diabetic foot ulcers, atherosclerotic lesions, and venous stasis wounds. CI/R also plays a role in free tissue transfer in reconstructive microsurgery and has been linked to clinical burn-depth progression after thermal injury. While the role of the complement system has been elucidated in multiple organ systems, evidence is lacking with respect to its role in the skin. Therefore, we evaluated the role of the complement system in CI/R injury. Methods: Using a single pedicle skin flap mouse model of acute CI/R, we performed CI/R in wild-type (WT) mice and complement knock out (KO) mice, deficient in either C1q (C1q KO; classical pathway inhibition), mannose-binding lectin (MBL null; lectin pathway inhibition) or factor B (H2Bf KO; alternative pathway inhibition). Following 10 h ischemia and 7 days reperfusion, mice were sacrificed, flaps harvested and flap viability assessed via Image J software. The flap necrotic area was expressed as % total flap area. In another group, mice were sacrificed following CI/R with 10 h ischemia and 48 h reperfusion. Two cranial skin flap samples were taken for gene expression analysis of IL1b, IL6, TNF alpha, ICAM1, VCAM1, IL10, IL13 using realtime polymerase chain reaction (RT-PCR). Results: Following CI/R, MBL null mice had a statistically significant smaller %necrotic flap area compared to WT mice (10.6 vs. 43.1%; p<0.05) suggesting protection from CI/R. A significantly reduced mean %necrotic flap area was not seen in either C1q KO or H2Bf KO mice relative to WT (22.9 and 31.3 vs. 43.1%; p=0.08 and p=0.244, respectively). There were no statistically significant differences between groups for markers of inflammation (TNFa, ICAM1, VCAM1, IL1b, IL6). In contrast, mRNA levels of IL10, a regulator of inflammation, were significantly increased in the MBL null group (p=0.047). Conclusions: We demonstrated for the first time a significant role of MBL and the lectin complement pathway in ischemia/reperfusion injury of the skin and a potential role for IL10 in attenuating CI/R injury, as IL10 levels were significantly increased in the tissue from the CI/R-protected MBL null group.