Mesenteric Lymph Derived from Ischemia/Reperfusion Gut Promotes Neutrophil Activation and Lung Infiltration

Abstract

Intestinal ischemia/reperfusion (I/R) can induce systemic inflammation and remote organ injury, where cytokine production and bacteria translocation are traditionally thought to be the major underlying mechanisms. The objective of our study was to determine whether the lymphatic circulation participates in this process. We focused on mesenteric lymph duct, as it drains gut interstitial fluid, proteins, absorbed lipids, and immune cells into the blood circulation through subclavian vein; the lungs are the first organ directly exposed to lymph contents. In a mouse model of intestinal I/R, we found that I/R‐induced lung inflammation, as evidenced by neutrophil infiltration and myeloperoxidase production, was inhibited by mesenteric lymph duct ligation. We then compared the direct effects of lymph collected from pre‐I/R vs. post‐I/R mesenteric lymph duct on isolated neutrophils from normal animals. Flow cytometric analysis revealed that neutrophils treated with post‐I/R lymph exhibited increased surface expression of CD11b. Additionally, upregulated mRNA expression of neutrophil specific chemokines (e.g. Cxcl1, Cxcl2, and Cxcl5) and pro‐inflammatory markers (e.g. Il1b, Il6, and Tnfa) was detected in post‐I/R lymph‐treated neutrophils. These effects were not seen in neutrophils treated with pre‐I/R lymph. Furthermore, because intestinal I/R injury is known to be associated with gut barrier leakage and bacteria translocation into the blood, we thought to determine whether bacteria translocation occurred to the lymphatic circulation during I/R. However, PCR experiments confirmed that all lymph samples tested, regardless of I/R status, were free of bacterial 16s rRNA, excluding the direct involvement of gut bacteria in I/R lymph‐induced neutrophil activation. In conclusion, our study suggests that mesenteric lymph derived from I/R gut contributes to systemic and lung inflammation by activating neutrophils. Support or Funding Information The work is supported by the American Heart Association 15SDG22930009 (to YM) and by the National Institutes of Health HL070752 (to SYY).