Differential Effects of Thoracic Duct Lymph on Pulmonary Macrophages




Conway, Allison
Castillo, Rudy A.
Hodge, Lisa


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Purpose: The gut-lung axis remains a poorly defined mechanism that could impact etiology and treatment of gut and respiratory diseases. Early literature first described this gut-lung crosstalk in inflammatory bowel disease patients with chronic bronchopulmonary disease. Recent literature describes the role of intestinal lymph during acute respiratory distress syndrome (ARDS). In these studies, intestinal ischemia and reperfusion injury in animal models induces lung injury suggesting factors, such as cytokines and lipids, released from the gut during gastrointestinal shock can contribute to ARDS. The gut lymphatics provide a large pool of lymph rich in immune cells, inflammatory mediators, and lipids. Our lab has previously demonstrated lymph-enhancing techniques enhanced the flux of cytokines, chemokines and reactive oxygen and nitrogen species in thoracic and mesenteric lymph. We propose factors released from the gut travel through the lymphatics to the lung and suppress the immune response in the lung. Methods: To test this hypothesis, alveolar macrophages from bronchoalveolar lavage fluid (BALF), lung tissue macrophages (after BALF collected) and intraperitoneal (IP) macrophages from IP lavage were isolated from healthy F344 rats. In addition, a rat alveolar macrophage cell line (NR8383) was used for in vitro studies. Macrophages were cultured for 12 hours and canine thoracic duct lymph (TDL) at 10% total volume per well and/or LPS (500ng per well) added for 24 hours. Supernatants were stored and used to measure nitric oxide (NO) and tumor necrosis factor alpha (TNFa) using Griess assay and ELISA. Results: AM were the most sensitive to LPS activation compared to LM and IP macrophages. TDL suppressed LPS-induced NO (52% decrease) and TNFa (25% decrease) production. However, TDL did not significantly suppress LPS activation in LM and IP macrophages. In NR8383, TDL suppressed LPS-induced NO (86% decrease) and TNFa (66% decrease) production. TDL alone did not activate NR8383, AM, LM or IP macrophages and did not affect cell viability after culture. Conclusions: Our results suggest a biological factor in lymph selectively suppresses LPS activation in alveolar macrophages. The mobilization of healthy lymph may protect the lung from chronic inflammation caused by pathogens and pulmonary disease. Future studies will focus on identifying factors in lymph that may modulate the immune response that may improve disease outcome.