Thoracic Duct Lymph Suppresses Macrophage Activation after Stimulation with Lipotheichoic Acid

Purpose: Streptococcus pneumoniae is a gram positive bacterium that is a major cause of community acquired pneumonia. Lipoteichoic acid (LTA) can be found on the outermost surface of gram positive bacteria, including S. pneumoniae. These bacterial components activate macrophages to release pro-inflammatory substances, such as nitric oxide (NO), which can cause oxidative damages to bacteria. Tumor necrosis factor alpha (TNFα) is a cytokine involved in cell signaling pathways as part of the immune response. In recent studies, osteopathic manipulative therapy (OMT) was shown to protect against acute pneumonia. Our lab has demonstrated that osteopathic lymphatic pump technique (LPT) enhanced the flux of cytokines, reactive oxygen and nitrogen species in thoracic and mesenteric lymph. By enhancing lymph flow, LPT may boost the innate immune response against pneumonia. In this study, we hypothesized that factors in lymph would stimulate macrophage activity Methods: To test this hypothesis, thoracic duct lymph (TDL) was collected from 8 dogs before, during and after OMT sessions using the lymphatic pump technique (LPT). These lymphatic pools were labeled as baseline TDL, LPT TDL, and recovery TDL, respectively. In addition, a mouse alveolar macrophage cell line (MH-S) was used for this in vitro study. Phosphate-buffered saline (PBS), baseline TDL, LPT TDL and recovery TDL were added at 5% total volume per well. To activate macrophages LTA (100 micrograms) were added for 24 hours. The concentration of nitrite and TNF-α using were measured in culture supernatants. Results: TDL had no effect on macrophages cultured without LTA. Following activation with LTA baseline, LPT and recovery TDL suppressed the production of NO (33%, 21% and 19% decrease, respectively) and TNFα (75%, 75% and 80% decrease, respectively) compared to macrophages cultured with 5% PBS. Conclusions: Our results suggest that lymph suppress LTA-induced activation of alveolar macrophages. One explanation is that in healthy individuals, the gastrointestinal environment is normally immune suppressive. During OMT, these anti-inflammatory substances may be mobilized to target tissue via the lymphatic system.