Impaired meningeal lymphatic drainage in Listeria monocytogenes infection

Previous studies have demonstrated an association between lymphatic vessels and diseases caused by bacterial infections. Listeria monocytogenes (LM) bacterial infection can affect multiple organs, including the intestine, brain, liver and spleen, which can be fatal. However, the impacts of LM infection on morphological and functional changes of lymphatic vessels remain unexplored. In this study, we found that LM infection not only induces meningeal and mesenteric lymphangiogenesis in mice, but also impairs meningeal lymphatic vessels (MLVs)-mediated macromolecules drainage. Interestingly, we found that the genes associated with lymphatic vessel development and function, such as Gata2 and Foxc2, were downregulated, suggesting that LM infection may affect cellular polarization and valve development. On the other hand, photodynamic ablation of MLVs exacerbated inflammation and bacterial load in the brain of mice with LM infection. Overall, our findings indicate that LM infection induces lymphangiogenesis and may affect cell polarization, cavity formation, and valve development during lymphangiogenesis, ultimately impairing MLVs drainage.

Intestinal inflammations increase efflux of innate lymphoid cells from the intestinal mucosa to the mesenteric lymph nodes through lymph-collecting ducts

INTRODUCTION

Innate lymphoid cells (ILCs) are abundant in the intestinal mucosa, forming boundaries externally. Herein, ILCs were directly obtained from intestinal lymph using a lymph fistula rat model and analyzed under physiological and pathological conditions.

METHODS

Thoracic duct (TD) lymphocytes were collected by cannulation with/without preceded mesenteric lymphadenectomy, which were comparable to lymphocytes flowing through mesenteric lymphatic vessels (MLVs) or TD, respectively. The collected ILCs were classified according to gene transcription factors and analyzed by flow cytometry. The effect of IL-25 or indomethacin was studied.

RESULTS

The proportion of total ILCs in the MLVs (MLV-ILCs) was significantly higher than that in TD (TD-ILCs, 0.01% vs. 0.003%, respectively). Physiologically, there were several significant differences in the MLV-ILCs compared with TD-ILCs, including the proportion of ILC2 (42.3% vs. 70.9%) and ILC3 (33.3% vs. 13.8%), and the proportion of α4-integrin-positive cells (36.8% vs. 0.3%). IL-25 significantly increased the proportion of MLV-ILC2 after 3 days. Indomethacin-induced intestinal injury increased the proportion of MLV-ILC3 in the early phase within 12 h.

CONCLUSION

Intestinal ILCs were found to migrate through MLVs. The altered mobilization of MLV-ILCs after stimuli suggests that ILCs play an important role in regulating the immune responses at the secondary lymph nodes.

Histamine as an Endothelium-Derived Relaxing Factor in Aged Mesenteric Lymphatic Vessels

BACKGROUND

Knowledge of the mechanisms by which aging affects contracting lymphatic vessels remains incomplete; therefore, the functional role of histamine in the reaction of aged lymphatic vessels to increases in flow remains unknown.

METHODS AND RESULTS

We measured and analyzed parameters of lymphatic contractility in isolated and pressurized rat mesenteric lymphatic vessels (MLVs) obtained from 9- and 24-month Fischer-344 rats under control conditions and after pharmacological blockade of nitric oxide (NO) by Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 100 μM) or/and blockade of histamine production by α-methyl-DL-histidine dihydrochloride (α-MHD, 10 μM). We also quantitatively compared results of immunohistochemical labeling of the histamine-producing enzyme, histidine decarboxylase (HDC) in adult and aged MLVs. Our data provide the first demonstration of an increased functional role of histamine as an endothelial-derived relaxing factor in aged MLVs, which appears in parallel with the abolished role of NO in the reactions of these lymph vessels to increases in flow. In addition, we found an increased expression of HDC in endothelium of aged MLVs.

CONCLUSIONS

Our findings provide the basis for better understanding of the processes of aging in lymphatic vessels and for setting new important directions for investigations of the aging-associated disturbances in lymph flow and the immune response.

Involvement of histamine in endothelium-dependent relaxation of mesenteric lymphatic vessels

OBJECTIVES

The knowledge of the basic principles of lymphatic function, still remains, to a large degree, rudimentary and will require significant research efforts. Recent studies of the physiology of the MLVs suggested the presence of an EDRF other than NO. In this study, we tested the hypothesis that lymphatic endothelium-derived histamine relaxes MLVs.

METHODS

We measured and analyzed parameters of lymphatic contractility in isolated and pressurized rat MLVs under control conditions and after pharmacological blockade of NO by L-NAME (100 μM) or/and histamine production by α-MHD (10 μM). Effectiveness of α-MHD was confirmed immunohistochemically. We also used immunohistochemical labeling and Western blot analysis of the histamine-producing enzyme, HDC. In addition, we blocked HDC protein expression in MLVs by transient transfection with vivo-morpholino oligos.

RESULTS

We found that only combined pharmacological blockade of NO and histamine production completely eliminates flow-dependent relaxation of lymphatic vessels, thus confirming a role for histamine as an EDRF in MLVs. We also confirmed the presence of HDC and histamine inside lymphatic endothelial cells.

CONCLUSIONS

This study supports a role for histamine as an EDRF in MLVs.