Role of gingival lymphatics in tissue fluid balance and periodontal disease development

Background: The gingiva is frequently challenged to oral bacteria which are able to induce inflammatory responses with increased fluid filtration and edema formation in the tissue. Under given circumstances periodontal pathogens can also promote periodontal disease characterized by bone resorption. Lymphatic vessels drain fluid from the interstitium and transport lymphocytes and antigen-presenting toward lymph nodes to elicit immune responses. In gingiva, lymphatic vessels are found, but their function in transcapillary fluid balance and their role in periodontal disease development was hitherto unknown. Methods and Results: We demonstrated that the mouse model of lymphedema, the K14-VEGF receptor 3-Ig (K14) mice, lacked gingival lymphatic vessels and had an almost absence of lymphatics in the mucosal layer of alveolar mucosa. We therefore used this transgenic mouse model to investigate the role of gingival lymphatics intranscapillary fluid balance in steady state situation and after perturbation of the tissue. The gingiva of K14 mice had significantly higher interstitial fluid pressure (Pif) in normal situation and after inflammation-induced by lipopolysaccharide (LPS) from Porphyromonas gingivalis (P. gingivalis) compared with wild type (WT) controls. Overhydration caused more than 75% increase in interstitial fluid volume (IFV) followed by a drop in Pif after recovery in both strains. Continuous measurements during the expansion showed an increase in Pif followed by a decline, suggesting that compliance is increased during edema formation. In the alveolar mucosa, no strain differences were observed in Pif and IFV in any situation, suggesting that mucosal lymphatics are not critical for tissue fluid regulation. Using WT mice, we further demonstrated that lymphatic growth take place in gingiva after P. gingivalis oral gavage. The lymphatics area fraction was increased in infected mice at both 10 and 42 days postinfection and modest bone loss was verified in the longest observation period, whereas proliferation of vessels was observed only in the shortest observation period. Higher numbers of immune cells expressing