Lymphatics and inflammation

Inflammation is a local or systemic tissue reaction caused by external or internal stimuli with the objective to remove the noxa, inhibit its further dissemination and eventually repair damaged tissue. Blood vessels and perivascular connective tissue are important regulators of the inflammatory process. After a short initial ischemic phase, inflamed tissue is characterized by hyperaemia and increased permeability of capillaries. Therefore, blood vessels have been in the focus of inflammation research for quite some time, whereas lymphatic vessels have been neglected. Their reactivity is not immediately obvious, and, their identification within the tissue has hardly been possible until lymphatic endothelial cell (LEC)-specific molecules have been identified a few years ago. This has opened up the possibility to study lymphatics in normal and diseased tissues, and to isolate LECs for transcriptome and proteome analyses. Initial studies now provide evidence that lymphatics are not just a passive route for circulating lymphocytes, but seem to be directly involved in both the induction and the resolution of inflammation. This review provides a summary on the basics of inflammation, the structure of lymphatics and their molecular markers, human inflammation-associated diseases and their relation to lymphatics, animal models to study the interaction of lymphatics and inflammation, and finally inflammation-associated molecules expressed in LECs. The integration of lymphatics into inflammation research opens up an exciting new field with great clinical potential.