Lymphatic trafficking of immune cells and insights for cancer metastasis.

Most cancers and in particular carcinomas metastasise via the lymphatics to draining lymph nodes from where they can potentially achieve systemic dissemination by invasion of high endothelial blood venules (HEVs) in the paracortex [1, 2]. Currently however, the mechanisms by which tumours invade and migrate within the lymphatics are incompletely understood, although it seems likely they exploit at least some of the normal physiological mechanisms used by immune cells to access lymphatic capillaries and traffic to draining lymph nodes in the course of immune surveillance, immune modulation and the resolution of inflammation [3, 4]. Typically these include directional guidance via chemotaxis, haptotaxis and durotaxis, adhesion to the vessel surface via receptors including integrins, and junctional re-modelling by MMPs (Matrix MetalloProteinases) and ADAMs (A Disintegrin And Metalloproteinases) [5-7]. This short review focusses on a newly emerging mechanism for lymphatic entry that involves the large polysaccharide hyaluronan (HA) and its key lymphatic and immune cell receptors respectively LYVE-1 (Lymphatic Vessel Endothelial receptor) and CD44, and outlines recent work which indicates this axis may also be used by some tumours to aid nodal metastasis.