Leucocyte and Pathogen Trafficking through Lymphatics in Inflammation and Immunity

We are investigating how cells enter and move within lymphatic vessels so that in the future we can develop new therapies to block inflammation, prevent tumour spread, and make the delivery of vaccines to emerging infections more efficient. The lymphatic vessels form a dense network that intertwines the blood circulation and whose main functions are to maintain fluid balance and to transport cells carrying foreign antigen to the lymph nodes where they meet T and B cells and stimulate the immune response. Importantly, the lymphatics also contribute to diseases such as cancer by allowing metastatic tumours (e.g. skin and breast cancer) to spread to other parts of the body, and they act as a reservoir for malignant cells. Even though the involvement of lymphatics in disease have been known for a long time, their biology is still not well understood and so research in my group is dedicated to understanding how immune cells and tumours enter and navigate within the lymphatics. Thus far we have discovered that in inflammation, entry of immune cells carrying proteins from infectious agents depends critically on recognition of inflammation-induced protein receptors on the surface of lymphatic vessels, and that this is obligatory for the generation of the immune response to infection. We have also identified a separate mechanism that controls tumour cell entry to the lymphatics during lymph node metastasis in murine tumours and humans. We are also particularly interested in researching a molecule in lymphatics called LYVE-1 and we anticipate that further research in this area will reveal new ways to block inflammation, and to promote protective immunity to emerging infectious agents by enhancing vaccine delivery.

Goals To investigate mechanisms of lymphatic trafficking in inflammation, immunity and cancer. In addition to maintaining fluid balance and tissue homeostasis the lymphatics also provide a conduit for trafficking of antigen presenting cells to lymph nodes for activation of nave T cells, and in so doing they allow a route for tumour metastasis. Recent work has focused on understanding the key molecular mechanisms regulating entry of leukocytes and tumour cells to lymphatics and their subsequent trafficking to lymph nodes. We have discovered a separate new integrin and chemokine dependent pathway for translymphatic migration of dendritic cells (DC) that functions in inflammation (1) and demonstrated its importance for dermal antigen delivery during T cell responses - identifying a new potential target for intervention (2). We have focused on two lectin-like receptors of the Link superfamily, LYVE-1 and CD44. LYVE-1 is the major HA receptor of lymphatic endothelial cells and was originally cloned and characterized in my laboratory (3). We have shown that in addition to mediation of lymphatic trafficking of DC, LYVE-1 also plays a role in lymphatic invasion in tumour metastasis and in the resolution of inflammation in a model of acute lung injury. We have identified tumour lymphatic endotherlial cell markers (TLEM) and have shown these to be important in nodal metastasis in a range of murine and human cancers (4). The crystal structure and activation mechanism of CD44, an inflammatory leukocyte HA receptor closely related to LYVE-1 and which plays a pivotal role in transmigration of activated leukocytes across inflamed vascular endothelium have been determined (5). Future research plans Future work will concentrate on the definition of the lymphatic entry points and molecular mechanisms for transmigration of different leukocyte populations. The use of microscopic imaging and structure/function analyses will allow us to determine how receptors such as LYVE-1 mediate cell trafficking in animal models of inflammation. Moreover, we will pursue the 3D structure of the LYVE-1 ectodomain and elucidate the mechanisms regulating it's interaction with hyaluronan, search for additional LYVE-1 ligands mediating leukocyte trafficking, define downstream signalling pathways mediating transendothelial migration and investigate function blocking antibodies of potential therapeutic value for inflammation and cancer. References: (1) Johnson et al. 2006 J Exp Med 203: 2763; (2) Teoh et al. 2009 J Immunol 182: 2425; (3) Gale et al 2007 Mol Cell Biol 27: 595; (4) Clasper et al. 2008 Cancer Res 68:7293; (5) Banerji et al. 2007 Nature Struct Mol Biol 14:234