Mechanisms of leucocyte migration via the lymphatics in immunity and inflammation

Fundamental to generating a host immune response to infection is the mobilisation of antigen loaded dendritic cells (DCs) in the affected tissues and their migration via afferent lymph to draining nodes where they prime and activate T cells in the paracortex. The trafficking of DCs through afferent lymphatic vessels is vital to such immunity, and involves a series of co-ordinated steps driven by chemokines, including CCL21 and CX3CL1 secreted from initial lymphatic capillaries and supported by a plethora of adhesion receptors (see Fig 1) whose expression is frequently upregulated during inflammation.

Besides DCs, other leucocyte populations such as macrophages and neutrophils also migrate through lymphatics, and such migration is important for their clearance from the tissues during the resolution of inflammation. The precise choreography of directional guidance, endothelial adhesion and transmigration, and downstream trafficking to lymph nodes are however unclear. Most leucocytes are thought to access lymphatic capillaries in the tissues at specialised overlapping junctions, distinct from the tight junctions of blood capillaries. Here, the flap-like edges of oakleaf shaped endothelial cells interdigitate to form button-like portals, whose tips are decorated with the lymphatic vessel specific hyaluronan receptor LYVE-1 (reviewed in Jackson 2014), and whose sides are pinned by adherens and tight junction receptors VE- cadherin, claudins and JAMs (Fig 2). The implication is that engagement of migrating cells with these portals leads to loosening of the junctions and entry to the vessel lumen (Fig 3). Recent work in my laboratory using a combination of in vitro and in vivo approaches has yielded compelling evidence that DCs initially adhere to lymphatic endothelium via LYVE-1, and that the interaction involves reversible avidity-dependent binding to hyaluronan arranged appropriately within the DC surface glycocalyx (Lawrance et al 2016; Johnson et al 2017), thus enabling the migrating cells to dock via transmigratory cups and transit to the vessel lumen. An analogous mechanism appears to mediate systemic spread of virulent strains of Group A streptococci, the agents of bacterial tonsillitis and necrotizing fasciitis, whose dense hyaluronan capsule mediates both lymphatic tropism and protection against host phagocytosis (Lynskey et al. 2015). Ongoing work suggests that monocyte/macrophages may also utilize LYVE-1 to navigate the lymphatics, during the course of tissue inflammation. How LYVE-1 selectively binds The project on offer will provide an exciting opportunity to explore the in vivo anatomy of LYVE-1 mediated leucocyte interactions during leucocyte trafficking in more detail, using intravital video microscopic imaging as well as in vitro analytical approaches. Questions to be addressed may include the following -
◾How does the LYVE-1:HA axis integrate with chemotaxis for vessel entry ?
◾Are LYVE-1:HA interactions involved primarily in leucocyte docking or do they also assist in DC crawling within the vessel lumen ?
◾Do they also mediate subsequent interactions with the subcapsular cortical or medullary sinuses in downstream lymph nodes ?

The successful candidate will have the benefit of supervision both from the PI, and from a dedicated senior research scientist, as well as close Unit support and international collaborations with other leading scientists in the field. We anticipate the new insights gained in these preclinical studies to seed future development of novel therapeutic strategies for inflammatory diseases. The work will involve the use of animal models of inflammation, ex vivo tissue explants and in vitro culture models to visualize, characterise, manipulate and quantify leucocyte trafficking, hyaluronan glycocalyx/complex formation and tissue vasculature by confocal and intravital imaging. Experiments will take advantage of constitutive and conditional LYVE-1-/- mice, LYVE-1 function blocking mAbs and appropriate fluorescent reporter mice that will be available in the host laboratory.

The successful candidate will receive training in flow cytometry, confocal/intravital microscopy, endothelial cell culture and characterization, ex vivo/in vitro transmigration assays, in vivo studies in animal inflammatory disease models, immunoassays, molecular biology techniques and protein analysis.The host Institute, and the MRC Human Immunology Unit have world class, cutting edge facilities for microscopic imaging, including super-resolution (STED) microscopy and a dedicated suite for intravital imaging.

As well as the specific training detailed above, students will have access to a wide-range of seminars and training opportunities through the many research institutes and centres based in Oxford, including the Methods and Techniques course run by the MRC Weatherall Institute of Molecular Medicine.

Generic skills training is offered through the Medical Sciences Division’s Skills Training Programme. The Department has a successful mentoring scheme, open to graduate students. We hold an Athena SWAN Silver Award in recognition of our efforts to support the careers of female students and staff.