Rapid Lymphatic Dissemination of Encapsulated Group A Streptococci via Lymphatic Vessel Endothelial Receptor-1 Interaction

The host lymphatic network represents an important conduit for pathogen dissemination. Indeed, the lethal human pathogen group A streptococcus has a predilection to induce pathology in the lymphatic system and draining lymph nodes, however the underlying basis and subsequent consequences for disease outcome are currently unknown. Here we report that the hyaluronan capsule of group A streptococci is a crucial virulence determinant for lymphatic tropism in vivo, and further, we identify the lymphatic vessel endothelial receptor-1 as the critical host receptor for capsular hyaluronan in the lymphatic system. Interference with this interaction in vivo impeded bacterial dissemination to local draining lymph nodes and, in the case of a hyper-encapsulated M18 strain, redirected streptococcal entry into the blood circulation, suggesting a pivotal role in the manifestation of streptococcal infections. Our results reveal a novel function for bacterial capsular polysaccharide in directing lymphatic tropism, with potential implications for disease pathology.
Author Summary Pathogens are known to invade the host not only via the systemic circulation but also via the lymphatic network, however the mechanisms underlying the latter route and the consequences for disease outcome have not been well studied. The important human pathogen, group A streptococcus, is responsible for a number of clinical syndromes affecting both the lymphatic vessels and draining lymph nodes, such as lymphangitis and lymphadenitis. How such pathologies are orchestrated, and their significance in the development of serious infection are currently unknown. In this study, we show that the hyaluronan capsule secreted by group A streptococcus is critical for bacterial spread to draining lymph nodes, and we demonstrate that this occurs as a result of a specific interaction with the lymphatic vessel endothelial receptor-1. Genetic deletion or functional blockade of this receptor prevented streptococcal transit to draining lymph nodes in a murine model of infection, which in turn enhanced bacterial spread into the blood circulation. Together these results define a novel interaction between the group A streptococcal capsule and the lymphatic endothelial receptor-1 as a critical axis in the establishment of lymphatic tropism for this pathogen, with clear implications for disease severity in the host.