The lymphatic system provides a conduit for the trafficking of immune cells from the periphery to draining lymph nodes, both for constitutive immune surveillance and during inflammation. Thus, leucocyte migration into the lymphatics represents an important step in the initiation of a primary immune response, which occurs within lymph nodes. Traditionally, it has been considered that neutrophils are absent from the afferent lymph, having a finite lifespan in the periphery after extravasation from the blood. However, recent research has reported the presence of neutrophils in lymph nodes, in animal models of infection, where neutrophil trafficking was found to occur through afferent lymphatic vessels. This thesis examines the mechanisms regulating neutrophil migration, both by the lymphatic endothelium and neutrophils themselves, under resting and inflammatory conditions. Primary human dermal lymphatic endothelial cells (HDLECs) respond to the pro- inflammatory cytokine, TNF-α by instigating a distinct expression programme, characterised by the up-regulation of various adhesion molecules (ICAM-1, VCAM-1, E-selectin), and CXC- chemokines (ENA-78, GROβ, IL-8), as well as other potential regulators of neutrophil entry such as constitutively expressed adhesion molecules, CD99 and ESAM. Moreover, neutrophils possess counter-receptors for these adhesion molecules and contain basement membrane-specific proteases (elastase) and matrix metalloproteinases (MMPs) such as MMPs -8 and -9, localised in intracellular granules, ready to be exocytosed upon inflammatory stimuli. In vitro data presented in this thesis demonstrate that neutrophil adhesion and transmigration of the lymphatic endothelium is entirely dependent on prior activation of the monolayer with TNF-a. Furthermore, the aforementioned lymphatic-expressed adhesion molecules and chemokines, as well as neutrophil-derived proteases and MMPs are shown to play critical roles in neutrophil adhesion and transmigration of the lymphatic endothelium. Subsequent in vivo experiments confirmed that neutrophil trafficking to lymph nodes across lymphatic vessels is wholly dependent on prior vaccination with Mycobacterium bovis Bacillus Calmette-Guerin (BCG) Tokyo-172. Moreover, neutrophils trafficking to lymph nodes across lymphatic vessels are shown to require ICAM-1. The results described in this thesis provide the first evidence that both the lymphatic endothelium and neutrophils act in concert to regulate entry to lymph nodes and determine the outcome of infection, or vaccination.

Indiana University-Purdue University Indianapolis (IUPUI) / More than 300 million people world-wide suffer from breathlessness, wheezing, chest tightness, and coughing characteristic of chronic bronchial asthma, the global incidence of which is on the rise. Allergen-sensitization and challenge elicits pulmonary expression of chemoattractants that promote a chronic eosinophil-rich infiltrate. Eosinophils are increasingly recognized as important myeloid effectors in chronic inflammation characteristic of asthma, although few eosinophil molecular signaling pathways have successfully been targeted in asthma therapy. p21 activated kinases (PAKs), members of the Ste-20 family of serine/threonine kinases, act as molecular switches in cytoskeletal-dependent processes involved in cellular motility. We hypothesized that PAK1 modulated eosinophil infiltration in an allergic airway disease (AAD) murine model. In this model, Pak1 deficient mice developed reduced inflammatory AAD responses in vivo with notable decreases in eosinophil infiltration in the lungs and broncho-alveolar lavage fluids (BALF). To test the importance of PAK1 in hematopoietic cells in AAD we used complementary bone marrow transplant experiments that demonstrated decreased eosinophil inflammation in hosts transplanted with Pak1 deficient bone marrow. In in vitro studies, we show that eotaxin-signaling through PAK1 facilitated eotaxin-mediated eosinophil migration. Ablating PAK1 expression by genetic deletion in hematopoietic progenitors or siRNA treatment in derived human eosinophils impaired eotaxin-mediated eosinophil migration, while ectopic PAK1 expression promoted this migration. Together these data suggest a key role for PAK1 in the development of atopic eosinophil inflammation and eotaxin-mediated eosinophil migration.