Browsing by Author "Wright, Jo Rae"

Concurrent with the global escalation of the AIDS pandemic, cryptococcal infections are increasing and are of significant medical importance. Although improvements in antifungal therapy have advanced the treatment of cryptococcosis, the mortality rate is approximately 12% in medically advanced countries, and approaches 50% in less developed regions. Additionally, C. neoformans can cause infection in seemingly healthy individuals, elevating its status as a primary human pathogen. Although numerous studies have examined virulence properties, less is understood regarding host immune factors in the lungs during early stages of fungal infection. In the present thesis studies, I examined the roles played by pulmonary surfactant proteins in response to C. neoformans in vitro and in vivo. We demonstrate that SP-D, but not SP-A, binds to the yeast and increases phagocytosis of poorly encapsulated yeast cells by macrophages, yet concomitantly protects the pathogenic microbes from macrophage-mediated defense mechanisms. Furthermore, we show that SP-D functions as risk factor in vivo by protecting the yeast cells against oxidant species and thus facilitating disease progression. The results of these studies provide a new paradigm on the role played by surfactant protein D during host responses to C. neoformans and, consequently, impart insight into potential future treatment strategies for cryptococcosis.

Due to its nature and function, the lungs are confronted with the unique challenge of rapidly eliminating inhaled pathogens and particulates while limiting inflammatory responses. A disruption in this immune homeostasis may result in respiratory inflammatory diseases, such as allergies or asthma. The alveolar epithelial type II cell and its secretory product, surfactant protein A (SP-A), have been linked to roles in adaptive immunity in the lung. The discovery that type II cells constitutively express major histocompatibility complex class II (MHC II) suggested that type II cells may function to present antigen to T cells. Studies in vitro demonstrated that SP-A inhibits the maturation of bone marrow-derived dendritic cells. The goal of this work was to determine how type II cells and SP-A may be functioning to regulate adaptive immunity in the lungs. The hypothesis tested is that type II cells and SP-A suppress the activity of T cells and dendritic cells in the lungs. As T cells and dendritic cells are critical for the initiation and function of the adaptive immune response, the inhibition of T cell and dendritic cell activity would limit inflammation in the lungs. Although isolated murine type II cells expressed MHC II, they did not express detectable levels of the costimulatory molecules CD80 and CD86 and were poor activators of T cells. Upregulation of MHC II on type II cells by interferon-gamma stimulation did not enhance the ability of type II cells to activate T cells. Instead, the type II cells suppressed T cells from subsequent activation to antigen in an antigen-dependent manner, indicative of tolerance. T cells pre-incubated with type II cells and antigen were suppressed from further activation, even after removal of the type II cells. Using a model of pulmonary infection with Mycoplasma pneumoniae, wildtype mice were found to have fewer mature dendritic cells in the mediastinal lymph nodes than SP-A null mice. The presence of SP-A in the wild-type mice had a suppressive effect on the M. pneumoniae-induced maturation of dendritic cells in the lungs. Together, the data demonstrate that type II cells and SP-A participate in the adaptive immune response by suppressing the activity of T cells and dendritic cells in the lungs.

The lung is a unique organ, taking a key part physiology but also playing a vital role in host defense. The lung has therefore developed a complex innate immune system that includes ciliated mucus producing cells that trap and remove larger particles in the larger airways and a specialized set of immune cells in the smaller airways. In addition, a variety of host proteins play a vital role in the immune response in the lung. The structural protein caveolin-1 (cav-1) is known to play a role in the uptake of pathogens and controls a variety of signaling pathways, although less is known about its functions in the lung. Surfactant protein A (SP-A) is a secreted protein that is vital in the innate immune response by interacting with microbes and immune cells. The goal of this work was to further elucidate the specific mechanisms by which cav-1 and SP-A affect the host responses, including inflammation and airway hyperreactivity (AHR), to pathogens and particulates. Using a mouse model of environmental lung injury I show that cav-1 is vital in the host response to inhaled lipopolysaccharide (LPS). Although the cav-1 deficient mice had greater lung inflammatory indices compared to wild-type mice, they exhibited reduced AHR following LPS exposure. The uncoupling of these two parameters led me to investigate the role of cav-1 in the contraction of airway smooth muscle and production of nitric oxide, both of which are known to regulate AHR. The bronchi of cav-1 deficient mice contract less than those from wild-type mice although their structure and receptor independent responses were not altered. The absence of cav-1 also resulted in increased nitric oxide levels in the lavage fluid and increased inducible nitric oxide synthase expression in the lung tissue. Administration of the potent and specific inhibitor 1400W increased AHR to levels comparable to wild-type mice. Following intranasal infection with Mycoplasma pneumoniae mast cell numbers increase in the lungs of mice and AHR is dramatically attenuated in SP-A-/- mice when mast cells are absent. Using SP-A-/- KitW-sh/W-sh mice engrafted with TNF-alpha-/- or TNF receptor (TNF-R-/-) mast cells, I find that TNF-alpha activation of mast cells via the TNF-R and not mast cell derived TNF-alpha, leads to augmented AHR during Mp infection. Additionally, Mp infected SP-A-/-KitW-sh/W-sh mice engrafted with TNF-alpha -/- or TNF-R-/- mast cells have decreased mucus production compared to those engrafted with wild-type mast cells, while burden was unaffected. Together, these data help to further elucidate the role of cav-1 and SP-A in innate immunity and may lead to the development of more effective human therapies.