SP-A as an immune modulator

Duke University, Durham NC

Investigators

Linked publications & trials

Abstract

DESCRIPTION (provided by applicant): The fundamental roles of innate and adaptive host responses are to recognize and eradicate invading antigens, pathogens or altered self components to restore tissue integrity and homeostasis. While resolution can occur when the host response is normal, an exogenous insult cannot be contained when a critical host factor is inactivated, dysregulated, or genetic and/or environmental factors conspire to result in chronic lung disease. In our proposal, this critical host factor is surfactant protein A (SP-A), a protein that lines the epithelial surfaces in the lung. Normal SP-A can attenuate allergic inflammation, but SP-A that is altered or abnormal as a consequence of genetic polymorphisms and/or oxidative changes has abrogated ability to defend the host from environmental insults leading to excessive bronchoconstriction and allergic inflammation. Our preliminary studies in vitro, in animal models of airway inflammation and in patients with asthma have identified specific defects in the role of SP-A in the innate immune response that contribute to the persistence or exacerbation of asthma and allergic disease. The central hypothesis to be tested is that SP-A, which normally regulates innate immunity and protects the host from persistence and exacerbation of asthma, is dysfunctional in asthma. These projects will employ specific environmental challenges (infection and ozone exposure) to test the ability of SP-A to modulate allergic inflammation in asthma, and whether allelic variants of SP-A, insufficient quantities or oxidation are responsible for dysfunction of SP-A in asthma. Project 1 will evaluate the ability of human SP-A from asthmatic subjects and allelic variant SP-A to modulate the innate and adaptive responses to infection and ozone exposure, respectively, in the human macrophage and airway epithelial cell. Project 2 will employ murine models of ovalbumin sensitization and challenge to determine if asthmatic SP-A and allelic variants of SP-A effectively modulate inflammaton induced by an infectious challenge. Project 3 will determine whether a specific SP-A polymorphisms modulate differential sensitivity to ozone exposure in asthma (physiologic and mechanical), and whether SP-A itself undergoes oxidation during in vivo ozone exposure in human asthma. We present three interrelated projects employing animal models and translational studies in humans that will determine how SP-A bridges the innate and adaptive immune systems in the host response to exogenous insults in asthma. We bring together our team of investigators with expertise in murine, biochemical and translational studies;our collective expertise and the synergy among projects will enable progress and high potential for success in the elucidation of SP-A-mediated host defense mechanisms critical to innate immune modulation of allergic inflammation in asthma. Project 1 - Surfactant Protein-A Regulation of Innate Immunity in Asthma (Kraft, M) PROJECT 1 DESCRIPTION (provided by applicant): Environmental agents, including the atypical bacteria, Mycoplasma pneumoniae, and ozone are known to contribute to the exacerbation of asthma. A first line of defense against inhaled challenges is the pulmonary innate immune system, which includes the surfactant proteins. We have demonstrated that SP-A binds to lipids and proteins on M. pneumoniae, a TLR2 agonist, attenuating its pathogenicity. This line of defense may be particularly important in asthma, as studies have shown that SP-A inhibits allergen-induced lymphocyte proliferation and histamine release by immune cells from asthmatic children. SP-A null mice exhibit increased susceptibility to infection and inflammation caused by bacteria and viruses, and exhibit enhanced allergic inflammation. SP-A alleles have been associated with a variety of lung diseases including oxidant injury associated with ozone exposure and a recent association with increased risk for asthma. These data imply that disease susceptibility may be associated with variants of SP-A that have altered host defense functions and offer reduced protection in the setting of environmental insults. Therefore, surfactant proteins may have multiple roles in attenuating infection and inflammation. We hypothesize that in asthma, dysfunction of SP-A, due to quantitative and functional deficiencies in the protein, is associated with reduced ability to modulate inflammation. This dysfunction results in increased allergic inflammation in asthma. We propose that the basis of dysfunction is both genetic and structural. In Aim 1, we will determine the relationship between the genotypes at the SP-A loci and the actual proteins expressed in the bronchoalveolar compartments of normal and asthmatic individuals employing a proteonomics approach. In aim 2, we will determine the activity of SP-A isolated from normal and asthmatic subjects and specific SP-A allelic variants in the recognition of Mycoplasma pneumoniae, and the modulation of the innate immune response of human macrophages. In specific aim 3, we will determine the activity of specific SP-A allelic variants and SP-A isolate from normal and asthmatic subjects in modulation of the immune response by airway epithelial cells to the environmental insults M. pneumoniae and ozone exposure, respectively. This project is an integral part of the global goal of this program: to determine how SP-A modulates response to environmental insults that result in allergic airway inflammation. Project 1 will interface closely with Project 2 (Dr. Wright), as these concepts will be investigated in human and animal models of disease. Project 1 will also interface closely with Project 3 (Dr. Foster) as bronchoalveolar lavage (BAL) obtained from subjects recruited in Project 3 will be studied in Dr. Kraft's laboratory in Project 1. All projects will share a Clinical and Laboratory Core, which Drs. Sundy, Voelker and Kraft will co-direct.