Surfactant Protein-A Regulation of Innate Immunityin Asthma

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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 isolated 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.