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A5946 - Genetic Variation in Surfactant Protein-A2 Differentially Modulates Resolution of Eosinophilia During Allergic Airways Inflammation
Author Block: A. Dy, K. J. Addison, W. Pederson, M. Arif, M. Kraft, J. G. Ledford; Medicine, University of Arizona, Tucson, AZ, United States.
RATIONALE: Humans have two functional surfactant protein-A (SP-A) genes, SP-A1 and SP-A2, that together form complex oligomeric structures. While many genetic variants of SP-A exist, specific genetic variants of SP-A2 (rs1965708), corresponding to a Q (Gln) to K (Lys) amino acid substitution at position 223 of the lectin domain, have been associated with lower lung function in patients with asthma. Among a subgroup of asthmatics, eosinophilia is a well-documented phenotype, which is often accompanied by inflammation associated with delayed clearance. Our data in mice suggests that the major SP-A2 allele 223Q is more efficient at promoting eosinophil clearance after allergen challenge than the minor allele 223K. Therefore, we hypothesize that SP-A promotes resolution of allergic airway inflammation and that the Q223K polymorphism in the SP-A2 gene alters this activity.
METHODS: WT, SP-A-/- and humanized (SP-A2 223Q/Q, SP-A2 223K/K) mice were challenged in an allergic OVA model and parameters of inflammation were examined 24 hours and 5 days after the terminal challenge. Total and differential cell counts of bronchoalveolar lavage fluid were determined by Wright’s staining and cytokine levels were determined by ELISA. Eosinophils were isolated from the blood of IL-5 transgenic mice and stimulated with isolated human SP-A containing either 223Q/Q or 223Q/K at the position of interest in SP-A2. Chemoattractant ability was measured by migration assays using transwell tissue culture plates. Viability of eosinophils over time was assessed by Trypan Blue exclusion and caspase cleavage was determined by Western blotting.
RESULTS: One day post terminal challenge, SP-A-/- and SP-A2 223Q/Q have significantly increased BAL eosinophilia compared to SP-A2 223K/K mice. However, 5 days post challenge, SP-A-/- and humanized SP-A2 223K/K mice have enhanced BAL eosinophilia compared to WT and SP-A2 223Q/Q mice suggesting a delayed resolution phenotype. In vitro, human SP-A containing either the 223Q/Q or the 223K/K allele acted as a chemoattractant for eosinophils while stimulation with SP-A2 223Q/Q exhibited a significantly greater percentage of cell death and caspase cleavage compared to SP-A2 223Q/K.
CONCLUSION: Our results suggest that SP-A plays a role in the resolution of allergic airway inflammation through mediation of eosinophil clearance from the lung tissue by 1) directly promoting chemotaxis which is not affected by position SP-A2 Q223K and 2) aiding in apoptosis of eosinophils in the lumen which is affected by the polymorphism at position SP-A2 Q223K.