The effect of ozone exposure on the ability of human surfactant protein A variants to stimulate cytokine production

Abstract

Ozone exposure can cause inflammation and impaired lung function. Human surfactant protein A (SP-A) may play a role in inflammation by modulating cytokine production by macrophages. SP-A is encoded by two genes, SP-A1 and SP-A2, and several allelic variants have been characterized for each gene. These allelic variants differ among themselves in amino acids that may exhibit differential sensitivity to ozone-induced oxidation and this may produce functional differences. We studied the effects of SP-A variants before and after ozone exposure on the production of tumor necrosis factor (TNF)-α and interleukin (IL)-8. These are important proinflammatory cytokines and are expressed by the macrophage-like THP-1 cells. Eight variants were expressed in vitro, characterized by gel electrophoresis, and studied. These included six single-gene SP-A alleles and two SP-A variants derived from both genes. Variants were exposed to ozone at 1 ppm for 4 hr at 37°C, and we compared their ability to stimulate cytokine (TNF-α and IL-8) production by THP-1 cells to air-exposed and unexposed SP-A variants. We found that a) SP-A2 variants (1A, 1A0, 1A1) stimulate significantly more TNF-α and IL-8 production than SP-A1 variants (6A, 6A2, 6A4); b) coexpressed SP-A variants (1A0/6A2, 1A1/6A4) have significantly higher activity than single gene products; c) after ozone exposure, all SP-A variants showed a decreased ability to stimulate TNF-α and IL-8 production, and the level of the decrease varied among SP-A variants (26-48%); and d) human SP-A from patients with alveolar proteinosis exhibited a minimal decrease (18% and 12%, respectively) in its ability to stimulate TNF-α and IL-8 after in vitro ozone exposure. We conclude that biochemical and functional differences exist among SP-A variants, that ozone exposure modulates the ability of SP-A variants to stimulate cytokines by THP-1 cells, and that SP-As from bronchoalveolar lavage (BAL) fluid of certain alveolar proteinosis patients may be oxidized in vivo.