Antigen-induced generation of lyso-phospholipids in human airways

The goal of the current study was to examine the formation of phospholipids, 1-radyl-2-lyso-sn-glycero-phospholipids (lyso-PL) and 2- acetylated phospholipids (such as PAF) as well as mechanisms responsible for generating these phospholipids m bronchoalveolar lavage fluid (BALF) from allergic subjects challenged with antigen. Bronchoalveolar lavage was performed in normal and allergic subjects before, 5-30 min, 6 h, and 20 h after segmental antigen challenge via a wedged bronchoscope. Levels of 1- hexadecyl-2-lyso-phospholipids and 1-hexadecyl-2-acetyl-phospholipids were initially determined by negative ion chemical ionization gas chromatography/mass spectrometry (NICI-GC/MS). Antigen dramatically elevated quantities of 1-hexadecyl-2-lyso-phospholipids in allergic subjects 20 h after challenge when compared to non-allergic controls. In contrast, there was not a significant increase in levels of 1-Hexadecyl-2-acetyl phospholipids after antigen challenge. Closer examination of 1-radyl-2-lyso- sn-glycero-3-phosphocholine (GPC) revealed that 1-palmitoyl-2-lyso-GPC 1- myristoyl-2-lyso-GPC and 1-hexadecyl-2-lyso-GPC were three major molecular species produced after antigen challenge. 1-palmitoyl-2-lyso-GPC increased sevenfold to levels of 222 ± 75 ng/ml of BALF 20 h after antigen challenge. The elevated levels of lyso-PL correlated with levels of albumin used to assess plasma exudation induced by allergen challenge. In contrast, the time course of prostaglandin D₂ (PGD₂) or 9α, 11βPGF₂ (11βPGF₂) formation did not correlate with lyso-PL generation. To examine the mechanism leading to lyso-phospholipid formation m antigen-challenged allergic subjects, secretory phospholipase A₂ (PLA₂) and acetyl hydrolase activities were measured. There was a significant increase in PLA₂ activity found in BALF of allergic subjects challenged with antigen when compared to saline controls. This activity was neutralized by an antibody directed against low molecular mass, (14 kD) human synovial PLA₂ and dithiothreitol. Acetyl hydrolase activity also markedly increased m BALF obtained after antigen challenge. This study indicates that high levels of lyso-PLs are present in airways of allergic subjects challenged with antigen and provides evidence for two distinct mechanisms that could induce lyso-PL formation. Future studies will be necessary to determine the ramifications of these high levels of lyso- phospholipids on airway function.