Secretory phospholipase A2 activity is elevated in bronchoalveolar lavage fluid after ovalbumin sensitization of guinea pigs.

Abstract

Arachidonic acid (AA), the precursor of eicosanoids, is released from the sn-2 position of phospholipids by both secretory (sPLA2) and cytosolic phospholipase A2 (cPLA2). Eicosanoids have been shown to contribute to bronchospasm in asthma. We measured the enzymatic activity of sPLA2 and cPLA2 in the bronchoalveolar lavage fluid and cells, respectively, in male Hartley guinea pigs sensitized with ovalbumin. sPLA2 activity was also measured from alveolar macrophages (AM) in culture from unsensitized and sensitized animals. There was an increase in sPLA2 activity and AA content in the lavage fluid following sensitization (18.73 +/- 1.33 to 25.74 +/- 3.22% hydrolysis and 17.97 +/- 12.39 to 44.76 +/- 13.37 pmol AA/mL BAL, mean +/- SD), which remained elevated but without further increase 4 or 24 h after antigen challenge. AM from unsensitized and sensitized-unchallenged animals did not secrete sPLA2 activity in culture for 3 h and therefore do not appear to be the cell source of the sPLA2 activity present in the alveolar lavage fluid following OA sensitization. In contrast to the increase in sPLA2 in lung lavage fluid, Western blotting for cPLA2 from lung lavage cells showed no increase 4 or 24 h after antigen challenge compared with sensitization alone. cPLA2 enzymatic activity of the cytosol fraction of lung lavage cells showed no changes with antigen sensitization or challenge. In summary, intraperitoneal sensitization with ovalbumin in male Hartley guinea pigs caused an increase in both sPLA2 and AA in bronchoalveolar lavage fluid without a need for antigen challenge. The increased sPLA2 enzymatic activity following sensitization may be responsible for the elevation of AA in the bronchoalveolar lavage fluid observed after antigen sensitization.