Characterization of a secretory phospholipase A(2) in human bronchoalveolar lavage fluid

Phospholipase A(2) (PLA(2)) is a pivotal enzyme involved in the synthesis of the potent lipid inflammatory mediators platelet activating factor (PAF) and the eicosanoids. This study characterizes a PLA(2) recovered in the bronchoalveolar lavage fluid (BALF) of healthy adult human subjects. Human BALF PLA(2) exhibited characteristics of secretory PLA(2)s that include an activity that is acid stable, sensitive to reducing agents, and optimally requires millimolar calcium. BALF PLA(2) showed marked selectivity for phosphatidylcholine containing arachidonic acid (AA) over linoleic or palmitic acids. Size exclusion chromatography showed the BALF PLA(2) protein to be approximately 14 kDa in mass, consistent with it being a secretory form of PLA(2). The biological significance of BALF PLA(2) was tested by applying BALF concentrates to cultures of the human bronchial epithelial cell line BEAS 2B. Cultures of BEAS 2B cells treated with BALF concentrates released amounts of AA and produced higher levels of PAF. These data show that the lining fluid of the human respiratory tract normally contains a secretory PLA(2), which may be involved in the formation of lipid inflammatory mediators in normal and pathophysiologic states in the lung.