Induction of the activation-related antigen CD69 on human eosinophils by type IIA phospholipase A2

High levels of human type IIA phospholipase A2 (PLA2-IIA) have been found in the eosinophil-mediated inflammation sites, although the pathophysiological role of PLA2-IIA in the eosinophil activation has remained poorly understood. We investigated the effects of PLA2-IIA on eosinophil activation.

Eosinophils were incubated with recombinant human PLA2-IIA or other stimuli, and then eosinophil peroxidase (EPO) (by colorimetric assay) and leukotriene C4 (by enzyme immunoassay) released in the incubation buffer were measured. Expression of CD11b and CD69 on the cell surface was also measured by flow cytometry (by mean fluorescence intensity (MFI)). EPO, LTC4, and CD11b are thought to be markers for early phase activation (occurred in an hour after stimulation), and CD69 is to be a marker for late phase activation (occurred after several hours).

While PLA2-IIA (5 microg/ml) did not induce any early phase activation, it induced significant expression of an activation-related antigen, CD69, on human blood eosinophils. The PLA2-IIA, when enzymatically inactivated by either p-bromophenacyl bromide or EDTA, lost its effect on the CD69 induction. Similarly to PLA2-IIA, several lysophospholipids (1 microg/ml) also induced CD69 on eosinophils significantly (control, 0.71 +/- 0.11; PLA2-IIA, 3.29 +/- 0.37*; lysophosphatidic acid, 2.57 +/- 0.43*; specific MFI +/- S.E.M., n = 4, * indicate p < 0.05 vs. control).

PLA2-IIA induces CD69 expression on the eosinophils through its catalytic activity at least partly via the enzymatic products such as several lysophospholipids from the eosinophil membrane phospholipids. PLA2-IIA may contribute to the eosinophilic inflammation synergistically with other factors.