Presence of the M-type sPLA2 receptor on neutrophils and its role in elastase release and adhesion

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Abstract
Secretory phospholipase A2 (sPLA2) produces lipids that stimulate polymorphonuclear neutrophils (PMNs). With the discovery of sPLA2 receptors (sPLA2-R), we hypothesize that sPLA2 stimulates PMNs through a receptor. Scatchard analysis was used to determine the presence of a sPLA2ligand. Lysates were probed with an antibody to the M-type sPLA2-R, and the immunoreactivity was localized. PMNs were treated with active and inactive (+EGTA) sPLA2 (1–100 units of enzyme activity/ml, types IA, IB, and IIA), and elastase release and PMN adhesion were measured. PMNs incubated with inactive, FITC-linked sPLA2-IB, but not sPLA2-IA, demonstrated the presence of a sPLA2-R with saturation at 2.77 fM and a K d of 167 pM. sPLA2-R immunoreactivity was present at 185 kDa and localized to the membrane. Inactive sPLA2-IB activated p38 MAPK, and p38 MAPK inhibition attenuated elastase release. Active sPLA2-IA caused elastase release, but inactive type IA did not. sPLA2-IB stimulated elastase release independent of activity; inactive sPLA2-IIA partially stimulated PMNs. sPLA2-IB and sPLA2-IIA caused PMN adhesion. We conclude that PMNs contain a membrane M-type sPLA2-R that activates p38 MAPK.