Assessment of a role for phospholipase A2 and arachidonic acid metabolism in human lymphocyte natural cytotoxicity.

The reagents quinacrine, hydrocortisone, and dexamethasone have been assumed to affect phospholipase A2 (PA2) when they reduce natural killer (NK) activity. However, these reagents did not reduce lymphocyte incorporation of [14C]arachidonate, which implies that they are not acting as PA2 inhibitors in this lymphocyte system. However, p-bromophenacyl bromide (BPB), which is an active site inhibitor of PA2, irreversibly abrogated NK activity of pretreated lymphocytes, disrupted target cell binding, and reduced [14C]arachidonic acid incorporation by 70-80% as compared to controls. Other observations contrary to expectations for PA2 inhibitors were: (1) quinacrine inhibited NK lysis when lymphocytes were pretreated and (2) the glucocorticoids only inhibited NK activity when continuously present in the assay. Furthermore, NK inhibition by hydrocortisone did not require protein synthesis. The lipoxygenase inhibitors, nordihydroguaiaretic acid (NDGA), 5,8,11,14-eicosotetraynoic acid (ETYA), and hydroxyphenylretinamide, and not cycloxygenase inhibitors, reduced NK activity. These data suggest that arachidonate must be metabolized through the 5-lipoxygenase pathway in order to function in NK.