Activation of Human Granulocyte Type 1-Prophospholipase A₂

Abstract

Using an assay for measurement of released type 1-prophospholipase A₂ (type 1-proPLA₂) propeptides (PROP assay), we have shown that human granulocytes, but not lymphocytes or macrophages, abundantly express this ‘pancreatic’ type l-proPLA₂ zymogen. Stimulation with tumour necrosis factoralpha (TNF-α) and other cytokines results in the immediate release from granulocytes of a mixture of free propeptides and type 1-proPLA₂ precursor. We also found that granulocytes contain an approximately 29 kDa trypsin-like endogenous type 1-proPLA₂ activator. PROP assay and TAP (trypsinogen activation peptide) assay of plasma samples accurately predicts the segregation of acute pancreatitis into three clearly defined categories of severity—mild, intermediate and severe—at the time of first hospital admission and over the next few hours of observation. Mild and intermediate pancreatitis are associated with a degree of granulocyte stimulation limited to the release of the unactivated type 1-proPLA₂ precursor. Progression to severe disease is accompanied by the activation of granulocyte type 1-proPLA₂, apparently carried to completion. This identifies the approximately 29 kDa endogenous activator of type 1-proPLA₂ in granulocytes as a critical mediator at a threshold stage in acute pancreatitis, which marks the transition from uncomplicated pancreatitis to the potentially lethal disease. Specific inhibitors of this key regulatory enzyme modelled on the P3-P1 domain of the type 1-proPLA2 activation peptide would seem to be promising candidates for a new class of chemotherapeutic agents.

Key Words:

• Activation peptide assays
• acute pancreatitis
• PROP assay
• TAP assay
• type 1-prophospholipase A₂
• type 2-phospholipase A₂