INCREASED PLASMA PLATELET-ACTIVATING-FACTOR IN CHILDREN WITH ACUTE ASTHMATIC ATTACKS AND DECREASED INVIVO AND INVITRO PRODUCTION OF PLATELET-ACTIVATING-FACTOR AFTER IMMUNOTHERAPY

Background: To explore the possible role of platelet-activating factor (PAF) in the pathogenesis of bronchial asthma, circulating PAF and in vitro production of PAF were studied. Methods: Radioimmunoassay kits were used in 15 children with acute asthmatic attacks, in 25 newly diagnosed asthmatic children, in 25 good and 18 poor responders to immunotherapy, and in 18 healthy controls. Results: The results demonstrated the following: (1) PAF was present in the blood of healthy controls. (2) New patients had much higher circulating PAF than did healthy controls (p < 0.005), and the circulating PAF decreased after immunotherapy in good (p < 0.005) but not in poor responders. (3) The circulating PAF increased up to 20 times that of healthy controls during acute asthmatic attacks. (4) The spontaneous and allergen-stimulated secretion of PAF were markedly increased in new patients and decreased to normal after successful immunotherapy (p < 0.005). (5) No increased spontaneous and allergen-stimulated production of PAF was found during acute attacks, but granulocytes from those patients still produced the greatest amount of PAF when stimulated with calcium ionophore A23187. (6) Although a major portion of allergen-induced PAF was secreted, less than 10% of ionophore-induced PAF was secreted. Conclusion: The findings that the circulating PAF increased markedly during acute asthmatic attacks and the enhanced in vivo and in vitro productions of PAF decreased to normal after successful immunotherapy strongly suggest that PAF may be involved in the pathogenesis of bronchial asthma.