The evidence of platelet activation in bronchial asthma.

The possible involvement of platelets in bronchial asthma was investigated under three different conditions: (1) chronic asthma, (2) bronchial provocation inhaling house dust mite (HDM), and (3) status asthmaticus. Plasma levels of beta-thromboglobulin (beta-TG), platelet factor 4 (PF4), and in part, platelet-activating factor (PAF) were measured. Approximately one third of the subjects with symptomatic or asymptomatic chronic asthma showed an increased level of beta-TG or PF4. Statistically significant differences occurred in beta-TG and PF4 levels only between healthy controls and symptomatic subjects. Five out of six subjects showed no elevation of beta-TG and PF4 during immediate asthmatic response. In two out of nine subjects with status asthmaticus, beta-TG or PF4 was elevated, and statistically significant correlations occurred between the initial level of PAF and that of beta-TG or PF4. Those results suggest that the platelet activation in the circulation is sometimes provoked in asthma, but plasma level of alpha-granule-derived proteins does not reflect the intensity or severity of asthma, and that PAF is likely to be a mediator responsible for the platelet activation.