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Platelet dynamics following allergen challenge in allergic asthmatics
P J Sullivan1, Z H Jafar, P L Harbinson
1Sackler Institute of Pulmonary Pharmacology, Division of Pharmacology and Therapeutics, GKT School of Biomedical Sciences, and Division of Respiratory Medicine, King's College, London, UK.
Background:
There is evidence that platelet activation occurs in allergic inflammation and asthma, but little is known about the role platelets play in airway inflammation associated with asthma.
Objectives:
In the present study, we have investigated the kinetics of platelet activation following allergen provocation of allergic asthmatics to determine the dynamics of platelet activation relative to changes in lung function and changes in airway inflammation.
Methods:
Changes in platelet count and haematocrit from baseline were measured during the early asthmatic response (EAR), late asthmatic response (LAR; or at corresponding time points) and at 24 h were compared between allergen- and saline-challenged groups. A subgroup of allergen-challenged asthmatics, a group of 7 challenged asthmatics and 7 controls were bronchoscoped, and BAL fluid was collected and analysed for levels of histamine and eosinophil cationic protein.
Results:
There was a fall in circulating platelet count, but not haematocrit after allergen challenge when compared with saline during the LAR or at 24 h. At 24 h FEV(1) had returned to within 20% of baseline in all subjects, although the thrombocytopaenia and airway inflammation persisted.
Conclusions:
Our results suggest that persistent thrombocytopaenia accompanies allergen exposure and persists beyond changes in airway obstruction at a time when airway inflammation is present. Our results provide further evidence that platelets may be involved in allergic disease.