Platelet reactivity to "in vitro" allergen challenge in asthmatic patients

Platelet involvement in inflammation and allergic states is now well documented. In fact, it has been suggested that platelets can be triggered by either activated cells as monocytes and macrophages or by allergen itself. This latter possibility is still a matter of controversy. In this study we analysed platelet "in vitro" response to allergen, by optical aggregation technique, in 25 asthmatic patients, being 20 atopic and 5 non atopic patients. Platelet aggregation response to epinephrine, ADP, collagen and arachidonic acid was studied in all patients. In addition, allergen was added to platelet rich plasma and platelet reactivity was recorded both before and after stimulations with collagen. Platelet aggregation studies confirmed and abnormality of ADP induced platelet aggregation, that exhibited great variability among patients. In most cases this defect was the only one found in asthmatic patients and it should be further analysed. Results also showed a nonspecific response to allergen when dissolved in glycerol. This was due to glycerol rather than to allergen, since lyophilized allergen did not affect platelets, and glycerol added to platelet rich plasma induced the same type of curve. So, allergen by itself does not imply platelet aggregation. Experiments with IgE did not provoke either platelet agglutination or platelet aggregation. Furthermore, previous incubation with allergen immediately before collagen induced aggregation did not significantly change platelet response. This study allows the conclusion that platelet reactivity to allergen contact must be an expression of multicellular cooperation rather than a direct effect on platelet IgE receptors stimulation.