Platelets Play a Central Role in Sensitization to Allergen.
Platelet activation occurs in patients with allergic inflammation, and platelets can be activated directly by allergen via an IgE-dependent process. Platelets activate antigen-presenting cells (APCs) such as CD11c+ dendritic cells (DCs) in vitro. Whilst CD11c+ DCs are requisite for allergen sensitization, the role of platelets in this process is unknown.OBJECTIVES
We investigated whether platelets were necessary for allergen sensitization.METHODS
Balb/c mice sensitised to ovalbumin (OVA), were exposed to subsequent aerosolized allergen (OVA challenge). We analysed lung CD11c+ cell activation, co-localization with platelets, and some other indices of inflammation. The role of platelets at the time of allergen sensitization was assessed through platelet depletion experiments restricted to the period of sensitization.RESULTS
Platelets co-localized with airway CD11c+ cells, and this association increased after allergen sensitization, and after subsequent allergen exposure. Temporary platelet depletion (>95%) at the time of allergen sensitization led to a suppression of IgE and IL-4 synthesis, and a decrease in the pulmonary recruitment of eosinophils, macrophages, and lymphocytes after subsequent allergen exposure. Furthermore, in mice previously depleted of platelets at the time of sensitization, the recovered platelet population were shown to have reduced expression of FcɛRI. Pulmonary CD11c+ cell recruitment was suppressed in these mice after allergen challenge, suggesting the migration of CD11c+ cells in vivo may be dependent on direct platelet recognition of allergen.CONCLUSION
Platelets are necessary for efficient host sensitization to allergen. This propagates the subsequent inflammatory response during secondary allergen exposure, and increases platelet association with airway CD11c+ cells.