Sympathetic Nerves Positively Regulate Eosinophil-Driven Allergic Conjunctivitis via α1-Adrenergic Receptor Signaling.

Eosinophils are a major cause of tissue injury in allergic conjunctivitis. The biological nature of eosinophils in the conjunctiva and the mechanisms that control eosinophils' responses in allergic conjunctivitis are currently not completely understood. Here, we report that conjunctival eosinophils comprise two populations-Siglec horizontal line F(int) and Siglec horizontal line F(hi)-in different life stages. Siglec horizontal line F(int) eosinophils partly expressed CD34 and were in the immature (or steady) state. Siglec horizontal line F(hi) eosinophils did not express CD34, sharply increased in number after short ragweed (SRW) pollen challenge, and were in the mature (or activated) state. Moreover, chemical sympathectomy by 6 horizontal line hydroxydopamine reduced the recruitment and activation of eosinophils, while the activation of sympathetic nerve system (SNS) with restraint stress accelerated the recruitment and activation of eosinophils in SRW horizontal line induced conjunctivitis. We also found that two eosinophil populations expressed alpha horizontal line 1a horizontal line adrenergic receptors (alpha1a horizontal line ARs); in SRW horizontal line induced conjunctivitis, treatment with an alpha1a horizontal line AR antagonist decreased eosinophil responses, whereas treatment with an alpha1a horizontal line AR agonist aggravated eosinophil responses. Thus, eosinophil responses in conjunctivitis are regulated by the SNS via alpha1a horizontal line AR signaling. SNS inputs or alpha1a horizontal line AR function may be potential targets for the treatment of allergic conjunctivitis.