What chemical mediator is responsible for respiratory distress (ex coughing/asthma)?

histamine

The chemically-rich mast cells that line the bronchial mucous membranes may release histamine or other chemical mediators, which can cause bronchospasm and bronchial inflammation. In allergic asthma, the allergy antibody, IgE, can cause the mast cells to release chemicals when exposed to appropriate allergen(s).

source: The Asthma Center Education and Research

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