Immunology of the Upper Airway and Pathophysiology and Treatment of Allergic Rhinitis

• The immune system protects the organism from infectious microbes and avoids responses that produce damage to host tissues. • The immune system is divided into the innate and adaptive systems. The adaptive immune system recognizes different specific antigens, adapts to changing environments, and provides immunologic memory. • The innate immune system includes all aspects of the host defense mechanisms, such as barrier mechanisms (epithelium, mucus layer, mucociliary transport) and soluble bioactive molecules (complement proteins, defensins, cytokines, mediators, and enzymes). • Cell-mediated immune responses are orchestrated by T cells and their cytokines and mount appropriate reactions to offending antigens. • Allergic rhinitis is an example of a type I, IgE-dependent, mast cell–mediated immune reaction, whereby the release of mast cell or basophil mediators creates responses to sensitizing allergens. • Allergic rhinitis is a common disease that, although benign, leads to significant impairment of quality of life and a large health care expenditure. • The pathophysiology of allergic rhinitis revolves around mast cell release of inflammatory mediators followed by a chronic inflammatory response, in which the eosinophil plays a predominant role and which leads to hyperresponsiveness of the nasal mucosa to subsequent stimulation. • H1 antihistamines are effective agents for the treatment of allergic rhinitis but often do not completely control the bothersome symptom of nasal congestion. • Leukotriene receptor antagonists are also effective in controlling the symptoms of allergic rhinitis, and their efficacy parallels that of antihistamines. • Intranasal steroids are potent anti-inflammatory agents that control allergic nasal inflammation and are superior in efficacy to antihistamines and leukotriene receptor antagonists in controlling symptoms of the disease and improving quality of life. • Immunotherapy is effective in the treatment of refractory allergic rhinitis and can be administered subcutaneously or by the sublingual route. • Immunotherapy is the only allergic rhinitis therapy that has been shown to alter the natural course of the disease.