Allergy, Histamine and Antihistamines

This chapter concentrates on the role in allergic disease of histamine acting on H₁-receptors. It is clear that allergy has its roots in the primary parasite rejection response in which mast cell-derived histamine creates an immediate hostile environment and eosinophils are recruited for killing. This pattern is seen in allergic rhinitis where the early events of mucus production and nasal itching are primarily histamine mediated whereas nasal blockage is secondary to eosinophil infiltration and activation. In asthma, the role of histamine is less clear. Urticaria is characterized by mast cell driven pruritic wheal and flare-type skin reactions that usually persist for less than 24 h. Although the events leading to mast cell degranulation have been unclear for many years, it is now becoming evident that urticaria has an autoimmune basis. Finally, the properties of first- and second-generation H₁-antihistamines and their role in allergic is discussed.