The effects of antihistamines beyond H1 antagonism in allergic inflammation.

Antigen and cold dry air were used to challenge the upper and lower airways, skin, and conjunctiva. In each of these four systems an immediate and late-phase reaction to antigen is well characterized. Although the pattern of mediator release is different in these four areas, the degree of infiltration of basophils and eosinophils in the late-phase reaction appears to be constant. Of a number of drugs that can influence these mediators and cell responses, the steroids represent a typical mode of action. Steroids block the late-phase response and ablate the eosinophil and basophil infiltration. Although the effects of antihistamines appear to be similar, they do not appear to be caused by H1 antagonism; the mechanism of their action is unknown. This discussion will focus on these non-H1 antagonist effects of antihistamines in four challenge models, particularly the upper airways and skin.