Pathogenic mechanisms underlying the clinical symptoms of allergic rhinitis

This paper reviews our previous studies on an objective evaluation of nasal symptoms, a quantitative determination of biochemical mediators, and inflammatory cells in nasal secretions of atopic patients after nasal allergen challenge (NAC) and during natural allergen exposure. The use of the microsuction technique has proved to be a useful and reliable nasal sampling method permitting quantitative analysis of important mediators in nasal secretions. This has provided accurate data on the activity of some important inflammatory cells such as mast cells, basophils, and eosinophils in allergic rhinitis. Our studies demonstrate that a significant increase in the concentrations of histamine, tryptase, and LTC4 in nasal secretions occurs within seconds or minutes after NAC, and this is accompanied by itching, sneezing, rhinorrhea, and nasal obstruction. The infiltration and activation of eosinophils are found to be the predominant condition during the late-phase reaction (LPR), which is mainly characterized by unilateral and/or bilateral nasal obstruction with little sneezing and rhinorrhea. The latter condition is found to be very much similar to the pathophysiology of patients with ongoing allergic rhinitis. In conclusion, our studies demonstrate that patients with ongoing allergic rhinitis seem to be in a continuous late phase state of eosinophilia and increased mediator release, a condition that can explain priming and nonspecific hyperreactivity of the nasal mucous membrane.