Bronchial hyper-responsiveness (BHR) is documented in a proportion of non-asthmatic individuals with
allergic rhinitis (NAAR) and reflects inflammatory events in the lower airways. Natural exposure to
allergens is known to modulate BHR and the level of airway
inflammation in
asthma, but less consistently in NAAR. Specific
immunotherapy (SIT) attenuates symptoms possibly by reducing BHR and airway
inflammation. The influence of natural exposure to Parietaria pollen on BHR and sputum cell counts of NAAR was investigated and the effect of Parietaria SIT examined. Thirty NAAR, monosensitized to Parietaria judaica, participated in a randomized, double-blind, placebo-controlled, parallel group study of the effects of a Parietaria pollen
vaccine on symptoms/medication score, BHR to inhaled
methacholine and
adenosine 5'-monophosphate (
AMP), and cell counts in the sputum collected out of and during the pollen seasons for 36 months. Seasonal variation in BHR to inhaled
methacholine and
AMP and changes in sputum cell counts were documented. Changes were consistent for
AMP, but not
methacholine, and invariably associated with modifications in sputum eosinophils and epithelial cells. The clinical efficacy of Parietaria SIT was associated with a decline in the seasonal deterioration of BHR to
AMP, whereas no significant effect was observed on BHR to
methacholine or sputum cell differentials. Between-groups comparison of the seasonal changes in PC15
methacholine values and sputum cell differentials calculated as the AUC were not statistically significant, whereas a significant difference in PC15
AMP was demonstrated throughout the study (P=0.029), the median (inter-quartile range) AUC values being 2478.5 (1153.3-3600.0) and 1545.5 (755.3-1797.9) for the SIT- and placebo-treated group, respectively. Bronchial airways of NAAR exhibit features of active
inflammation that deteriorate during natural
allergen exposure, particularly with regard to BHR to
AMP. The clinical efficacy of Parietaria SIT was exclusively associated with attenuation in seasonal worsening of PC15
AMP, suggesting that
AMP may be useful in monitoring changes in allergic
inflammation of the airways.