Involvement of eosinophils in the early-phase allergic reaction in a guinea pig rhinitis model

Eosinophils are found in the nasal lavage fluid (NLF) and nasal biopsies of patients with allergic rhinitis after a nasal antigen challenge, and associated not only with a late-phase allergic reaction (LPR) but also an early phase allergic reaction (EPR). Numerous studies have been carried out to clarify the participation of eosinophils in LPR or airway hyperresponsiveness. However, there has been no published report describing in detail the role of eosinophils during EPR. To better understand the involvement of eosinophils in EPR, we studied the effects of repeated antigen challenges on nasal airway responsiveness and eosinophilic inflammation in EPR using a guinea pig rhinitis model.

Nasal airway responsiveness was measured as the nasal airway resistance (NAR) after nasal antigen provocation. Eosinophilic inflammation during EPR was assessed by nasal lavage and histopathological examination using two groups of animals: those in group 1 were subjected to a sensitization pretreatment only, and those in group 2 were subjected to a pretreatment of sensitization followed by repeated nasal challenges.

Repeated antigen challenges induced nasal hyperresponsiveness as indicated by a decrease in the antigen provocation dose and a significant increase in NAR. Furthermore, significant increases in eosinophil counts, eosinophil peroxidase (EPO) activity and protein content in NLF during EPR were observed following antigen provocation in group 2. There were significant correlations between the levels of these parameters, and albumin was the most prevalent of the proteins in NLF. Histopathological examination showed that the degree of eosinophil infiltration into the lamina propria of the nasal mucosa of the animals in group 2 was significantly and apparently higher than in group 1. Particularly, epithelial disruption and mucosal edema were significantly elevated after antigen provocation in group 2.

These results suggest that chronic eosinophil accumulation is induced by repeated antigen challenges in the nasal tissue, and that once antigen provocation occurs, eosinophils in the tissue are activated and responsible for the amplification of EPR such as vascular permeability and mucosal edema.