Background: Inhalation of endotoxin may enhance inflammatory airway response in sensitized asthmatics persons after allergen(s) inhalation.

Objective: To evaluate nasal response to intranasal instillation of Dermatophagoides pteronyssinus (Dp), endotoxin (LPS), and to Dp+LPS in children with perennial allergic rhinitis (PAR).

Methods: 10 PAR children (positive skin prick test to Dp) and 10 nonallergic controls (C) undergoing nasal provocation test (NPT), who were quantified by active anterior rhinomanometry and measurement of Total Nasal Resistance (TNR). The NPTs were initially performed with histamine (H; 0.03 to 16.0 mg/mL), and then, at least at weekly intervals, the NPTs were done with Dp (1/100,000 to 1/2.5), LPS (1 to 500 mg/mL) and to Dp+LPS. During NPT with Dp+LPS, Dp concentration was kept constant (1/100,000; 1/10,000; 1/1,000) and was combined with different concentrations of LPS (1, 5, 10, 20 mg/mL). The NPT was considered positive when TNR reached twice the basal TNR.

Results: H and Dp NPTs were positive in all AR children. In group C, H NPT was positive in 60% and Dp NPT was negative in all children. NPT with LPS was positive only in 30% of the AR children. NPT with Dp+LPS was positive in 90% of the AR patients in Dp concentration of 1/1,000 and in LPS concentrations of 5, 10, and 20 mcg/ mL. This positive association was observed with Dp concentrations lower than those obtained during NPT with Dp in 60% of AR patients. There were no changes in pulmonary function tests in all children after NPT.

Conclusions: This study suggests that LPS enhances the effects of allergen challenges on nasal airflow. The daily
inhalation of allergens plus endotoxin in AR patients does increase the nasal responsiveness.

Key words: allergic rhinitis, mites, lipopolysaccharide, LPS, endotoxin, D. pteronyssinus