The influence of sensitization on mechanisms of organophosphorus pesticide-induced airway hyperreactivity

Abstract

We previously demonstrated that antigen sensitization increases vulnerability to airway hyperreactivity induced by the organophosphorus pesticide (OP) parathion. Sensitization also changes the mechanism of parathion-induced airway hyperreactivity to one that is dependent on IL-5. To determine whether this effect can be generalized to other OPs, and to other classes of pesticides, we measured airway responsiveness to vagal stimulation or intravenous acetylcholine in nonsensitized and ovalbumin-sensitized guinea pigs 24 hours after a single subcutaneous injection of the OPs diazinon or chlorpyrifos, or the pyrethroid permethrin. Sensitization exacerbated the effects of chlorpyrifos on bronchoconstriction in response to vagal stimulation or intravenous acetylcholine. Pretreatment with function-blocking IL-5 antibody prevented chlorpyrifos-induced airway hyperreactivity in sensitized, but not in nonsensitized, guinea pigs. In sensitized guinea pigs, blocking IL-5 decreased eosinophil activation, as measured by decreased eosinophil major basic protein in the trachea. In contrast, sensitization did not alter diazinon-induced airway hyperreactivity, and permethrin did not cause airway hyperreactivity in either nonsensitized or sensitized guinea pigs. None of the pesticides affected inflammatory cells in the bronchoalveolar lavage fluid or blood. We have previously shown that three different OPs cause airway hyperreactivity via loss of neuronal M2 muscarinic receptor function. Similar to parathion, but unlike diazinon, the mechanism of chlorpyrifos-induced airway hyperreactivity is changed by sensitization. Thus, OP-induced airway hyperreactivity is dependent on sensitization status and on the OP used, which may influence therapeutic approaches.

Keywords: airway hyperreactivity; eosinophils; organophosphorus pesticides; permethrin; sensitization.

Figure 1.

Airway physiology and acetylcholinesterase (AChE) activity in nonsensitized and sensitized guinea pigs treated with the organophosphorus pesticide (OP) chlorpyrifos (CPF) in the presence or absence of antibody to IL-5 (AbIL5). Vagally induced (A, B, E, and F) and acetylcholine (ACh)-induced (C, D, G, and H) bronchoconstrictions were measured in nonsensitized (A, C, E, and G) and sensitized (B, D, F, and H) animals 24 hours after subcutaneous injection of 0.7–70 mg/kg CPF. A subset of animals was injected intraperitoneally with AbIL5 3 days before exposure to CPF at 70 mg/kg subcutaneous (E–H). Data from animals injected with CPF at 70 mg/kg shown in E–H are the same data shown in A–D. AChE activity was measured in blood (I) and brain (J) collected from guinea pigs immediately after physiological studies were concluded. Data are presented as mean ± SEM. *P < 0.05 compared with respective controls, ^#P < 0.05 compared with equivalent treatment in nonsensitized animals, ⁺P < 0.05 compared with sensitized/70 m/kg CPF. i.v., intravenous; Ppi, pulmonary inflation pressure.

Figure 2.

Airway physiology and AChE activity measurements in nonsensitized and sensitized guinea pigs treated with the OP diazinon (DZN). Vagally induced (A–C) and ACh-induced (D–F) bronchoconstrictions were measured in nonsensitized (A and D) and sensitized (B, C, E, and F) animals 24 hours after subcutaneous injection of DZN. Additional sensitized animals were injected intraperitoneally with AbIL5 3 days before DZN was administered subcutaneously at 75 mg/kg (C and F). AChE activity was measured in blood (G) and brain (H). Data are presented as mean ± SEM. *P < 0.05 compared with respective controls.

Figure 3.

Airway physiology and AChE activity measurements in nonsensitized and sensitized guinea pigs treated with the pyrethroid permethrin (PERM). Vagally induced (A and B) and ACh-induced (C and D) bronchoconstrictions were measured in nonsensitized (A and C) and sensitized (B and D) animals 24 hours after subcutaneous injection of PERM. AChE activity was measured in blood (E) and brain (F). Data are presented as mean ± SEM. *P < 0.05.

Figure 4.

Quantification of the number of eosinophils and major basic protein (MBP) deposition in the lungs of sensitized guinea pigs exposed to 70 mg/kg CPF with or without pretreatment with AbIL5. All images are representative of those used for data collection. (A) The number of eosinophils (red) within 8 μm (*) of an airway nerve (protein gene product [PGP] 9.5, dark gray, indicated by arrowheads) were counted and normalized to the area of airway measured, which included the submucosal region under the basal lamina through to the connective tissue adjoining the alveoli, which includes airway smooth muscle. (B) The intensity of MBP immunoreactivity (red) was measured in airway nerve bundles labeled with PGP 9.5 (green). MBP intensity was normalized to area of nerve bundle. (C) The area of MBP staining was quantified in whole lung sections and normalized to total lung area analyzed (excluding luminal space). (D) The area of MBP immunoreactivity was quantified in epithelium and underlying connective tissue in the trachea and then normalized to the total area analyzed. (E) The number of eosinophils (red) located between the basement membrane and either the cartilage or alveoli were quantified and normalized to the total area analyzed. (F) The area of MBP immunoreactivity was quantified as in E. Data are presented as mean ± SEM. *P < 0.05.