Blocking the leukotriene B4 receptor 1 inhibits late-phase airway responses in established disease

Abstract

Most of the studies investigating the effectiveness of blocking the leukotriene B4 (LTB4) receptor 1 (BLT1) have been performed in models of primary or acute allergen challenge. The role of the LTB4-BLT1 pathway in secondary challenge models, where airway hyperresponsiveness (AHR) and airway inflammation have been established, has not been defined. We investigated the effects of blocking BLT1 on early- and late-phase development of AHR and airway inflammation in previously sensitized and challenged mice. Female BALB/c mice were sensitized (Days 1 and 14) and challenged (primary, Days 28-30) with ovalbumin. On Day 72, mice were challenged (secondary) with a single OVA aerosol, and the early and late phases of AHR and inflammation were determined. Specific blockade of BLT1 was attained by oral administration of a BLT1 antagonist on Days 70 through 72. Administration of the antagonist inhibited the secondary ovalbumin challenge-induced alterations in airway responses during the late phase but not during the early phase, as demonstrated by decreases in AHR and in bronchoalveolar lavage neutrophilia and eosinophilia 6 and 48 hours after secondary challenge. The latter was associated with decreased levels of KC protein, macrophage inflammatory protein 2, and IL-17 in the airways. These data identify the importance of the LTB4-BLT1 pathway in the development of late-phase, allergen-induced airway responsiveness after secondary airway challenge in mice with established airway disease.

Figure 1.

Altered airway function in the early asthmatic response. All groups were exposed to secondary challenge with 5% ovalbumin (OVA), and changes in lung resistance (R_L) were monitored. Administration of the BLT1 antagonist was as described in Materials and Methods. n = 12 in each group. Means ± SEM are shown. *P < 0.05. PBS/OVA/vehicle PBS/OVA/antagonist versus OVA/OVA/vehicle OVA/OVA/antagonist. PBS/OVA = nonsensitized and challenged. OVA/Saline = sensitized and challenged and secondary challenged with saline. OVA/OVA = sensitized and challenged.

Figure 2.

Altered airway function during the late asthmatic response. Previously sensitized and challenged mice were exposed to secondary allergen challenge, and changes in R_L were monitored 6 hours later. n = 12 in each group. Means ± SEM are shown. *P < 0.05 compared with OVA/OVA/vehicle group.

Figure 3.

BLT1 antagonist reduces AHR and airway inflammation 6 hours after secondary challenge. (A) R_L was measured in sensitized and challenged mice 6 hours after the secondary provocation with OVA. n = 12 in each group. *P < 0.05 compared with all other groups. (B) Cellular composition in bronchoalveolar lavage (BAL) fluid. (C) BAL cytokine levels. (D) BAL chemokine levels. (E) BAL IL-17 levels. *P < 0.05 compared with OVA/OVA/vehicle.

Figure 4.

(A) Effect of BLT1 antagonist treatment on tissue inflammation and goblet cell metaplasia in sensitized and challenged mice 6 hours after secondary allergen challenge. (B) Eosinophil quantitation. *P < 0.05 compared with OVA/OVA/vehicle. (C) PAS-stained sections 6 hours after secondary allergen challenge.

Figure 5.

BLT1 antagonist reduces AHR and airway inflammation 48 hours after secondary challenge. (A) R_L was measured in sensitized and challenged mice 48 hours after secondary OVA provocation. *P < 0.05 compared with all other groups. (B) Cellular composition in BAL fluid. (C) BAL cytokine levels. (D) BAL chemokine levels. (E) H&E staining. (F) Lung cell composition. (G) Periodic acid-Schiff staining. *P < 0.05 compared with OVA/OVA/vehicle. n = 12 in each group. *P < 0.05 compared with OVA/OVA/vehicle.