UC Davis

Background

Ozone (O₃) inhalation elicits airway inflammation and impairs treatment responsiveness in asthmatic patients. The underlying immune mechanisms have been difficult to study because of the lack of relevant experimental models. Rhesus macaques spontaneously have asthma and have a similar immune system to human subjects.

Objectives

We sought to investigate mucosal immune changes after O₃ inhalation in a clinically relevant nonhuman primate asthma model and to study the effects of an antioxidant synthetic lignan (synthetic secoisolariciresinol diglucoside [LGM2605]).

Methods

A cohort of macaques (n = 17) previously characterized with airway hyperreactivity (AHR) to methacholine was assessed (day 1). Macaques were treated (orally) with LGM2605 (25 mg/kg) or placebo twice per day for 7 days, exposed to 0.3 ppm O₃ or air for 6 hours (on day 7), and studied 12 hours later (day 8). Lung function, blood and bronchoalveolar lavage (BAL) fluid immune cell profile, and bronchial brushing and blood cell mRNA expression were assessed.

Results

O₃ induced significant BAL fluid neutrophilia and eosinophilia and increased AHR and expression of IL6 and IL25 mRNA in the airway epithelium together with increased BAL fluid group 2 innate lymphoid cell (ILC2s), CD1c⁺ myeloid dendritic cell, and CD4⁺ T-cell counts and diminished surfactant protein D expression. Although LGM2605 attenuated some of the immune and inflammatory changes, it completely abolished O₃-induced AHR.

Conclusion

ILC2s, CD1c⁺ myeloid dendritic cells, and CD4⁺ T cells are selectively involved in O₃-induced asthma exacerbation. The inflammatory changes were partially prevented by antioxidant pretreatment with LGM2605, which had an unexpectedly disproportionate protective effect on AHR.