Inhalation of the reactive aldehyde acrolein promotes antigen sensitization to ovalbumin and enhances neutrophilic inflammation

Abstract

Acrolein (ACR), an α,β-unsaturated aldehyde and a major component of tobacco smoke, is a highly reactive electrophilic respiratory irritant implicated in asthma pathogenesis and severity. However, few studies have directly investigated the influence of ACR exposure on allergen sensitization and pulmonary inflammation. The present study was designed to examine the impact of ACR inhalation on allergic sensitization to the inhaled antigen ovalbumin (OVA), as well as pulmonary inflammation during subsequent OVA challenge. Adult male C57BL/6 mice were exposed to inhaled OVA (1%, 30 min/day, 4 days/week) and/or ACR (5 ppm, 4 h/day, 4 days/week) over 2 weeks and subsequently challenged with aerosolized OVA (1%, 30 min/day) over three consecutive days. Serum anti-OVA IgG1 levels were increased significantly in animals exposed to both OVA and ACR, compared to animals exposed to either OVA or ACR alone. In addition, differential cell counts and histological analysis revealed an increase in BAL neutrophils in animals exposed to both OVA and ACR. However, exposure to both OVA and ACR did not influence mRNA expression of the cytokines il5, il10, il13 or tnfa, but significantly increased mRNA expression of ccl20. Moreover, ACR exposure enhanced lung mRNA levels of il17f and tgfb1, suggesting development of enhanced inhalation tolerance to OVA. Overall, the findings indicate that ACR inhalation can promote airway-mediated sensitization to otherwise innocuous inhaled antigens, such as OVA, but also enhances immune tolerance, thereby favoring neutrophilic airway inflammation.

Keywords: Acrolein; allergic asthma; inflammation; ovalbumin.

Figure 1

Schematic diagram of ACR and OVA administrations. On indicated days, mice were exposed to 5 ppm ACR for 4 h (squares) and/or 1% OVA in PBS for 30 min (circles). All animals treated with ACR only, OVA only, or OVA and ACR were challenged with OVA on days 19–21. Sample collection occurred on Day 23. Naive mice received no treatment.

Figure 2

Anti-OVA IgG₁ levels in sera from naive, ACR-, OVA-, and OVA/ACR-treated animals collected on Day 23. Bars represent mean ± SEM. *p < 0.05 and **p < 0.005 compared between indicated treatment groups. OD: Optical Density. Naive: n = 4; ACR, OVA, and OVA/ACR: n =10–14

Figure 3

(A) Airway influx of total leukocytes and (B) airway influx of macrophages, neutrophils, lymphocytes, and eosinophils in BALF of naive, ACR-, OVA-, and OVA/ACR-treated animals collected on Day 23. Bars represent mean ± SEM. *p < 0.05 and **p < 0.01 compared between indicated treatment groups. Naive: n = 4; ACR, OVA, and OVA/ACR: n = 14. (C) Representative lung sections from OVA-, ACR-, and OVA/ACR-treated mice collected after subsequence OVA challenge and stained with H&E. Bar = 50 µm.

Figure 4

mRNA expression of ccl20, il1a, il17f, and tfgb1 in lung tissue of naive, ACR-, OVA-, and OVA/ACR-treated animals collected on Day 23. Bars represent mean ± SEM. *p < 0.05, **p < 0.01, and ***p < 0.001 compared to control (open bar) or between treatment groups indicated by line. RQ: relative quantifications. Naive: n = 2–5; ACR, OVA, and OVA/ACR: n = 8–11.