Pulmonary exposure to particles during pregnancy causes increased neonatal asthma susceptibility

Abstract

Maternal immune responses can promote allergy development in offspring, as shown in a model of increased susceptibility to asthma in babies of ovalbumin (OVA)-sensitized and -challenged mother mice. We investigated whether inflammatory responses to air pollution particles (diesel exhaust particles, DEP) or control "inert" titanium dioxide (TiO(2)) particles are enhanced during pregnancy and whether exposure to particles can cause increased neonatal susceptibility to asthma. Pregnant BALB/c mice (or nonpregnant controls) received particle suspensions intranasally at Day 14 of pregnancy. Lung inflammatory responses were evaluated 48 hours after exposure. Offspring of particle- or buffer-treated mothers were sensitized and aerosolized with OVA, followed by assays of airway hyperresponsiveness (AHR) and allergic inflammation (AI). Nonpregnant females had the expected minimal response to "inert" TiO(2). In contrast, pregnant mice showed robust and persistent acute inflammation after both TiO(2) and DEP. Genomic profiling identified genes differentially expressed in pregnant lungs exposed to TiO(2). Neonates of mothers exposed to TiO(2) (and DEP, but not PBS) developed AHR and AI, indicating that pregnancy exposure to both "inert" TiO(2) and DEP caused increased asthma susceptibility in offspring. We conclude that (1) pregnancy enhances lung inflammatory responses to otherwise relatively innocuous inert particles; and (2) exposures of nonallergic pregnant females to inert or toxic environmental air particles can cause increased allergic susceptibility in offspring.

Figure 1.

Experimental protocols. (A) Particles exposure protocol. Normal females or pregnant mice were treated with diesel exhaust particle (DEP) or titanium dioxide (TiO₂) particle suspensions (50 ug/mouse) and analyzed 19 or 48 hours later. (B) Maternal particles exposure + single intraperitoneal neonatal sensitization period. Pregnant mothers at Day 14 of pregnancy (E14) received 50 μg/mouse intranasally of DEP, carbon black (CB), or TiO₂ particle suspensions or PBS buffer (negative control). Offspring of these mothers were injected once with 0.1 ml of 50 μg/ml ovalbumin (OVA) + alum (“suboptimal”) sensitization and challenged three times with 3% OVA aerosol.

Figure 2.

Direct analysis of bronchoalveolar lavage (BAL) responses in pregnant versus control females. Pregnant or normal mice were exposed to either DEP or TiO₂ particle suspension or PBS alone and BALs were obtained 48 hours later. Normal mice exposed to TiO₂ reveal minimal airway inflammation at 48 hours (A) after exposure. In contrast, pregnant mice reveal enhanced and prolonged inflammation seen even 48 hours after exposure to TiO₂ (B). Mean ± SEM (n > 9 each group). *P < 0.05.

Figure 3.

Inflammatory BAL response to LPS challenge. Pregnant mice or normal controls were exposed to LPS aerosol, and BALs were obtained 24 hours later. There is no significant difference in PMN counts in these groups. Mean ± SEM (n = 8).

Figure 4.

Serum cytokine levels after particle exposure. Pregnant (P) or normal (N) mice were exposed to either DEP or TiO₂ particle suspension and sera were obtained 48 hours later. Levels of proinflammatory cytokines are increased in pregnant mice compared with nonpregnant controls after both TiO₂ and DEP exposure (with P < 0.05). Mean ± SEM (n = 9 each group).

Figure 5.

Neonatal susceptibility in OVA protocol. Mother mice were exposed during pregnancy to 50 μg/mouse of either DEP or TiO₂, or 250 μg/mouse of CB particle suspension or PBS (Protocol 1B, Figure 1). Newborns were injected once with 0.1 ml of 50 μg/ml OVA plus alum and challenged three times with 3% OVA aerosol. Offspring of mice exposed during pregnancy to DEP showed increased airway hyperresponsiveness (AHR) seen as response to methacholine via whole-body plethysmography (Penh at 100 mg/ml Mch of 3.3±0.4) (A) and increased eosinophilic AI in BAL (B) as well as increased pulmonary infiltration (C, D), indicating that allergic susceptibility was induced. Surprisingly, neonates from mice exposed to “inert” TiO₂ and CB also showed similarly increased AHR (Penh at 100 mg/ml Mch of 2.8 ± 0.3 and 2.8 ± 0.3, respectively, versus 1.0 ± 0.2 in PBS controls, P < 0.05) (A). BAL eosinophilia was also increased (TiO₂ 13.6 ± 3.1% and CB 10.7 ± 1.2% versus 4.1 ± 1.0% in PBS controls) (B), as well as pulmonary inflammation (C, D). Mean ± SEM (n = 17–21 each group). *P < 0.05.