Role of oxidative stress on diesel-enhanced influenza infection in mice.

Numerous studies have shown that air pollutants, including diesel exhaust (DE), reduce host defenses, resulting in decreased resistance to respiratory infections. This study sought to determine if DE exposure could affect the severity of an ongoing influenza infection in mice, and examine if this could be modulated with antioxidants. BALB/c mice were treated by oropharyngeal aspiration with 50 plaque forming units of influenza A/HongKong/8/68 and immediately exposed to air or 0.5 mg/m3 DE (4 hrs/day, 14 days). Mice were necropsied on days 1, 4, 8 and 14 post-infection and lungs were assessed for virus titers, lung inflammation, immune cytokine expression and pulmonary responsiveness (PR) to inhaled methacholine. Exposure to DE during the course of infection caused an increase in viral titers at days 4 and 8 post-infection, which was associated with increased neutrophils and protein in the BAL, and an early increase in PR. Increased virus load was not caused by decreased interferon levels, since IFN-ß levels were enhanced in these mice. Expression and production of IL-4 was significantly increased on day 1 and 4 p.i. while expression of the Th1 cytokines, IFN-γ and IL-12p40 was decreased. Treatment with the antioxidant N-acetylcysteine did not affect diesel-enhanced virus titers but blocked the DE-induced changes in cytokine profiles and lung inflammation. We conclude that exposure to DE during an influenza infection polarizes the local immune responses to an IL-4 dominated profile in association with increased viral disease, and some aspects of this effect can be reversed with antioxidants.

Modulation of pulmonary inflammatory responses and antimicrobial defenses in mice exposed to diesel exhaust.

Diesel exhaust (DE) is a major component of urban air pollution and has been shown to increase the severity of infectious and allergic lung disease. The purpose of this study was to evaluate the effects of DE exposure on pulmonary inflammation, mediator production and antimicrobial defenses in an exposure model that had previously been shown to increase susceptibility to influenza. BALB/c mice were exposed to filtered air, or to DE diluted to yield 0.5 or 2 mg/m(3) of diesel exhaust particles (DEP) for 4 h per day for 1 or 5 days. Immediately and 18 h after one or five diesel exposures mice were euthanized to assess both immediate and delayed effects. DE exposure for 5 days at either concentration caused higher neutrophil numbers and lesion scoring compared to air controls. Intracellular adhesion molecule-1 (ICAM-1), which recruits inflammatory cells and is an entry site for rhinoviruses was increased immediately after 1 or 5 days of DE exposure. Several inflammatory and immune cytokines (TNF-alpha, MIP-2, IL-6, IFN-gamma, and IL-13) were also upregulated at various time points and concentrations. In contrast, clara cell secretory protein (CCSP), surfactant protein A (SP-A), and surfactant protein D (SP-D) which are important host defense molecules, were significantly decreased at both the message and protein level with DE exposure. We conclude that exposure to moderate and high occupational levels of DE caused an increase in lung injury and inflammation, and a decrease in host defense molecules, which could result in increased susceptibility to respiratory pathogens.

Increased transcription of immune and metabolic pathways in naive and allergic mice exposed to diesel exhaust.

Diesel exhaust (DE) has been shown to enhance allergic sensitization in animals following high-dose instillation or chronic inhalation exposure scenarios. The purpose of this study was to determine if short-term exposures to diluted DE enhance allergic immune responses to antigen, and identify possible mechanisms using microarray technology. BALB/c mice were exposed to filtered air or diluted DE to yield particle concentrations of 500 or 2000 mug/m(3) 4 h/day on days 0-4. Mice were immunized intranasally with ovalbumin (OVA) antigen or saline on days 0-2, challenged on day 18 with OVA or saline, and all mice were challenged with OVA on day 28. Mice were necropsied either 4 h after the last DE exposure on day 4, or 18, 48, and 96 h after the last challenge. Immunological endpoints included OVA-specific serum IgE, biochemical and cellular profiles of bronchoalveolar lavage (BAL), and cytokine production in the BAL. OVA-immunized mice exposed to both concentrations of DE had increased eosinophils, neutrophils, lymphocytes, and interleukin-6 (high dose only) post-challenge compared with OVA control, whereas DE/saline exposure yielded increases in neutrophils at the high dose only. Transcriptional microarray analysis 4 h after the last DE exposure demonstrated distinct gene expression profiles for the high-dose DE/OVA and DE/saline groups. DE/OVA induced oxidative stress and metabolism pathways, whereas DE in the absence of immunization modulated cell cycle control, growth and differentiation, G-proteins, and cell adhesion pathways. This study shows for the first time early changes in gene expression induced by the combination of DE inhalation and mucosal immunization, which resulted in stronger development of allergic eosinophilia.

Diesel exhaust enhanced susceptibility to influenza infection is associated with decreased surfactant protein expression.

We have previously shown that exposure of respiratory epithelial cells to diesel exhaust (DE) enhances susceptibility to influenza infection and increases the production of interleukin (IL)-6 and interferon (IFN)-beta. The purpose of this study was to confirm and expand upon these in vitro results by assessing the effects of DE exposure on the progression of influenza infection and on development of associated pulmonary immune and inflammatory responses in vivo. BALB/c mice were exposed to air or to DE containing particulate matter at concentrations of 0.5 or 2 mg/m(3) for 4 h/day for 5 days and subsequently instilled with influenza A/Bangkok/1/79 virus. Exposure to 0.5 mg/m(3) (but not the higher 2-mg/m(3) dose) of DE increased susceptibility to influenza infection as demonstrated by a significant increase in hemagglutinin (HA) mRNA levels, a marker of influenza copies, and greater immunohistochemical staining for influenza virus protein in the lung. The enhanced susceptibility to infection observed in mice exposed to 0.5 mg/m(3) of DE was associated with a significant increase in the expression of IL-6, while antiviral lung IFN levels were unaffected. Analysis of the expression and production of surfactant proteins A and D, which are components of the interferon-independent antiviral defenses, showed that these factors were decreased following exposure to 0.5 mg/m(3) of DE but not to the higher 2-mg/m(3) concentration. Taken together, the results demonstrate that exposure to DE enhances the susceptibility to respiratory viral infections by reducing the expression and production of antimicrobial surfactant proteins.