MaryJane K. Selgrade

A Brief Targeted Review of Susceptibility Factors, Environmental Exposures, Asthma Incidence, and Recommendations for Future Asthma Incidence Research

Relative to research on effects of environmental exposures on exacerbation of existing asthma, little research on incident asthma and environmental exposures has been conducted. However, this research is needed to better devise strategies for the prevention of asthma. The U.S. Environmental Protection Agency (EPA) and National Institute of Environmental Health Sciences held a conference in October 2004 to collaboratively discuss a future research agenda in this area. The first three articles in this mini-monograph summarize the discussion on potential putative environmental exposure; they include an overview of asthma and conclusions of the workshop participants with respect to public health actions that could currently be applied to the problem and research needs to better understand and control the induction and incidence of asthma, the potential role of indoor/outdoor air pollutants in the induction of asthma), and biologics in the induction of asthma. Susceptibility is a key concept in the U.S. EPA “Asthma Research Strategy” document and is associated with the U.S. EPA framework of protecting vulnerable populations from potentially harmful environmental exposures. Genetics, age, and lifestyle (obesity, diet) are major susceptibility factors in the induction of asthma and can interact with environmental exposures either synergistically or antagonistically. Therefore, in this fourth and last article we consider a number of “susceptibility factors” that potentially influence the asthmatic response to environmental exposures and propose a framework for developing research hypotheses regarding the effects of environmental exposures on asthma incidence and induction.

Assessing The Health Effects and Risks Associated with Children's Inhalation Exposures—Asthma and Allergy

Adults and children may have different reactions to inhalation exposures due to differences in target tissue doses following similar exposures, and/or different stages in lung growth and development. In the case of asthma and allergy both the developing immune system and initial encounters with common allergens contribute to this differential susceptibility. Asthma, the most common chronic childhood disease, has significant public health impacts and is characterized by chronic lung inflammation, reversible airflow obstruction, and immune sensitization to allergens. Animal studies described here suggest that air pollutants exacerbate asthma symptoms and may also play a role in disease induction. Changes characteristic of asthma were observed in rhesus monkeys sensitized to house dust mite antigen (HDMA) as infants and exposed repeatedly thereafter to ozone (O3) and HDMA. O3 exposure compromised airway growth and development and exacerbated the allergen response to favor intermittent airway obstruction and wheeze. In Brown Norway rats a variety of air pollutants enhanced sensitization to HDMA such that symptoms elicited in response to subsequent allergen challenge were more severe. Although useful for assessing air pollutants effects on initial sensitization, the rodent immune system is immature at birth relative to humans, making this model less useful for studying differential effects between adults and children. Because computational models available to address childrens inhalation exposures are limited, default adjustments and their associated uncertainty will continue to be used in childrens inhalation risk assessment. Because asthma is a complex (multiple genes, phenotypes, organ systems) disease, this area is ripe for systems biology approaches.

Use of immunotoxicity data in health risk assessments: uncertainties and research to improve the process

A number of environmental contaminants can suppress immune responses and enhance susceptibility to infectious and/or neoplastic disease. Most of the evidence for immunotoxicity of such contaminants has been obtained from laboratory animal studies and risk assessors must make decisions about risk to the human population based on these studies. Uncertainties associated with this process include determining what level of immune suppression is adverse, extrapolating across species from rodent to human, and across levels of biologic organization from effects on immune function at the cellular level to effects on incidence of disease at the population level, accounting for intra-species variability, and assessing the relationship between effects following acute, subchronic, and chronic exposure. This paper reviews immunotoxicity data that may be applied to the development of risk assessment methods and models designed to reduce some of these uncertainties.

Evaluation of effects of ozone exposure on influenza infection in mice using several indicators of susceptibility

Mice were exposed to 1 ppm O3, 3 hr/day, for 5 consecutive days. Separate groups of mice were infected with influenza following each of the individual exposures. A twofold increase in the incidence of mortality and a 3-day decrease in mean survival time were observed in mice infected after the second exposure. There were no effects on percentage mortality or mean survival time due to exposure to 1 ppm O3 in mice infected after the first, third, fourth, or fifth exposure. When the exposure concentration was lowered to 0.5 ppm, there were no effects on mortality in mice infected after the second exposure. Five, daily, 3-hr exposures to 1 ppm O3 had no effect on virus titers in the lungs of mice infected after either the second or fifth exposure. In contrast, wet lung weights were significantly enhanced over infected air controls in mice infected after the second O3 exposure at both 1 and 0.5 ppm but not at 0.25 ppm exposure concentrations. This effect on lung wet weight was observed in mice infected with a dose of virus which produced 7-33% mortality in controls as well as in mice infected with a sublethal dose of virus. Histopathologic changes due to sublethal influenza infection, including nonsuppurative pneumonitis and necrosis, squamous metaplasia and hyperplasia of the epithelium lining the bronchi and bronchioles, were more severe in mice infected after the second of five, 1 ppm O3 exposure than in comparable air controls. Sublethal infection caused a loss of lung volume with secondary reduction in diffusing capability and homogenity of ventilation distribution. These latter two effects were also exacerbated in mice infected after the second of five, 1 ppm O3 exposures as compared to air controls. When mice were infected after the fifth, 1 ppm O3 exposure, there was no effect due to ozone on either lung wet weight or histopathology. The data indicate that O3 has little if any effect on antiviral defense mechanisms since virus titers in the lungs were not affected by O3 exposure. However, mortality and morbidity, as indicated by lung wet weights, histopathology, and pulmonary function changes, were enhanced by O3 exposure in mice infected after the second of five exposures suggesting that symptoms due to infection can be enhanced in the absence of enhanced virus replication, possibly due to synergistic effects of O3 and virus in production of lung pathology.(ABSTRACT TRUNCATED AT 400 WORDS)

Safety assessment of biotechnology products for potential risk of food allergy: implications of new research.

Food allergy is a potential risk associated with use of transgenic proteins in crops. Currently, safety assessment involves consideration of the source of the introduced protein, in silico amino acid sequence homology comparisons to known allergens, physicochemical properties, protein abundance in the crop, and, when appropriate, specific immunoglobulin E binding studies. Recently conducted research presented at an International Life Sciences Institute/Health and Environmental Sciences Institute-hosted workshop adds to the scientific foundation for safety assessment of transgenic proteins in five areas: structure/activity, serum screening, animal models, quantitative proteomics, and basic mechanisms. A web-based tool is now available that integrates a database of allergenic proteins with a variety of computational tools which could be used to improve our ability to predict allergenicity based on structural analysis. A comprehensive strategy and model protocols have been developed for conducting meaningful serum screening, an extremely challenging process. Several animal models using oral sensitization with adjuvant and one dermal sensitization model have been developed and appear to distinguish allergenic from non-allergenic food extracts. Data presented using a mouse model suggest that pepsin resistance is indicative of allergenicity. Certain questions remain to be addressed before considering animal model validation. Gel-free mass spectrometry is a viable alternative to more labor-intensive approaches to quantitative proteomics. Proteomic data presented on four nontransgenic varieties of soy suggested that if known allergen expression in genetically modified crops falls within the range of natural variability among commercial varieties, there appears to be no need to test further. Finally, basic research continues to elucidate the etiology of food allergy.

A murine model for low molecular weight chemicals: differentiation of respiratory sensitizers (TMA) from contact sensitizers (DNFB)

Exposure to low molecular weight (LMW) chemicals contributes to both dermal and respiratory sensitization and is an important occupational health problem. Our goal was to establish an in vivo murine model for hazard identification of LMW chemicals that have the potential to induce respiratory hypersensitivity (RH). We used a dermal sensitization protocol followed by a respiratory challenge with the evaluation of endpoints typically associated with RH in human disease. Trimellitic anhydride (TMA) was used as a prototype respiratory sensitizer and was compared to the dermal sensitizer; 2,4-dinitrofluorobenzene (DNFB), along with vehicle controls. BALB/c mice were dermally sensitized using two exposure protocols. Mice in both protocols were dermally exposed on experimental days; D-18 and D-17 (abdomen), and D-13 (ear). On D 0 mice received an intratracheal (IT) challenge. The mice in Protocol 2 were abdominally exposed twice with the addition of exposures on D-25 and D-24. Results indicate that mice required the additional dermal sensitization and the IT challenge (Protocol 2) to significantly elevate total IgE in serum and bronchoalveolar lavage fluid (BALF). Additional responses suggestive of RH were seen following Protocol 2, including increases in BALF cell numbers and neutrophils post IT with TMA (but not DNFB). These data suggest that the dermal sensitization and IT challenge followed by evaluation of serum antibodies and lung parameters are a reasonable and logistically feasible approach towards the development of a model for RH responses to LMW chemicals.

Allergen-triggered airway hyperresponsiveness and lung pathology in mice sensitized with the biopesticide Metarhizium anisopliae.

Metarhizium anisopliae is an entomopathogenic fungus recently licensed for indoor control of cockroaches, a major source of allergens. While M. anisopliae has been shown to be non-infectious and non-toxic to mammals there has been only limited research on potential allergenicity. Using a mouse model, we previously demonstrated allergic immune and inflammatory responses to this agent. The present study was designed to determine whether these responses were associated with changes in pulmonary responses, lung pathology, and the cytokine profile in bronchoalveolar lavage fluid (BALF). Soluble factors from fungal components were combined in equal protein amounts to form M. anisopliae crude antigen (MACA). BALB/C mice were intratracheally (i.t.) challenged with 10 microg MACA 14 days post intraperitoneal sensitization with 25 microg fungal antigen in aluminum hydroxide adjuvant. Physiological and cellular changes were examined. The mice were tested for airway hyperresponsiveness before (No Chal) and after (1, 3, and 8 days post challenge (DPIT)) MACA IT challenge. Subsequently, serum, BALF and the lungs were harvested. All treatment groups concurrently demonstrated significant non-specific pulmonary inflammation (neutrophil influx) and increased pulmonary sensitivity to methacholine (Mch) at 1 DPIT MACA challenge. Where as both adjuvant treated and naïve mice airway responses had returned to near normal levels by 3 DPIT, mice which were previously sensitized with MACA were still hyperresponsive to Mch challenge at 3 and 8 DPIT. This hyperresponsiveness correlates with eosinophil and lymphocyte influx, which is maximal at 3 DPIT and still elevated at 8 DPIT. Interleukin (IL) 5 was elevated for all treatment groups at 1 DPIT but only the MACA sensitized mice maintained elevated levels for both 3 and 8 DPIT. Furthermore, MACA sensitized mice had a more extensive inflammatory histopathology at all examined time points with peribronchial and perivascular infiltrates, like those associated with allergic responsiveness, peaking at 3 DPIT. These pulmonary pathologic changes appeared to be consistent with elevated levels of serum and BALF total IgE, BALF IL-4, eosinophils, and lymphocytes following MACA IT challenge in MACA sensitized mice. There were no significant differences among the three treatment groups with regard to BALF interferon (IFN) gamma. The cytokines profiled indicate a Th2-type response, which is reflected in the cellular influx and total IgE induction. These data further indicate that immune inflammatory responses, observed in mice following MACA sensitization and challenge, are associated with physiologic changes and histopathology characteristic of allergic disease.

Dietary vitamin A enhances sensitivity of the local lymph node assay

Murine assays such as the mouse ear swelling test (MEST) and the local lymph node assay (LLNA) are popular alternatives to guinea pig models for the identification of contact sensitizers, yet there has been concern over the effectiveness of these assays to detect weak and moderate sensitizers. Much work has been done to improve the sensitivity of the MEST, including the addition of a vitamin A acetate (VAA) enriched diet, which increases its sensitivity. Vitamin A acetate has been reported to increase the numbers of Langerhans cells (antigen presenting cells) in the skin, which could in turn enhance the cellular immune response. Because the LLNA relies on tritiated-thymidine incorporation by proliferating T cells during the induction phase, we have studied the potential of the VAA diet to enhance sensitivity of the LLNA. Results indicate that the VAA enriched diet significantly increased the LLNA sensitivity to formalin, eugenol, glutaraldehyde, trimellitic anhydride, and an azo dye at concentrations where no proliferation was observed in mice maintained on the standard diet. Maintenance on a VAA diet for 3 weeks prior to initiating the sensitization procedure was optimal. Thus, incorporation of a VAA diet improves the sensitivity of the LLNA as a quick, objective, and relatively inexpensive screen for detecting moderate and weak contact sensitizers.

Workshop on Status of Test Methods for Assessing Potential of Chemicals to Induce Respiratory Allergic Reactions

AbstractBecause of the association between allergy and asthma and the increasing incidence of morbidity and mortality due to asthma, there is growing concern over the potential of industrial chemicals to produce allergic reactions in the respiratory tract. Two classes of chemicals have been well studied in this area: diisocyanates and acid anhydrides. The Environmental Protection Agencys Office of Pollution Prevention and Toxics (OPPT) encounters such chemicals in their premanufacturing notice (PMN) program. This article is a summary of a workshop convened by OPPT in collaboration with EPAs Healtin Effects Research Laboratory to discuss presently available test methods that might be applied to potential chemical allergens during the PMN process, the types of chemicals that should be considered suspect, and the kinds of research and validation needed to improve our capability to make such predictions. Formal presentations by experts in the field summarized basic concepts associated with chemically mediat...

Comparison of the pathogenesis of murine cytomegalovirus in lung and liver following intraperitoneal or intratracheal infection.

This study compares the pathogenesis of murine cytomegalovirus (MCMV) infections following intraperitoneal (i.p.) and intratracheal (i.t.) inoculation. No deaths were seen in mice given 10(6) p.f.u. MCMV i.t., whereas 52% mortality occurred among animals given this dose i.p. This difference in mortality was not due to different effects on the lung, since virus titres in this organ on progressive days post-infection were similar for the two routes of inoculation and similar, minor histopathological changes were observed. In contrast, virus titres in the livers of mice inoculated i.p. were 100-fold higher than for those inoculated i.t., and histopathological changes were noticeably greater in the i.p. group. This suggests that the mortality seen following i.p. inoculation may have been due, at least in part, to effects of viral infection on liver function. Parallels between various forms of human cytomegalovirus infections and the types of infections seen following i.t. and i.p. infection with MCMV were observed.