IgE-mediated rhesus monkey asthma: natural history and individual animal variation

A Novel Nonhuman Primate Model of Nonatopic Asthma

Nonhuman primate models have an essential role in understanding progressive respiratory disease pathogenesis. Immune and physiologic parameters in the nonhuman primate closely reflect the complexity of human systems and provide an exceptional translational impact for the investigation of the mucosal immune changes in response to environmental exposures. This potential warrants the development of novel models that will clarify the interaction of respiratory disease and the inhalable environment and the potential of novel therapies to alleviate the untoward results of these interactions. Nonhuman primate models of asthma can be spontaneous, induced, or experimentally manipulated by various exposures. Here we describe a model of exacerbation of airway hyperreactivity induced by exposure to an air pollutant, ozone, in a cohort of young adult asthmatic rhesus macaques.

Ozone-induced enhancement of airway hyperreactivity in rhesus macaques: Effects of antioxidant treatment

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.

Ascariasis as a model to study the helminth/allergy relationships

Ascariasis is the most frequent soil transmitted helminthiasis and, as well as other helminth infections, is expected to influence the clinical presentation of allergic diseases such as asthma. Indeed, several clinical and experimental works have shown an important impact either increasing or suppressing symptoms, and the same effects have been detected on the underlying immune responses. In this review we analyze the work on this field performed in Colombia, a Latin American tropical country, including aspects such as the molecular genetics of the IgE response to Ascaris; the allergenic activity of Ascaris IgE-binding molecular components and the immunological and clinical influences of ascariasis on asthma. The analysis allows us to conclude that the impact of ascariasis on the inception and evolution of allergic diseases such as asthma deserves more investigation, but advances have been made during the last years. The concurrent parasite-induced immunostimulatory and immunosuppressive effects during this helminthiasis do modify the natural history of asthma and some aspects of the practice of allergology in the tropics. Theoretically it can also influence the epidemiological trends of allergic diseases either by its absence or presence in different regions and countries.

Comparative immunology of allergic responses

Allergic responses occur in humans, rodents, non-human primates, avian species, and all of the domestic animals. These responses are mediated by immunoglobulin E (IgE) antibodies that bind to mast cells and cause release/synthesis of potent mediators. Clinical syndromes include naturally occurring asthma in humans and cats; atopic dermatitis in humans, dogs, horses, and several other species; food allergies; and anaphylactic shock. Experimental induction of asthma in mice, rats, monkeys, sheep, and cats has helped to reveal mechanisms of pathogenesis of asthma in humans. All of these species share the ability to develop a rapid and often fatal response to systemic administration of an allergen--anaphylactic shock. Genetic predisposition to development of allergic disease (atopy) has been demonstrated in humans, dogs, and horses. Application of mouse models of IgE-mediated allergic asthma has provided evidence for a role of air pollutants (ozone, diesel exhaust, environmental tobacco smoke) in enhanced sensitization to allergens.

New Allergens of Relevance in Tropical Regions: The Impact of Ascaris lumbricoides Infections

One of the many aspects of the relationships between parasite infections and allergic diseases is the possibility that allergens from parasites enhance the T_H2 responses, especially IgE production, in allergic diseases such as asthma. In this review we discuss about the allergenic composition of the nematode Ascaris lumbricoides and their potential impact on allergy sensitization and asthma pathogenesis and prevalence in populations living in the tropics and naturally exposed to both, mite allergens and helminth infections.

IgE cross-reactivity between Ascaris lumbricoides and mite allergens: possible influences on allergic sensitization and asthma

Nematode infections such as Ascariasis are important health problems in underdeveloped countries, most of them located in the tropics where environmental conditions also promote the perennial co-exposure to high concentrations of domestic mite allergens. Allergic diseases are common, and most of patients with asthma exhibit a predominant and strong IgE sensitization to mites. It is unknown whether co-exposure to Ascaris lumbricoides and the domestic mites Blomia tropicalis and Dermatophagoides pteronyssinus potentiates Th2 responses and IgE sensitization, thereby modifying the natural history of allergy. Recently, we obtained experimental evidence of a high cross-reactivity between the allergenic extracts of these invertebrates, involving well-known allergens such as tropomyosin and glutathione transferases. There is indirect evidence suggesting that the clinical impact of these findings may be important. In this review, we discuss the potential role of this cross-reactivity on several aspects of allergy in the tropics that have been a focus of a number of investigations, some of them with controversial results.

Interleukin-13 neutralization by two distinct receptor blocking mechanisms reduces immunoglobulin E responses and lung inflammation in cynomolgus monkeys

Interleukin (IL)-13 is a key cytokine driving allergic and asthmatic responses and contributes to airway inflammation in cynomolgus monkeys after segmental challenge with Ascaris suum antigen. IL-13 bioactivity is mediated by a heterodimeric receptor (IL-13Ralpha1/IL-4Ralpha) and can be inhibited in vitro by targeting IL-13 interaction with either chain. However, in cytokine systems, in vitro neutralization activity may not always predict inhibitory function in vivo. To address the efficacy of two different IL-13 neutralization mechanisms in a primate model of atopic disease, two humanized monoclonal antibodies to IL-13 were generated, with highly homologous properties, differing in epitope recognition. Ab01 blocks IL-13 interaction with IL-4Ralpha, and Ab02 blocks IL-13 interaction with IL-13Ralpha1. In a cynomolgus monkey model of IgE responses to A. suum antigen, both Ab01 and Ab02 effectively reduced serum titers of Ascaris-specific IgE and diminished ex vivo Ascaris-triggered basophil histamine release, assayed 8 weeks after a single administration of antibody. The two antibodies also produced comparable reductions in pulmonary inflammation after lung segmental challenge with Ascaris antigen. Increased serum levels of IL-13, lacking demonstrable biological activity, were seen postchallenge in animals given either anti-IL-13 antibody but not in control animals given human IgG of irrelevant specificity. These findings demonstrate a potent effect of IL-13 neutralization on IgE-mediated atopic responses in a primate system and show that IL-13 can be efficiently neutralized by targeting either the IL-4Ralpha-binding epitope or the IL-13Ralpha1-binding epitope.

Separation of bronchoconstriction from increased ventilatory drive in a nonhuman primate model of chronic allergic asthma

The relationship between allergen-induced ventilatory drive and bronchoconstriction was investigated in dust mite-sensitive cynomolgus macaques periodically exposed to low doses of aerosolized antigen for up to 5.5 yr. Initially, the animals responded to aerosolized dust mite allergen at a concentration of 350 arbitrary units (AU)/ml with simultaneous increases in lung resistance (RL) and respiratory rate (RR). With time, RL and RR became differentially sensitive to allergen provocation. At the end of the study period, aerosolized allergen at a concentration of 15 AU/ml doubled RR without increasing RL. When mechanically ventilated to maintain tidal volume, higher concentrations of allergen could be delivered, and RL increased. Inhaled disodium cromoglycate and intravenous diphenhydramine attenuated the increase in RR, indicating that allergen-induced release of histamine and activation of H(1) receptors mediated the response. Inhaled beta-adrenergic agonists attenuated the RR response to dust mite and to direct histamine provocation. These results demonstrate that chronic periodic allergen challenge increases the allergic sensitivity of histamine-dependent reflexes controlling ventilatory drive. Activation of these reflexes is independent of overt bronchoconstriction, but can be inhibited by beta-adrenergic agonists, indicating that beta-adrenergic agonists exert their effect independent of bronchodilation.

Dust mite-induced asthma in cynomolgus monkeys

Animal models exhibiting high homology with humans at the genetic and pathophysiological levels will facilitate identification and validation of gene targets underlying asthma. In the present study, a nonhuman primate model of allergic asthma was developed by sensitizing cynomolgus monkeys to dust mite antigen. Sensitization elevated allergen-specific serum IgE and IgG levels, and peripheral blood mononuclear cells isolated from sensitized animals released IL-4, IL-5, and IL-10, but not IFN-gamma. Aerosolized allergen decreased dynamic compliance and induced airway inflammation and hyperresponsiveness to aerosolized histamine. Albuterol and dexamethasone inhibited the airway constriction and allergen-induced inflammation, respectively. Airway wall remodeling that included goblet cell hyperplasia, basement membrane thickening, and smooth muscle hypertrophy was particularly evident in neonatally sensitized animals. In contrast to animals sensitized as adults, neonatally sensitized animals exhibited increased sensitivity to adenosine and larger allergen-induced changes in airway resistance and dynamic compliance. These results demonstrate that sensitization of cynomolgus monkeys with dust mite induces asthmalike symptoms, some of which may be dependent on age at the time of sensitization.

Toward developing a genome-wide microsatellite marker set for linkage analysis in the rhesus macaque (Macaca mulatta): identification of 76 polymorphic markers

Linkage analysis can be problematic in humans because of the lack of large, multigenerational pedigrees and the difficulties in obtaining phenotypic data on all family members. In contrast, large, captive colonies of rhesus macaque are a potentially valuable resource for linkage studies because detailed phenotypic and genealogical data are kept, inbreeding is avoided, and DNA samples can usually be obtained. Microsatellite marker sets for genome-wide screening are available in a number of species, but not for the rhesus macaque. We tested primers to 400 human microsatellite markers from a genome-wide mapping set using DNA from nine unrelated female rhesus macaques. We found that 76 (19%) of the primers amplified a polymorphic product using the standard protocols for human DNA. The average heterozygosity of the markers in humans was 0.80, compared to 0.65 in the rhesus macaques. This study provides preliminary data, which could be used toward the development of a linkage mapping set in this species. There would be a need, however, to confirm the Mendelian inheritance of the markers.

Animal models of asthma: potential usefulness for studying health effects of inhaled particles

Asthma is now recognized to be a chronic inflammatory disease that affects the whole lung. Incidence appears to be increasing despite improved treatment regimens. There is substantial epidemiological evidence suggesting a relationship between the incidence and severity of asthma (e.g., hospitalizations) and exposure to increased levels of air pollution, especially fine and ultrafine particulate material, in susceptible individuals. There have been a few studies in animal models that support this concept, but additional animal studies to test this hypothesis are needed. However, such studies must be performed with awareness of the strengths and weaknesses of the currently available animal models. For studies in mice, the most commonly used animal, a broad spectrum of molecular and immunological tools is available, particularly to study the balance between Th1 and Th2 responses, and inbred strains may be useful for genetic dissection of susceptibility to the disease. However, the mouse is a poor model for bronchoconstriction or localized immune responses that characterize the human disease. In contrast, allergic lung diseases in dogs and cats may more accurately model the human condition, but fewer tools are available for characterization of the mechanisms. Finally, economic issues as well as reagent availability limit the utility of horses, sheep, and primates.

T cell receptor-V beta repertoire in allergen-specific sensitization and increased airway responsiveness

An animal model system was developed to study the mechanisms resulting in allergic sensitization. Local allergen exposure via the airways and the lung stimulated an allergen-specific immunoglobulin E (IgE) response that was paralleled by the development of increased airway responsiveness (AR). It was found that CD4+ T cells of local draining lymph nodes played an important role in the regulation of these events. Stimulation of allergen-specific T cells requires interaction between major histocompatibility complex (MHC) class II molecules (expressed on antigen-presenting cells), peptide (presented on MHC) and the T cell receptor. Allergen sensitization stimulated T cells that expressed a restricted T cell receptor V beta (TCR-V beta) elements. Each allergen stimulated different V beta elements, and sensitization to the same allergen resulted in a different pattern of TCR-V beta stimulation in different lymphoid tissues. Some of these T cells had pro-allergenic effects, whereas others were able to inhibit the development of the allergic response, including the development of increased AR. These data indicate that the local T cell response regulates the type of immune response that evolves following local allergen sensitization.

The regulation of pulmonary immunity

No evidence has emerged which suggests that the principles of immunity derived from studies on cells from other body sites are contradicted in the lung and its associated lymphoid tissue. What is clear, however, is that the environment dictates the types of cells, their relationship to one another, and what perturbing events will set in motion either the development of an "active" immune response or tolerance. Investigating mechanisms for the development of lung immunity has increased our understanding of how human diseases develop and is continuing to suggest new ways to manipulate pulmonary immune responses. Demonstration that lung cells regulate both nonspecific inflammation and immunity through the expression of adhesion molecules and the secretion of cytokines offers hope for ways to design more effective vaccines, enhance microbial clearance in immunosuppressed hosts, and to suppress manifestations of immunologically mediated lung disease. Important lung diseases targeted for intensive research efforts in the immediate future are tuberculosis, asthma, and fibrotic lung disease. Perhaps even the common cold might be conquered. Considering the pace of current research on lung immunity, it may not be too ambitious to predict that these diseases may be conquered in the next decade.