Robert H. Lim

Maternal transmission of asthma risk.

Maternal asthma significantly increases the risk of asthma in offspring, but the mechanisms remain poorly defined. We review animal models used to study the maternal effect, focusing on a murine model developed in our laboratory. Mother mice rendered allergic to ovalbumin produce offspring that are more susceptible to allergic sensitization, seen as airway hyperresponsiveness and allergic airway inflammation after a sensitization protocol, which has minimal effects on newborns from normal mothers. Mechanistic analyses identify a role for interleukin‐4 (based on pre‐mating injection of neutralizing antibodies), dendritic cells and allergen‐specific T cells (based on adoptive transfer experiments). Other maternal exposures (e.g. pollutant exposure and non‐pulmonary allergy) can increase asthma susceptibility in offspring. This observation implies that the maternal transmission of asthma represents a final common pathway to various types of inflammatory stimuli. Identification of the shared molecular mechanisms in these models may allow better prevention and therapy. Current knowledge, gaps in knowledge and future directions are discussed.

Prenatal maternal stress predicts childhood asthma in girls: project ice storm.

Little is known about how prenatal maternal stress (PNMS) influences risks of asthma in humans. In this small study, we sought to determine whether disaster-related PNMS would predict asthma risk in children. In June 1998, we assessed severity of objective hardship and subjective distress in women pregnant during the January 1998 Quebec Ice Storm. Lifetime asthma symptoms, diagnoses, and corticosteroid utilization were assessed when the children were 12 years old (N = 68). No effects of objective hardship or timing of the exposure were found. However, we found that, in girls only, higher levels of prenatal maternal subjective distress predicted greater lifetime risk of wheezing (OR = 1.11; 90% CI = 1.01–1.23), doctor-diagnosed asthma (OR = 1.09; 90% CI = 1.00–1.19), and lifetime utilization of corticosteroids (OR = 1.12; 90% CI = 1.01–1.25). Other perinatal and current maternal life events were also associated with asthma outcomes. Findings suggest that stress during pregnancy opens a window for fetal programming of immune functioning. A sex-based approach may be useful to examine how prenatal and postnatal environments combine to program the immune system. This small study needs to be replicated with a larger, more representative sample.

Maternal stress during pregnancy increases neonatal allergy susceptibility: Role of glucocorticoids

We sought to test experimentally whether maternal stress can promote susceptibility to development of asthma-like allergic airways disease in offspring. Normal pregnant mice (day 15) were subjected to a single restraint stress exposure. We subsequently tested their offspring for the development of airway hyperreactivity (AHR) and allergic airway inflammation (AI), after an intentionally suboptimal sensitization protocol. The offspring of stressed mothers showed levels of AI and enhanced airway responses to methacholine comparable to those seen in fully sensitized and challenged positive control animals; in contrast, minimal effects were seen in control offspring. Restraint stress caused a rapid and large increase in plasma corticosterone levels. Maternal treatment with dexamethasone on day 15 of pregnancy mimicked the stress effect and reproduced the AI and AHR outcomes, whereas blockade of the stress-induced corticosterone surge with metyrapone pretreatment of pregnant mice abrogated the effect. We conclude that stress-triggered glucocorticoids during pregnancy can increase susceptibility to allergy in offspring. Because inflammation typically includes a stress hormone response, the results also suggest a common pathway by which various injurious exposures during pregnancy might increase offspring susceptibility to asthma.

REVIEW ARTICLE: Maternal Transmission of Asthma Risk

Maternal asthma significantly increases the risk of asthma in offspring, but the mechanisms remain poorly defined. We review animal models used to study the maternal effect, focusing on a murine model developed in our laboratory. Mother mice rendered allergic to ovalbumin produce offspring that are more susceptible to allergic sensitization, seen as airway hyperresponsiveness and allergic airway inflammation after a sensitization protocol, which has minimal effects on newborns from normal mothers. Mechanistic analyses identify a role for interleukin‐4 (based on pre‐mating injection of neutralizing antibodies), dendritic cells and allergen‐specific T cells (based on adoptive transfer experiments). Other maternal exposures (e.g. pollutant exposure and non‐pulmonary allergy) can increase asthma susceptibility in offspring. This observation implies that the maternal transmission of asthma represents a final common pathway to various types of inflammatory stimuli. Identification of the shared molecular mechanisms in these models may allow better prevention and therapy. Current knowledge, gaps in knowledge and future directions are discussed.

Maternal allergic contact dermatitis causes increased asthma risk in offspring.

BackgroundOffspring of asthmatic mothers have increased risk of developing asthma, based on human epidemiologic data and experimental animal models. The objective of this study was to determine whether maternal allergy at non-pulmonary sites can increase asthma risk in offspring.MethodsBALB/c female mice received 2 topical applications of vehicle, dinitrochlorobenzene, or toluene diisocyanate before mating with untreated males. Dinitrochlorobenzene is a skin-sensitizer only and known to induce a Th1 response, while toluene diisocyanate is both a skin and respiratory sensitizer that causes a Th2 response. Both cause allergic contact dermatitis. Offspring underwent an intentionally suboptimal protocol of allergen sensitization and aerosol challenge, followed by evaluation of airway hyperresponsiveness, allergic airway inflammation, and cytokine production. Mothers were tested for allergic airway disease, evidence of dermatitis, cellularity of the draining lymph nodes, and systemic cytokine levels. The role of interleukin-4 was also explored using interleukin-4 deficient mice.ResultsOffspring of toluene diisocyanate but not dinitrochlorobenzene-treated mothers developed an asthmatic phenotype following allergen sensitization and challenge, seen as increased Penh values, airway inflammation, bronchoalveolar lavage total cell counts and eosinophilia, and Th2 cytokine imbalance in the lung. Toluene diisocyanate treated interleukin-4 deficient mothers were able to transfer asthma risk to offspring. Mothers in both experimental groups developed allergic contact dermatitis, but not allergic airway disease.ConclusionMaternal non-respiratory allergy (Th2-skewed dermatitis caused by toluene diisocyanate) can result in the maternal transmission of asthma risk in mice.

Transplacental passage of interleukins 4 and 13

The mechanisms by which prenatal events affect development of adult disease are incompletely characterized. Based on findings in a murine model of maternal transmission of asthma risk, we sought to test the role of the pro-asthmatic cytokines interleukin IL-4 and -13. To assess transplacental passage of functional cytokines, we assayed phosphorylation of STAT-6, a marker of IL-4 and -13 signaling via heterodimeric receptor complexes which require an IL-4 receptor alpha subunit. IL-4 receptor alpha−/− females were mated to wild-type males, and pregnant females were injected with supraphysiologic doses of IL-4 or 13. One hour after injection, the receptor heterozygotic embryos were harvested and tissue nuclear proteins extracts assayed for phosphorylation of STAT-6 by Western blot. While direct injection of embryos produced a robust positive control, no phosphorylation was seen after maternal injection with either IL-4 or -13, indicating that neither crossed the placenta in detectable amounts. The data demonstrate a useful approach to assay for transplacental passage of functional maternal molecules, and indicate that molecules other than IL-4 and IL-13 may mediate transplacental effects in maternal transmission of asthma risk.

Gender Differences in Asthma

Publisher Summary Asthma is a major public health problem. It remains a very common cause of substantial morbidity and occasional mortality. The diagnosis is usually made on the basis of symptom history, clinical exam, and pulmonary function testing. The defining pathology of this chronic disease of the airways is allergic inflammation. The inflammatory response involves abundant eosinophils, as well as multiple other cell types including mast cells, lymphocytes, and neutrophils. However, the precise relationship of the many pathogenic cells and mediators to specific signs or symptoms is complex and remains the subject of active research. There are important gender differences in asthma. A core observation in many epidemiologic studies is that asthma prevalence differs depending on sex and age. In the pre-pubertal population, asthma is more common in boys compared to girls. After puberty, the gender ratio shifts to favor females. The magnitude of this gender difference is perhaps best described as modest (post-pubertal male vs. female odds ratio 0.8, or 44.4d% of males with current asthma were diagnosed at 18 years or older vs. 63.9% for females). However, given the large number of asthmatics (e.g. approximately 10% of the population), these percentage shifts have considerable impact. The basis for these gender effects remains incompletely understood, but significant progress has been made. A clearer understanding of the mechanisms behind this phenomenon will allow for better care of asthmatic patients. This chapter first reviews the clinical and epidemiologic data concerning gender differences in asthma, and then examines the literature regarding potential mechanisms. The potential etiologies examined include developmental differences, estrogens, progesterone, and androgens.

REVIEW ARTICLE: Maternal Transmission of Asthma Risk: MATERNAL TRANSMISSION OF ASTHMA RISK

Maternal asthma significantly increases the risk of asthma in offspring, but the mechanisms remain poorly defined. We review animal models used to study the maternal effect, focusing on a murine model developed in our laboratory. Mother mice rendered allergic to ovalbumin produce offspring that are more susceptible to allergic sensitization, seen as airway hyperresponsiveness and allergic airway inflammation after a sensitization protocol, which has minimal effects on newborns from normal mothers. Mechanistic analyses identify a role for interleukin‐4 (based on pre‐mating injection of neutralizing antibodies), dendritic cells and allergen‐specific T cells (based on adoptive transfer experiments). Other maternal exposures (e.g. pollutant exposure and non‐pulmonary allergy) can increase asthma susceptibility in offspring. This observation implies that the maternal transmission of asthma represents a final common pathway to various types of inflammatory stimuli. Identification of the shared molecular mechanisms in these models may allow better prevention and therapy. Current knowledge, gaps in knowledge and future directions are discussed.