Prenatal origins of asthma and allergy

Mast cell ontogeny: From fetal development to life-long health and disease

Mast cells (MCs) are evolutionarily ancient innate immune cells with important roles in protective immunity against bacteria, parasites, and venomous animals. They can be found in most organs of the body, where they also contribute to normal tissue functioning, for example by engaging in crosstalk with nerves. Despite this, they are most widely known for their detrimental roles in allergy, anaphylaxis, and atopic disease. Just like macrophages, mast cells were conventionally thought to originate from the bone marrow. However, they are already present in fetal tissues before the onset of bone marrow hematopoiesis, questioning this dogma. In recent years, our view of myeloid cell ontogeny has been revised. We now know that the first mast cells originate from progenitors made in the extra-embryonic yolk sac, and later get supplemented with mast cells produced from subsequent waves of hematopoiesis. In most connective tissues, sizeable populations of fetal-derived mast cells persist into adulthood, where they self-maintain largely independently from the bone marrow. These developmental origins are highly reminiscent of macrophages, which are known to have critical functions in development. Mast cells too may thus support healthy development. Their fetal origins and longevity also make mast cells susceptible to genetic and environmental perturbations, which may render them pathological. Here, we review our current understanding of mast cell biology from a developmental perspective. We first summarize how mast cell populations are established from distinct hematopoietic progenitor waves, and how they are subsequently maintained throughout life. We then discuss what functions mast cells may normally have at early life stages, and how they may be co-opted to cause, worsen, or increase susceptibility to disease.

Antenatal steroid therapy for fetal lung maturation and the subsequent risk of childhood asthma: a longitudinal analysis

This study was designed to test the hypothesis that fetal exposure to corticosteroids in the antenatal period is an independent risk factor for the development of asthma in early childhood with little or no effect in later childhood. A population-based cohort study of all pregnant women who resided in Nova Scotia, Canada, and gave birth to a singleton fetus between 1989 and 1998 was undertaken. After a priori specified exclusions, 80,448 infants were available for analysis. Using linked health care utilization records, incident asthma cases developed after 36 months of age were identified. Extended Cox proportional hazards models were used to estimate hazard ratios while controlling for confounders. Exposure to corticosteroids during pregnancy was associated with a risk of asthma in childhood between 3–5 years of age: adjusted hazard ratio of 1.19 (95% confidence interval: 1.03, 1.39), with no association noted after 5 years of age: adjusted hazard ratio for 5–7 years was 1.06 (95% confidence interval: 0.86, 1.30) and for 8 or greater years was 0.74 (95% confidence interval: 0.54, 1.03). Antenatal steroid therapy appears to be an independent risk factor for the development of asthma between 3 and 5 years of age.

Fetal growth and hospitalization with asthma during early childhood: a follow-up study in Denmark

BACKGROUND

Childhood asthma may have a fetal origin. In order to examine this hypothesis we examined the association between fetal growth indicators and hospitalization with asthma during early childhood.

METHODS

We performed a cohort study with 10 440 children whose mothers attended the midwife centres in Odense and Aalborg, Denmark, from April 1984 to April 1987 at approximately the 36th week of gestation. Information on hospitalization with asthma was extracted from the National Hospital Discharge Registry, which allowed a complete follow-up of all members of the cohort who remained alive and residents in the county.

RESULTS

The cumulative incidence rates of hospitalization with 'definite' and 'any' asthma were 3.5% and 5.0%, respectively, at 12 years of age. After adjusting for potential confounders, there were increased trends in the risk of asthma hospitalization with birthweight and ponderal index. More pronounced trends, particularly in the risk of definite asthma, were found among children of over the average birthweight (IRR = 1.62, 95% CI: 1.02-2.59 per 1000 g increase) or ponderal index (IRR = 1.06, 95% CI: 1.02-1.10 per 0.1 g/cm(3) increase). However, the increased risk in large babies was seen only in children with a ponderal index of > or =2.5 g/cm3.

CONCLUSION

Birthweight and ponderal index were associated with childhood asthma indicated by hospitalization. Fetal growth itself, determinants of fetal growth, or any unadjusted factors that correlate with fetal growth, could cause the association.