Workshop to identify critical windows of exposure for children's health: immune and respiratory systems work group summary.

Abstract

Fetuses, infants, and juveniles (preadults) should not be considered simply "small adults" when it comes to toxicological risk. We present specific examples of developmental toxicants that are more toxic to children than to adults, focusing on effects on the immune and respiratory systems. We describe differences in both the pharmacokinetics of the developing immune and respiratory systems as well as changes in target organ sensitivities to toxicants. Differential windows of vulnerability during development are identified in the context of available animal models. We provide specific approaches to directly investigate differential windows of vulnerability. These approaches are based on fundamental developmental biology and the existence of discrete developmental processes within the immune and respiratory systems. The processes are likely to influence differential developmental susceptibility to toxicants, resulting in lifelong toxicological changes. We also provide a template for comparative research. Finally, we discuss the application of these data to risk assessment.

Early life second-hand smoke exposure and serious infectious morbidity during the first 8 years: evidence from Hong Kong’s “Children of 1997” birth cohort

“…In contrast, the impact on other infections, eg, meningococcal disease8 9 or allergic sensitisation,10 has been less well explored. It is biologically plausible that the early postnatal period represents a critical window of exposure as both alveolar proliferation and maturation of lymphocytes continue throughout early infancy 11. Evaluating the impact of SHS exposure at different ages on respiratory and other infections will help identify whether there are any critical periods for SHS exposure 12…”

Outdoor air pollution and infant mortality: analysis of daily time-series data in 10 English cities

“…6 The lung is not well developed at birth, 3 with 80% of alveoli being formed postnatally. 7 During the neonatal and post-neonatal periods, therefore, the developing lung is highly susceptible to environmental toxicants. [7][8][9] Associations between particulate matter ,10 mg/m 3 (PM 10 ) and infant mortality have been observed in time-series studies conducted in cities with notoriously high levels of pollution, such as Mexico City, 10 Seoul 11 and Sao Paulo.…”

Perinatal exposure to solvents and wheezing, eczema and food allergies at age 2

“…The exposure period (prenatal and postnatal) explored in this study is well known for its vulnerability (from the first weeks of pregnancy) to environmental factors that interfere with immune maturation 1. Previous work suggests that solvents may modify immune system development through T-cell polarisation toward the Th2 phenotype; this modification appears to promote type 1 hypersensitivity and thereby the occurrence of allergic disorders 21 32.…”

“…Many toxicants are known to affect airway development during this period of maturation 1 33 34. The consequences on the structure and the function of the respiratory system may be particularly strong during the third trimester of pregnancy and during the early postnatal period because of the development of pulmonary alveoli, the units of gas exchanges 2 33.…”

“…The prenatal and early childhood period is an important window of vulnerability for the developing immune and respiratory systems, both known to be very sensitive to environmental chemicals 1 2. Organic solvents, the immunotoxic properties of which have been shown in animal studies,3–5 are in widespread use in occupational and domestic settings.…”