Viral infections, cytokine dysregulation and the origins of childhood asthma and allergic diseases.

BACKGROUND: The origins of asthma and allergic disease begin in early life for many individuals. It is vital to understand the factors and/or events leading to their development. METHODS: The Childhood Origins of Asthma project evaluated children at high risk for asthma to study the relationships among viral infections, environmental factors, immune dysregulation, genetic factors, and the development of atopic diseases. Consequently wheezing illnesses, viral respiratory pathogen identification, and in vitro cytokine response profiles were comprehensively evaluated from birth to 3 years of age, and associations of the observed phenotypes with genetic polymorphisms were investigated. RESULTS: For the entire cohort, cytokine responses did not develop according to a strict T helper cell 1 or T helper cell 2 polarization pattern during infancy. Increased cord blood mononuclear cell phytohemagglutin-induced interferon-gamma responses of mononuclear cells were associated with decreased numbers of moderate to severe viral infections during infancy, especially among subjects with the greatest exposure to other children. In support of the hygiene hypothesis, an increased frequency of viral infections in infancy resulted in increased mitogen-induced interferon-gamma responses at 1 year of age. First year wheezing illnesses caused by respiratory viral infection were the strongest predictor of subsequent third year wheezing. Also, genotypic variation interacting with environmental factors, including day care, was associated with clinical and immunologic phenotypes that may precede the development of asthma. CONCLUSIONS: Associations between clinical wheezing, viral identification, specific cytokine responses and genetic variation provide insight into the immunopathogenesis of childhood asthma and allergic diseases.

Rhinovirus illnesses during infancy predict subsequent childhood wheezing.

BACKGROUND: The contribution of viral respiratory infections during infancy to the development of subsequent wheezing and/or allergic diseases in early childhood is not established. OBJECTIVE: To evaluate these relationships prospectively from birth to 3 years of age in 285 children genetically at high risk for developing allergic respiratory diseases. METHODS: By using nasal lavage, the relationship of timing, severity, and etiology of viral respiratory infections during infancy to wheezing in the 3rd year of life was evaluated. In addition, genetic and environmental factors that could modify risk of infections and wheezing prevalence were analyzed. RESULTS: Risk factors for 3rd year wheezing were passive smoke exposure (odds ratio [OR]=2.1), older siblings (OR=2.5), allergic sensitization to foods at age 1 year (OR=2.0), any moderate to severe respiratory illness without wheezing during infancy (OR=3.6), and at least 1 wheezing illness with respiratory syncytial virus (RSV; OR=3.0), rhinovirus (OR=10) and/or non-rhinovirus/RSV pathogens (OR=3.9) during infancy. When viral etiology was considered, 1st-year wheezing illnesses caused by rhinovirus infection were the strongest predictor of subsequent 3rd year wheezing (OR=6.6; P < .0001). Moreover, 63% of infants who wheezed during rhinovirus seasons continued to wheeze in the 3rd year of life, compared with only 20% of all other infants (OR=6.6; P < .0001). CONCLUSION: In this population of children at increased risk of developing allergies and asthma, the most significant risk factor for the development of preschool childhood wheezing is the occurrence of symptomatic rhinovirus illnesses during infancy that are clinically and prognostically informative based on their seasonal nature.

Effects of dog ownership and genotype on immune development and atopy in infancy.

BACKGROUND: Exposure to furred pets might confer protection against the development of allergic sensitization through a mechanism that is incompletely understood. OBJECTIVE: The objective of this study was to determine the effects of pet exposure and genotype on immunologic development and the incidence of atopic markers and diseases in the first year of life. METHODS: Pet exposure in the home was compared with cytokine secretion patterns (mitogen-stimulated mononuclear cells at birth and age 1 year) and indicators of atopy (allergen-specific and total IgE, eosinophilia, food allergy, atopic dermatitis) in 285 infants. Interactions with genotype at the CD14 locus were also evaluated in the data analyses. RESULTS: Exposure to dogs was associated with reduced allergen sensitization (19% vs 33%, P =.020) and atopic dermatitis (30% vs 51%, P <.001). The risk for atopic dermatitis was further influenced by genotype at the CD14 locus (P =.006), even after adjusting for exposure to dogs (P =.003). Furthermore, infants with the genotype -159TT were less likely to develop atopic dermatitis if they were exposed to a dog (5% vs 43%, P =.04). Last, dog exposure was associated with increased IL-10 (117 vs 79 pg/mL, P =.002) and IL-13 (280 vs 226 pg/mL, P =.013) responses at age 1 year. CONCLUSIONS: Having a dog in infancy is associated with higher IL-10 and IL-13 cytokine secretion profiles and reduced allergic sensitization and atopic dermatitis. These findings suggest that postnatal exposure to dogs can influence immune development in a genotype-specific fashion and thereby attenuate the development of atopy in at-risk children.

Developmental cytokine response profiles and the clinical and immunologic expression of atopy during the first year of life.

BACKGROUND: Allergic diseases have been linked to abnormal patterns of immune development, and this has stimulated efforts to define the precise patterns of cytokine dysregulation that are associated with specific atopic phenotypes. OBJECTIVE: Cytokine-response profiles were prospectively analyzed over the first year of life and compared with the clinical and immunologic expressions of atopy. METHODS: Umbilical cord and 1-year PBMCs were obtained from 285 subjects from allergic families. PHA-stimulated cytokine-response profiles (IL-5, IL-10, IL-13, and IFN-gamma) were compared with blood eosinophil counts and total and specific IgE levels (dust mites, cat, egg, Alternaria species, peanut, milk, and dog) at age 1 year and at the development of atopic dermatitis and food allergy. RESULTS: For the cohort as a whole, cytokine responses did not evolve according to a strict TH1 or TH2 polarization pattern. PHA-stimulated cord blood cells secreted low levels of IL-5 (2.1 pg/mL), moderate levels of IFN-gamma (57.4 pg/mL), and greater amounts of IL-13 (281.8 pg/mL). From birth to 1 year, IL-5 responses dramatically increased, whereas IL-13 and IFN-gamma responses significantly decreased. Reduced cord blood secretion of IL-10 and IFN-gamma was associated with subsequent sensitization to egg. In addition, there was evidence of TH2 polarization (increased IL-5 and IL-13 levels) associated with blood eosinophilia and increased total IgE levels by age 1 year. CONCLUSION: These findings demonstrate that cytokine responses change markedly during the first year of life and provide further evidence of a close relationship between TH2 skewing of immune responses and the incidence of atopic manifestations in children.

Relationships among specific viral pathogens, virus-induced interleukin-8, and respiratory symptoms in infancy.

Both virus-mediated damage to airway tissues and induction of pro-inflammatory cytokines such as interleukin-8 (IL-8) could contribute to symptom severity during viral respiratory infections in children. To test the hypothesis that IL-8 contributes to the pathogenesis of respiratory symptoms during naturally acquired respiratory viral infections in children, nasal wash samples collected from infants with acute viral infections (n = 198) or from healthy uninfected infants (n = 31) were analysed for IL-8. Nasal wash IL-8 was positively related to age in uninfected children (rs = 0.36, p < 0.05). Respiratory syncytial virus (RSV) infection caused more severe respiratory symptoms compared to infections with influenza A, parainfluenza viruses, or rhinoviruses. In addition, RSV, parainfluenza and rhinovirus infections increased levels of IL-8 in nasal lavage fluid, and there were some differences in the ability of the viruses to induce IL-8 production (RSV>influenza, p < 0.05). Finally, there were significant correlations between nasal wash IL-8 levels and symptom scores during infections with rhinovirus (rs = 0.56, p < 0.001) or influenza A (rs = 0.45, p < 0.05), but not with parainfluenza virus or RSV. These findings provide evidence of a close relationship between the generation of IL-8 and symptoms during acute community-acquired infections with rhinovirus or influenza A. In contrast, for RSV and parainfluenza infections, factors in addition to IL-8 production appear to contribute to the generation of clinical symptoms.