Low-grade disease activity in early life precedes childhood asthma and allergy.

Asthma and allergies are today the most common chronic diseases in children and the leading causes of school absences, chronic medication usage, emergency department visits and hospitalizations, which affect all members of the family and represent a significant societal and scientific challenge. These highly prevalent disorders are thought to originate from immune distortion in early childhood, but the etiology and heterogeneity of the disease mechanisms are not understood, which hampers preventive initiatives and makes treatment inadequate. The objective of this thesis is to investigate the presence of an early life disease activity prior to clinical symptoms to understand the anteceding pathophysiological steps towards childhood asthma and allergy. The thesis is built on seven studies from the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC2000) birth cohort examining biomarkers of disease activity in 411 asymptomatic neonates in cord blood (I-II), urine (III), exhaled breath (IV-V) and infant lung function (VI-VII) in relation to the subsequent development of asthma and allergy during the first seven years of life. In papers I-II, we studied cord blood chemokines and 25(OH)-vitamin D, which represent a proxy of the inborn immature immune system, the intrauterine milieu, and the maternal immune health during pregnancy. High levels of the Th2-related chemokine CCL22 and high CCL22/CXCL11 ratio were positively correlated with total IgE level during preschool age (II). This suggests an inborn Th2 skewing of the immune system in healthy newborns subsequently developing elevated total IgE antibodies, which is considered to increase the risk of asthma and allergies later in life. Additionally, deficient cord blood 25(OH)-vitamin D levels were associated with a 2.7-fold increased risk of recurrent wheeze at age 0-7 years (I). Together, these findings support the concept that early life immune programming in the pre-symptomatic era plays an essential role for promotion of or protection against asthma and allergies. Therefore, preventive initiatives to restore immune health, such as vitamin D supplementation, should be directed to the fetus and the earliest postnatal life. The eosinophil granulocyte has a major role in the allergic inflammatory cascade and eosinophilia is considered a hallmark of many allergic phenotypes. In paper III, we examined neonatal urinary biomarkers including eosinophil protein X (u-EPX), which is contained in the eosinophil granules. Elevated u-EPX in asymptomatic neonates was associated with development of allergic sensitization and nasal eosinophilia, but not with wheezing or asthma (III). These findings suggest the presence of an ongoing low-grade disease process in early life characterized by eosinophil activation prior to appearance of allergy-related conditions. In papers IV-V, we investigated perinatal and genetic predictors of neonatal fractional exhaled nitric oxide (FeNO) and the relationship between neonatal FeNO and wheezing later in child-hood. The a priori selected determinants encompassed asthma genetic risk variants, anthropometrics, demographics, socioeconomics, parental asthma and allergy, maternal smoking, paracetamol and antibiotic usage during pregnancy, and neonatal bacterial airway colonization. Among those, only the DENND1B risk allele and paternal history of asthma and allergy were associated with increased FeNO values (V) suggesting that raised FeNO in neonatal life is primarily an inherited trait. The neonatal FeNO levels were widely dispersed (1-67 ppb) and children with values in the upper quartile were at increased risk of recurrent wheezing in early childhood, but not persistent wheezing, reduced lung function or allergy-related endpoints (IV). This suggests that elevated neonatal FeNO represents an early asymptomatic low-grade disease process other than congenitally small airway calibre contributing to a transient wheezing phenotype. Reduced lung function in neonates is associated with wheezing and asthma proneness, but it is unknown if such host factor also confers a risk of acute bronchiolitis, which is considered an index event of asthma persisting into school age. In paper VI, we investigated neonatal forced flow, volume, and responsiveness to methacholine in relation to occurrence of acute severe bronchiolitis at age 0-2 years. Children developing bronchiolitis had a 2.5-fold increased bronchial responsiveness as neonates (VI) suggesting a preexisting joint propensity of the airways to react adversely to common respiratory viruses and to develop asthma. This finding proposes airway hyperresponsiveness as yet another marker of low-grade disease activity among asymptomatic neonates on a trajectory towards childhood asthma. In paper VII, we examined whether neonates with impaired pulmonary capacity also had signs of systemic inflammation prior to clinical symptoms. Reduced FEV0.5 was significantly associated with elevated serum hs-CRP and other blood inflammatory markers (VII) suggesting presence of systemic low-grade inflammation from the beginning of life. Chronic low-grade inflammation is a common nominator of virtually all the major non-communicable welfare diseases (NCDs) of modernity whereof asthma and allergies are the earliest debuting disorders. The novel finding of systemic low-grade inflammation among neonates at increased risk of asthma and allergy, therefore implies that exploring the origins of asthma and allergy may also unravel disease mechanisms involved in other NCDs. In conclusion, the series of papers presented in this thesis (I-VII) evidence the presence of a pre-symptomatic disease process measurable in several body compartments, which supports the notion of low-grade disease activity in early life as a generic trait among neonates developing asthma and allergy. This hypothesis piggybacking on single biomarker assessments could be enforced and refined by applying novel global omics approaches. In particular, metabolomic analyses of serum, urine, and airway lining fluid from neonates as well as neonatal VOC profiling of exhaled breath may facilitate a broader understanding of the early low-grade disease activity preceding clinical symptoms. Disentangling the introductory pathophysiological mechanisms and underlying endotypes of disease is paramount for generating successful preventive measures to alleviate the major global burden of asthma, allergy, and other NCDs of modern time.

Susceptibility to Lower Respiratory Infections in Childhood is Associated with Perturbation of the Cytokine Response to Pathogenic Airway Bacteria.

BACKGROUND: Neonatal colonization of the airways with respiratory pathogens is associated with increased risk of lower respiratory infections (LRI) in early childhood. Therefore, we hypothesized that children developing LRI have an aberrant immune response to pathogenic bacteria in infancy. The objective was to characterize in vitro the early life systemic immune response to pathogenic bacteria and study the possible association with incidence of LRI during the first 3 years of life. METHODS: The Copenhagen Prospective Studies on Asthma in Childhood2000 (COPSAC2000) is a clinical birth cohort study of 411 children born of mothers with asthma. LRI incidence was prospectively captured from 6-monthly planned visits and visits at acute respiratory episodes. The in vitro systemic immune response to Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae was characterized by the production of TNF-α, IFN-γ, IL-2, IL-5, IL-10, IL-13 and IL-17 in peripheral blood mononuclear cells isolated at age 6 months from 291 infants. Data were analyzed by Poisson regression against incidence of LRI in infancy. RESULTS: A multivariable model including all cytokine responses from the 3 different bacterial stimulations significantly identified children at risk of LRI (P = 0.006). The immune response pattern associated with LRI was characterized by perturbed production of several cytokines rather than production of one specific cytokine, and was independent of concurrent asthma. TNF-α and IL-5 were key drivers but did not explain the entire variation in LRI susceptibility. CONCLUSIONS: Children at risk of future LRI present a perturbed systemic immune response upon exposure to common airway pathogens in early life.

Fraction of exhaled nitric oxide and bronchial responsiveness are associated and continuous traits in young children independent of asthma.

BACKGROUND: Elevated fraction of exhaled nitric oxide (FENO) and bronchial hyperresponsiveness are used as surrogate markers of asthma. These traits may be continuous in the population. The objective of this study was to investigate whether FENO and bronchial responsiveness are associated in both children with and children without a history of asthma symptoms. METHODS: One hundred ninety-six 6-year-old children with no asthma symptoms, intermittent asthma symptoms, and persistent asthma were randomly included from the Copenhagen Prospective Study on Asthma in Childhood prospective clinical birth cohort of mothers with asthma. Bronchial responsiveness was assessed as the relative change in specific airway resistance after cold dry air hyperventilation. FENO measurements were performed prior to the hyperventilation test. The association between FENO and bronchial responsiveness was assessed by generalized linear models. RESULTS: Bronchial responsiveness and FENO exhibited a significant and linear association in the population. A doubling of FENO corresponded to an 8.4% (95% CI, 3.7%-13.1%; P = .0006) increase in airway resistance after challenge testing and remained significant after adjustment for sex, allergic rhinitis, current asthma, inhaled corticosteroid treatment, and upper respiratory tract infections prior to testing. Stratified analyses showed similar associations in children with and without asthma. CONCLUSIONS: FENO and bronchial responsiveness are associated and continuous traits in young children regardless of asthma symptoms, suggesting a continuous subclinical to clinical process underlying asthma. The findings also suggest caution against the use of these surrogate markers for a dichotomized approach to asthma diagnosis.

Common variants at 12q15 and 12q24 are associated with infant head circumference.

To identify genetic variants associated with head circumference in infancy, we performed a meta-analysis of seven genome-wide association studies (GWAS) (N = 10,768 individuals of European ancestry enrolled in pregnancy and/or birth cohorts) and followed up three lead signals in six replication studies (combined N = 19,089). rs7980687 on chromosome 12q24 (P = 8.1 × 10(-9)) and rs1042725 on chromosome 12q15 (P = 2.8 × 10(-10)) were robustly associated with head circumference in infancy. Although these loci have previously been associated with adult height, their effects on infant head circumference were largely independent of height (P = 3.8 × 10(-7) for rs7980687 and P = 1.3 × 10(-7) for rs1042725 after adjustment for infant height). A third signal, rs11655470 on chromosome 17q21, showed suggestive evidence of association with head circumference (P = 3.9 × 10(-6)). SNPs correlated to the 17q21 signal have shown genome-wide association with adult intracranial volume, Parkinson's disease and other neurodegenerative diseases, indicating that a common genetic variant in this region might link early brain growth with neurological disease in later life.

Reduced diversity of the intestinal microbiota during infancy is associated with increased risk of allergic disease at school age.

BACKGROUND: Changes in the human microbiome have been suggested as a risk factor for a number of lifestyle-related disorders, such as atopic diseases, possibly through a modifying influence on immune maturation in infancy. OBJECTIVES: We aimed to explore the association between neonatal fecal flora and the development of atopic disorders until age 6 years, hypothesizing that the diversity of the intestinal microbiota influences disease development. METHODS: We studied the intestinal microbiota in infants in the Copenhagen Prospective Study on Asthma in Childhood, a clinical study of a birth cohort of 411 high-risk children followed for 6 years by clinical assessments at 6-month intervals, as well as at acute symptom exacerbations. Bacterial flora was analyzed at 1 and 12 months of age by using molecular techniques based on 16S rRNA PCR combined with denaturing gradient gel electrophoresis, as well as conventional culturing. The main outcome measures were the development of allergic sensitization (skin test and specific serum IgE), allergic rhinitis, peripheral blood eosinophil counts, asthma, and atopic dermatitis during the first 6 years of life. RESULTS: We found that bacterial diversity in the early intestinal flora 1 and 12 months after birth was inversely associated with the risk of allergic sensitization (serum specific IgE P = .003; skin prick test P = .017), peripheral blood eosinophils (P = .034), and allergic rhinitis (P = .007). There was no association with the development of asthma or atopic dermatitis. CONCLUSIONS: Reduced bacterial diversity of the infant's intestinal flora was associated with increased risk of allergic sensitization, allergic rhinitis, and peripheral blood eosinophilia, but not asthma or atopic dermatitis, in the first 6 years of life. These results support the general hypothesis that an imbalance in the intestinal microbiome is influencing the development of lifestyle-related disorders, such as allergic disease.

Elevated eosinophil protein X in urine from healthy neonates precedes development of atopy in the first 6 years of life.

RATIONALE: Biomarkers predicting development of atopic disease are needed for targeted preventive measures and to study if disease pathology may be active before onset of symptoms. OBJECTIVES: To investigate whether eosinophil protein X, leukotriene-C4/D4/E4, and 11ß-prostaglandin (PG) F2α (PGD2 metabolite) assessed in urine from healthy at-risk neonates precede development of atopic disease during the first 6 years of life. METHODS: We measured eosinophil protein X (n = 369), leukotriene-C4/D4/E4 (n = 367), and 11ß-PGF2α (n = 366) in urine from 1-month-old children participating in the Copenhagen Prospective Studies on Asthma in Childhood birth cohort. Clinical data on development of allergic sensitization, allergic rhinitis, nasal eosinophilia, blood eosinophilia, eczema, troublesome lung symptoms (significant cough or wheeze or dyspnea), and asthma were collected prospectively until age 6 years. Associations between urinary biomarkers and development of atopic traits were investigated using general estimating equations, logistic regression, and Cox regression. MEASUREMENTS AND MAIN RESULTS: Eosinophil protein X in the urine of the asymptomatic 1-month-old neonates was significantly associated with development of allergic sensitization (odds ratio, 1.49; 95% confidence interval [CI], 1.08­1.89), nasal eosinophilia (odds ratio, 3.2; 95% CI, 1.2­8.8), and eczema (hazard ratio, 1.4; 95% CI, 1.0­2.0), but not with allergic rhinitis, asthma, or blood eosinophilia. Neither leukotriene-C4/D4/E4 nor 11ß-PGF2α was associated with any of the atopic phenotypes. CONCLUSIONS: Eosinophil protein X in urine from asymptomatic neonates is a biomarker significantly associated with later development of allergic sensitization, nasal eosinophilia, and eczema during the first 6 years of life. These findings suggest activation of eosinophil granulocytes early in life before development of atopy-related symptoms.

Children with allergic and nonallergic rhinitis have a similar risk of asthma.

BACKGROUND: Both allergic and nonallergic rhinitis have been associated with increased prevalence of asthma. OBJECTIVE: To characterize asthma and intermediary asthma endpoints in young children with allergic and nonallergic rhinitis. METHODS: Thirty-eight 7-year-old children with allergic rhinitis, 67 with nonallergic rhinitis, and 185 without rhinitis from the Copenhagen Prospective Study on Asthma in Childhood birth cohort were compared for prevalence of asthma, eczema, food sensitization, filaggrin null-mutations, total IgE, blood eosinophil count, fractional exhaled nitric oxide (FeNO), lung function, and bronchial responsiveness. RESULTS: Children with allergic rhinitis compared with asymptomatic controls had increased prevalence of asthma (21% vs 5%; P = .002), food sensitization (47% vs 13%; P < .001), and eczema (66% vs 43%; P = .01) and increased total IgE (155 kU/L vs 41 kU/L; P < .001), blood eosinophil count (0.46 x 10(9)/L vs 0.30 x 10(9)/L; P = .01), FeNO (15.9 ppb vs 6.6 ppb; P < .001), and bronchial hyperresponsiveness (23% vs 9%; P = .008). Filaggrin null-mutations were associated with allergic rhinitis (odds ratio, 3.3; 95% CI, 1.3-8.3) but did not modify these associations. Children with nonallergic rhinitis also had increased asthma prevalence (20% vs 5%; P = .001) but showed no association with filaggrin null-mutations, eczema, food sensitization, total IgE, blood eosinophil count, FeNO, or bronchial responsiveness. CONCLUSION: Asthma is similarly associated with allergic and nonallergic rhinitis, suggesting a link between upper and lower airways beyond allergy associated inflammation. Only children with allergic rhinitis had increased bronchial responsiveness and elevated FeNO, suggesting different endotypes of asthma symptoms in young children with allergic and nonallergic rhinitis.

Upper and lower airway patency are associated in young children.

BACKGROUND: Although allergic rhinitis and asthma frequently coexist, the nature of this association is poorly understood. Therefore, we examined whether upper and lower airway patency are associated. METHODS: We investigated 221 6-year-old children from the Copenhagen Prospective Study on Asthma in Childhood birth cohort, assessing upper airway patency by acoustic rhinometry before and after alpha-agonist, and lower airway patency by spirometry before and after beta2-agonist. Furthermore, we measured blood eosinophil count, nasal eosinophilia, total IgE, and fraction of exhaled nitric oxide. Associations were investigated by generalized linear models. RESULTS: Decongested nasal airway patency and post-beta2 FEV(1) were significantly associated (P = .007). The association remained significant after adjustments for sex, body size, FVC, and atopic diseases (beta-coefficient 2.85 cm(3); 95% CI, 0.42 to 5.29; P = .02). Baseline values of upper and lower airway patency were also significantly associated (beta-coefficient 0.89 cm(3); 95% CI, 0.26-1.51; P = .01). In addition, blood eosinophil count and nasal eosinophilia were inversely associated with decongested nasal airway patency, beta-coefficient -0.42 cm(3) (95% CI, -0.77 to -0.07; P = .02) and beta-coefficient -0.47 cm(3) (95% CI, -0.89 to -0.05; P = .03), respectively. CONCLUSIONS: We found a strong and consistent association between upper and lower airway patency. This may be due to a common pathology, as suggested by the inverse association between decongested nasal airway patency, blood eosinophil count, and nasal eosinophilia. Alternatively, the association between upper and lower airway patency might reflect a physiologic background for the common comorbidity.