A first step in primary disease prevention is identifying common, modifiable risk factors that contribute to a significant proportion of disease development. Infant respiratory viral infection and childhood asthma are the most common acute and chronic diseases of childhood, respectively. Common clinical features and links between these diseases have long been recognized, with early-life respiratory syncytial virus (RSV) and rhinovirus (RV) lower respiratory tract infections (LRTIs) being strongly associated with increased asthma risk. However, there has long been debate over the role of these respiratory viruses in asthma inception. In this article, we systematically review the evidence linking early-life RSV and RV LRTIs with asthma inception and whether they could therefore be targets for primary prevention efforts.

Background Women have an increased prevalence of severe asthma compared to men. IL-17A is associated with severe asthma and requires IL-23 receptor (IL-23R) signaling, which is negatively regulated by Let-7f miRNA. Objective Determine the mechanism by which 17β-estradiol (E2) and progesterone (P4) increase IL-17A production. Methods IL-17A production was determined by flow cytometry in Th17 cells from women (n=14) and men (n=15) with severe asthma. Cytokine levels were measured by ELISA and IL-23R and Let-7f expression by qPCR in Th17 differentiated cells from healthy women (n=13) and men (n=14). In sham-operated or ovariectomized female mice, 17β-E2, P4, 17β-E2+P4, or vehicle pellets were administered for 3 weeks prior to ex vivo Th17 cell differentiation. Airway neutrophil infiltration and KC expression was also determined in OVA-challenged WT female recipient mice with an adoptive transfer of OVA-specific Th17 cells from female and male mice. Results In severe asthma patients and healthy controls, IL-17A production was increased in Th17 cells from women compared to men. IL-23R expression was increased and Let-7f expression was decreased in Th17 differentiated cells from women compared to men. In ovariectomized mice, IL-17A and IL-23R expression was increased and Let-7f expression was decreased in the Th17 cells from mice administered 17β-E2+P4 compared to vehicle. Further, transfer of female OVA-specific Th17 cells increased acute neutrophil infiltration in the lungs of OVA-challenged recipient mice compared to transfer of male OVA-specific Th17 cells. Conclusions 17β-E2+P4 increased IL-17A production from Th17 cells, providing a potential mechanism for the increased prevalence of severe asthma in women compared to men.

BackgroundEnvironmental exposures that occur in utero and during early life may contribute to the development of childhood asthma through alteration of the human microbiome. The objectives of this study were to estimate the cumulative effect and relative importance of environmental exposures on the risk of childhood asthma.MethodsWe conducted a population-based birth cohort study of mother-child dyads who were born between 1995 and 2003 and were continuously enrolled in the PRIMA (Prevention of RSV: Impact on Morbidity and Asthma) cohort. The individual and cumulative impact of maternal urinary tract infections (UTI) during pregnancy, maternal colonization with group B streptococcus (GBS), mode of delivery, infant antibiotic use, and older siblings at home, on the risk of childhood asthma were estimated using logistic regression. Dose-response effect on childhood asthma risk was assessed for continuous risk factors: number of maternal UTIs during pregnancy, courses of infant antibiotics, and number of older siblings at home. We further assessed and compared the relative importance of these exposures on the asthma risk. In a subgroup of children for whom maternal antibiotic use during pregnancy information was available, the effect of maternal antibiotic use on the risk of childhood asthma was estimated.ResultsAmong 136,098 singleton birth infants, 13.29% developed asthma. In both univariate and adjusted analyses, maternal UTI during pregnancy (odds ratio [OR] 1.2, 95% confidence interval [CI] 1.18, 1.25; adjusted OR [AOR] 1.04, 95%CI 1.02, 1.07 for every additional UTI) and infant antibiotic use (OR 1.21, 95%CI 1.20, 1.22; AOR 1.16, 95%CI 1.15, 1.17 for every additional course) were associated with an increased risk of childhood asthma, while having older siblings at home (OR 0.92, 95%CI 0.91, 0.93; AOR 0.85, 95%CI 0.84, 0.87 for each additional sibling) was associated with a decreased risk of childhood asthma, in a dose-dependent manner. Compared with vaginal delivery, C-section delivery increased odds of childhood asthma by 34% (OR 1.34, 95%CI 1.29, 1.39) in the univariate analysis and 11% after adjusting for other environmental exposures and covariates (AOR 1.11, 95%CI 1.06, 1.15). Maternal GBS was associated with a significant increased risk of childhood asthma in the univariate analysis (OR 1.27, 95%CI 1.19, 1.35), but not in the adjusted analysis (AOR 1.03, 95%CI 0.96, 1.10). In the subgroup analysis of children whose maternal antibiotic use information was available, maternal antibiotic use was associated with an increased risk of childhood asthma in a similar dose-dependent manner in the univariate and adjusted analyses (OR 1.13, 95%CI 1.12, 1.15; AOR 1.06, 95%CI 1.05, 1.08 for every additional course). Compared with infants with the lowest number of exposures (no UTI during pregnancy, vaginal delivery, at least five older siblings at home, no antibiotics during infancy), infants with the highest number of exposures (at least three UTIs during pregnancy, C-section delivery, no older siblings, eight or mor...

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There is an error in the first sentence of the conclusion section of the abstract. The correct sentence is: Early-life exposures, maternal UTI during pregnancy (maternal antibiotic use), mode of delivery, infant antibiotic use, and having no older siblings at home, are associated with an increased risk of childhood asthma in a cumulative manner, and for those continuous variables, a dose-dependent relationship.