Immune maturation and modulation in childhood allergies : Aspects of epigenetic, mucosal and systemic immune mediators in allergy development and prevention

Abstract: The prevalence of allergic diseases has in the past century increased among children in affluent societies. Underlying causes are incompletely disentangled, but decreased diversity in environmental and microbial exposures could drive allergy development. Allergic individuals possess imbalanced immune responses, skewed in favour of Th2 cells along with lesser Th1 and Treg responses. As allergy development early in life increases the risk of developing further allergic manifestations later, early prevention is key. Thus, interventions in pregnancy, early life and childhood may modulate immunity towards tolerance, although underpinnings of immune maturation and modulation in allergy prevention throughout childhood are not entirely understood. In this thesis, these questions are addressed in children with a high propensity of developing allergic disease or who already have manifested allergies.Chemokines are crucial for immune cell recruitment to the allergic reaction site, and associate with allergy development in childhood. In Paper I, circulating levels of the allergy-related chemokines CCL17, CCL18, CCL22, CXCL10 and CXCL11 were studied in the natural course of allergic disease. Elevated levels of the Th2/Treg-regulated chemokine CCL18 in infancy and childhood associated with development of asthma and/or sensitisation. Moreover, this finding conferred higher odds of developing asthma and sensitisation from early school age until adolescence. Additionally, increased levels of the Th1-associated chemokines CXCL10 after birth, and decreased levels of CXCL11 at birth, preceded asthma development later in life. Hence, Paper I showed that circulating chemokine levels in different ways precede allergy development.Epigenetic modifications, such as DNA methylation, comprise a link between the genetic setup and environmental exposures, and regulate processes such as Th cell differentiation. Perinatal treatment with Lactobacillus reuteri and ω-3 fatty acids prevent development of some IgE-mediated manifestations. However, the drivers of the immunostimulating and pro-resolving effects of these treatments are sparsely examined. In Papers II and III, epigenome-wide DNA methylation patterns in CD4+ cells upon pre-and postnatal L. reuteri supplementation alone or in combination with ω-3 fatty acids were studied. In Paper II, the greatest epigenome wide differential methylation was evident at birth, mainly directed towards hypomethylation, indicating transcriptional availability of affected genes. Network analyses revealed several immune related pathways, and a relationship of differentially methylated genes to allergy development. Thus, prenatal L. reuteri treatment seemingly poises Th cells towards immune activation at birth, possibly influencing immune maturation as well as allergy development in the child.In Paper III, epigenome-wide DNA methylation patterns were surveyed at birth. In this on-going trial, mothers are treated during the latter half of pregnancy with a combination of L. reuteri and ω-3 fatty acids. Four different treatment groups were studied, and the largest differential methylation was seen in the double active treatment group. In contrast to Paper II, most CpGs and genes were hypermethylated, indicating repressed gene transcription. In line with Paper II, network analyses showed that T cell and immune mediated pathways were affected by treatment, and synergistic effects of the double treatment were indicated. Taken together, prenatal treatment with L. reuteri and/or ω-3 fatty acids altered the epigenome to different extents at birth, mainly towards hypermethylation, and often affected immune related pathways.Immunomodulatory effects of sublingual immunotherapy in children and adolescents are scarcely investigated. In Paper IV, circulating and salivary immune mediators were investigated in timothy grass-pollen allergic children treated with sublingual immunotherapy. Actively treated children had elevated levels of timothy grass pollen-specific IgA antibodies in saliva, along with increased circulating levels of the Th1-associated chemokines CXCL10 and CXCL11, both after treatment ending and two years later. Taken together, sublingual immunotherapy modulates local and peripheral immune responses in children with timothy grass pollen-induced allergy, by augmenting Th1-responses, lessening Th2-responses and inducing immunomodulatory responses, suggesting induction of tolerance, also partly in the long-term.Altogether, the studies in this thesis have shown altered immune regulation in children developing allergies. Moreover, immunomodulatory effects of prenatal treatment with probiotics and ω-3 fatty acids, and sublingual immunotherapy in children with grass pollen-induced allergic disease, were revealed. DNA methylation patterns and immunologic mediators in blood and saliva could potentially serve as appropriate biomarkers for allergic disease. Long term health benefits can be reached by intervening early in life, and further knowledge about the mechanisms behind this could promote the prevention of allergic diseases and hence improve the quality of life for children and adolescents.