Microflora-associated characteristics in faeces from allergic and nonallergic infants

The role of the bacterial microbiome in lung disease

Novel culture-independent techniques have recently demonstrated that the lower respiratory tract, historically considered sterile in health, contains diverse communities of microbes: the lung microbiome. Increasing evidence supports the concept that a distinct microbiota of the lower respiratory tract is present both in health and in various respiratory diseases, although the biological and clinical significance of these findings remains undetermined. In this article, the authors review and synthesize published reports of the lung microbiota of healthy and diseased subjects, discuss trends of microbial diversity and constitution across disease states, and look to the extrapulmonary microbiome for hypotheses and future directions for study.

Probiotics, prebiotics and immunomodulation of gut mucosal defences: homeostasis and immunopathology

Probiotics are beneficial microbes that confer a realistic health benefit on the host, which in combination with prebiotics, (indigestible dietary fibre/carbohydrate), also confer a health benefit on the host via products resulting from anaerobic fermentation. There is a growing body of evidence documenting the immune-modulatory ability of probiotic bacteria, it is therefore reasonable to suggest that this is potentiated via a combination of prebiotics and probiotics as a symbiotic mix. The need for probiotic formulations has been appreciated for the health benefits in "topping up your good bacteria" or indeed in an attempt to normalise the dysbiotic microbiota associated with immunopathology. This review will focus on the immunomodulatory role of probiotics and prebiotics on the cells, molecules and immune responses in the gut mucosae, from epithelial barrier to priming of adaptive responses by antigen presenting cells: immune fate decision-tolerance or activation? Modulation of normal homeostatic mechanisms, coupled with findings from probiotic and prebiotic delivery in pathological studies, will highlight the role for these xenobiotics in dysbiosis associated with immunopathology in the context of inflammatory bowel disease, colorectal cancer and hypersensitivity.

Reduced gut microbial diversity in early life is associated with later development of eczema but not atopy in high-risk infants

BACKGROUND

Alterations in intestinal microflora have been linked to the development of allergic disease. Recent studies suggest that healthy infant immune development may depend on the establishment of a diverse gut microbiota rather than the presence or absence of specific microbial strains.

OBJECTIVES

We investigated the relationship between diversity of gut microbiota in the early postnatal period and subsequent development of eczema and atopy in the first year of life.

METHODS

Fecal samples were collected 1 wk after birth from 98 infants at high risk of allergic disease, who were followed prospectively to age 12 months. Fecal microbial diversity was assessed by terminal restriction fragment length polymorphism (T-RFLP) using restriction enzymes Sau96I and AluI, with a greater number of peaks representing greater diversity of bacterial communities.

RESULTS

Microbial diversity at day 7 was significantly lower in infants with eczema at age 12 months as compared to infants without eczema (AluI mean number of peaks 13.1 vs. 15.5, p = 0.003, 95% CI for difference in means -3.9, -0.8; Sau96I 14.7 vs. 17.2, p = 0.03, 95% CI -4.9, -0.3). No differences were observed for atopic compared to non-atopic infants, or infants with two allergic parents compared to those with one or no allergic parent.

CONCLUSIONS

A more diverse intestinal microbiota in the first week of life is associated with a reduced risk of subsequent eczema in infants at increased risk of allergic disease. Interventions that enhance microbial diversity in early life may provide an effective means for the prevention of eczema in high-risk infants.

Clinical Use of Probiotics in Pediatric Allergy (CUPPA): A World Allergy Organization Position Paper

BACKGROUND

: Probiotic administration has been proposed for the prevention and treatment of specific allergic manifestations such as eczema, rhinitis, gastrointestinal allergy, food allergy, and asthma. However, published statements and scientific opinions disagree about the clinical usefulness.

OBJECTIVE

: A World Allergy Organization Special Committee on Food Allergy and Nutrition review of the evidence regarding the use of probiotics for the prevention and treatment of allergy.

METHODS

: A qualitative and narrative review of the literature on probiotic treatment of allergic disease was carried out to address the diversity and variable quality of relevant studies. This variability precluded systematization, and an expert panel group discussion method was used to evaluate the literature. In the absence of systematic reviews of treatment, meta-analyses of prevention studies were used to provide data in support of probiotic applications.

RESULTS

: Despite the plethora of literature, probiotic research is still in its infancy. There is a need for basic microbiology research on the resident human microbiota. Mechanistic studies from biology, immunology, and genetics are needed before we can claim to harness the potential of immune modulatory effects of microbiota. Meanwhile, clinicians must take a step back and try to link disease state with alterations of the microbiota through well-controlled long-term studies to identify clinical indications.

CONCLUSIONS

: Probiotics do not have an established role in the prevention or treatment of allergy. No single probiotic supplement or class of supplements has been demonstrated to efficiently influence the course of any allergic manifestation or long-term disease or to be sufficient to do so. Further epidemiologic, immunologic, microbiologic, genetic, and clinical studies are necessary to determine whether probiotic supplements will be useful in preventing allergy. Until then, supplementation with probiotics remains empirical in allergy medicine. In the future, basic research should focus on homoeostatic studies, and clinical research should focus on preventive medicine applications, not only in allergy. Collaborations between allergo-immunologists and microbiologists in basic research and a multidisciplinary approach in clinical research are likely to be the most fruitful.

The microbiome of the lung

Investigation of the lung microbiome is a relatively new field. Although the lungs were classically believed to be sterile, recently published investigations have identified microbial communities in the lungs of healthy humans. At the present time, there are significant methodologic and technical hurdles that must be addressed in ongoing investigations, including distinguishing the microbiota of the upper and lower respiratory tracts. However, characterization of the lung microbiome is likely to provide important pathogenic insights into cystic fibrosis, respiratory disease of the newborn, chronic obstructive pulmonary disease, and asthma. In addition to characterization of the lung microbiome, the microbiota of the gastrointestinal tract have profound influence on the development and maintenance of lung immunity and inflammation. Further study of gastrointestinal-respiratory interactions is likely to yield important insights into the pathogenesis of pulmonary diseases, including asthma. As this field advances over the next several years, we anticipate that studies using larger cohorts, multicenter designs, and longitudinal sampling will add to our knowledge and understanding of the lung microbiome.

Microbial regulation of allergic responses to food

The incidence of food allergy in developed countries is rising at a rate that cannot be attributed to genetic variation alone. In this review, we discuss the environmental factors that may contribute to the increasing prevalence of potentially fatal anaphylactic responses to food. Decreased exposure to enteric infections due to advances in vaccination and sanitation, along with the adoption of high-fat (Western) diets, antibiotic use, Cesarean birth, and formula feeding of infants, have all been implicated in altering the enteric microbiome away from its ancestral state. This collection of resident commensal microbes performs many important physiological functions and plays a central role in the development of the immune system. We hypothesize that alterations in the microbiome interfere with immune system maturation, resulting in impairment of IgA production, reduced abundance of regulatory T cells, and Th2-skewing of baseline immune responses which drive aberrant responses to innocuous (food) antigens.

Composition of the early intestinal microbiota: knowledge, knowledge gaps and the use of high-throughput sequencing to address these gaps

The colonization, development and maturation of the newborn gastrointestinal tract that begins immediately at birth and continues for two years, is modulated by numerous factors including mode of delivery, feeding regime, maternal diet/weight, probiotic and prebiotic use and antibiotic exposure pre-, peri- and post-natally. While in the past, culture-based approaches were used to assess the impact of these factors on the gut microbiota, these have now largely been replaced by culture-independent DNA-based approaches and most recently, high-throughput sequencing-based forms thereof. The aim of this review is to summarize recent research into the modulatory factors that impact on the acquisition and development of the infant gut microbiota, to outline the knowledge recently gained through the use of culture-independent techniques and, in particular, highlight advances in high-throughput sequencing and how these technologies have, and will continue to, fill gaps in our knowledge with respect to the human intestinal microbiota.

Rhinoconjunctivitis prevalence and associated factors in school children aged 6-7 and 13-14 years old in Bogota, Colombia

OBJECTIVE

Allergic rhinitis is one of the most frequent chronic diseases among children. The objective of the study was to assess the prevalence of rhinoconjunctivitis and determine clinical, social and environmental associated factors, among school children aged 6-7 years and adolescents aged 13-14 years in Bogotá, Colombia.

METHODS

We used ISAAC (International Study of Asthma and Allergies in Childhood) phase III study methodology and questionnaire for design and data collection, and we did a secondary analysis of these data. The sample consisted of 3830 registers from adolescents between 13 and 14 years old and 3256 registers from children between 6 and 7 years.

RESULTS

The prevalence of rhinoconjunctivitis symptoms in the last year was 17.2% (95% CI, 15.9-18.5) in children vs. 24.9% (95% CI, 23.6-26.3) in adolescents. In both groups there was a female predominance in children (17.8% vs. 16.5%), and in the teenagers group (28.0% vs. 21.4%), though the differences were not statistically significant. The factors associated with rhinoconjunctivitis in the group of 6-7 years where: asthma [OR 3.9; (95% CI, 2.8-5.4)], atopic dermatitis [OR 2.3; (95% CI, 1.7-3.1)], use of acetaminophen in the last year [OR 2.6; (95% CI, 1.4-4.9)], use of antibiotics in the first year of live [OR 1.7; (95% CI, 1.3-2.3)], higher maternal education [OR 1.5; (95% CI, 1.0-2.3)] and cesarean delivery [OR 1.6; (95% CI, 1.2-2.1)]. Among the 13-14 year age-group, factors associated with rhinoconjunctivitis included: asthma [OR 2.6; (95% CI, 2.0-3.4)], atopic dermatitis [OR 1.8; (95% CI, 1.4-2.3)], use of acetaminophen in the last year [OR 1.8; (95% CI, 1.4-2.4)], consumption of fast-food three times or more per week [OR 1.5; (95% CI, 1.2-2.0), ever smoked [OR 1.4; (95% CI, 1.2-1.7)] and meat consumption was protective factor [OR 0.7; (95% CI, 0.5-0.9)].

CONCLUSION

In both studied groups, the estimated prevalence of rhinoconjunctivitis symptoms was relatively high. Future in-depth research is needed to assess the complex interactions between allergic rhinoconjunctivitis symptoms and social and environmental factors.

Regulatory T-cell abnormalities and the global epidemic of immuno-inflammatory disease

The incidence of autoimmune, allergic and inflammatory disease is increasing due to as yet unidentified environmental factors related to western living conditions. Here, I propose that alterations in the gut microbiome, acting via regulatory T cells (Tregs), may be responsible for this epidemic. Tregs control the threshold for peripheral antigen recognition via tonic downregulation of dendritic cell (DC) costimulation, and are also implicated in maintaining the tolerogenic function of DCs. In this model, minor perturbations in Treg number or function are predicted to lower the activation threshold, allowing proliferation and differentiation of self-reactive CD4T cells of too low an affinity to have undergone negative selection in the thymus. Failure to maintain the tolerogenic commitment of DCs exposed to commensal microbes and allergens could result in potentially pathogenic, allergic and inflammatory responses at epithelial surfaces.

The impact of perinatal immune development on mucosal homeostasis and chronic inflammation

The mucosal surfaces of the gut and airways have important barrier functions and regulate the induction of immunological tolerance. The rapidly increasing incidence of chronic inflammatory disorders of these surfaces, such as inflammatory bowel disease and asthma, indicates that the immune functions of these mucosae are becoming disrupted in humans. Recent data indicate that events in prenatal and neonatal life orchestrate mucosal homeostasis. Several environmental factors promote the perinatal programming of the immune system, including colonization of the gut and airways by commensal microorganisms. These complex microbial-host interactions operate in a delicate temporal and spatial manner and have an important role in the induction of homeostatic mechanisms.

Polydextrose enrichment of infant formula demonstrates prebiotic characteristics by altering intestinal microbiota, organic acid concentrations, and cytokine expression in suckling piglets

Oligosaccharides, the 3rd-most abundant component in human milk, are virtually absent from infant formulas and from the cow milk on which most are based. In breast-fed infants, human milk oligosaccharides (HMO) act as both receptor analogs, interfering with pathogen adhesion, and as prebiotics, stimulating the growth of certain commensal bacteria (e.g. bifidobacteria) and supporting the innate immunity. To further align the functional properties of infant formula with those of human milk, polydextrose (PDX) is proposed as a substitute for HMO. To determine the prebiotic functionality of PDX, 1-d-old pigs were fed a cow milk-based formula supplemented with increasing concentrations of PDX (0, 1.7, 4.3, 8.5, or 17 g/L) for 18 d (n = 13). Additional reference groups included pigs sampled at d 0 and sow-reared pigs sampled at d 18 (n = 12). Ileal Lactobacilli CFU, but not Bifidobacteria, increased linearly with increasing PDX (P = 0.02). The propionic acid concentration in digesta linearly increased with the PDX level (P = 0.045) and lactic acid increased linearly by 5-fold with increasing PDX (P = 0.001). Accordingly, digesta pH decreased linearly (P < 0.05) as PDX increased, with a maximal reduction approaching 0.5 pH units in pigs fed 17 g/L. Expression of TNFα, IL-1β, and IL-8 showed a negative quadratic pattern in response to PDX supplementation, declining at intermediate concentrations and rebounding at higher concentrations of PDX. In summary, PDX enrichment of infant formula resulted in a prebiotic effect by increasing ileal lactobacilli and propionic and lactic acid concentrations and decreasing pH with associated alterations in ileal cytokine expression.

Treatment and secondary prevention effects of the probiotics Lactobacillus paracasei or Bifidobacterium lactis on early infant eczema: randomized controlled trial with follow-up until age 3 years

BACKGROUND

Allergic disease has been associated with altered intestinal microbiota. Therefore, probiotics have been suggested as a potential treatment for eczema.

OBJECTIVE

We investigated whether dietary supplementation of infants with eczema at age 3-6 months with Lactobacillus paracasei CNCM I-2116 or Bifidobacterium lactis CNCM I-3446 had a treatment effect or altered allergic disease progression.

METHODS

Primary outcome included eczema severity (SCORing Atopic Dermatitis, SCORAD) 3 months post-randomization. Secondary: SCORAD (other visits); infant dermatitis quality of life (IDQoL); gastrointestinal permeability; urinary eosinophilic protein X; allergen-sensitization; allergic symptoms (age 12, 18, 36 months). A total of 208 infants aged 3-6 months with physician-diagnosed eczema were recruited; 137/208 (SCORAD ≥ 10, consuming ≥ 200 mL standard formula/day) were randomized to daily supplements containing L. paracasei or B. lactis or placebo for a 3-month period, while receiving extensively hydrolysed whey-formula (dairy-free diet). There were two open observational groups, one group exclusively breastfed (n = 22) and the other, standard formula-fed (n = 49).

TRIAL NUMBER

ISRCTN41490500.

RESULTS

Eczema severity decreased significantly over time in all groups. No significant difference was observed between randomized groups after 12-week treatment-period (SCORAD-score pre-/post-intervention: B. lactis 25.9 [95% CI: 22.8-29.2] to 12.8 [9.4-16.6]; L. paracasei 25.4 [22.1-29] to 12.5 [9.2-16.4]; placebo 26.9 [23.4-30.6] to 11.8 [9.6-14.3]; P = 0.7). Results were similar when analysis was controlled for allergen-sensitization, or when only sensitized infants were analysed. No differences were found for secondary outcomes. No difference was observed in SCORAD-score between randomized and observational groups.

CONCLUSION AND CLINICAL RELEVANCE

We found no benefit from supplementation with B. lactis or L. paracasei in the treatment of eczema, when given as an adjunct to basic topical treatment, and no effect on the progression of allergic disease from age 1 to 3 years.

Evaluation of stool microbiota signatures in two cohorts of Asian (Singapore and Indonesia) newborns at risk of atopy

Background

Studies have suggested that demographic and lifestyle factors could shape the composition of fecal microbiota in early life. This study evaluated infant stool microbiota signatures in two Asian populations, Singapore (n = 42) and Indonesia (n = 32) with contrasting socioeconomic development, and examined the putative influences of demographic factors on these human fecal associated bacterial signatures.

Results

Longitudinal analysis showed associations of geographical origin with Clostridium leptum, Atopobium and Bifidobacterium groups. Mode of delivery had the largest effect on stool microbiota signatures influencing the abundance of four bacterial groups. Significantly higher abundance of bacterial members belonging to the Bacteroides-Prevotella, Bifidobacterium and Atopobium groups, but lower abundance of Lactobacilli-Enterococci group members, were observed in vaginal delivered compared to caesarean delivered infants. Demographic factors influencing the structure of infants stool microbiota during the first year of life included breastfeeding, age of weaning, sibship size and exposure to antibiotics.

Conclusions

Differences in stool microbiota signatures were observed in relation to various demographic factors. These features may confound studies relating to the association of the structure of fecal microbiota and the predisposition to human modern disease.

Faecal microbiota and short-chain fatty acid levels in faeces from infants with cow's milk protein allergy

BACKGROUND

The present study was designed to compare the faecal microbiota and concentrations of faecal short-chain fatty acid and ammonia between healthy and cow's milk protein allergic (CMPA) infants.

METHODS

The population comprised 92 infants aged 2-12 months who were nonallergic (n = 46) or diagnosed as having CMPA (n = 46). Faecal samples were analyzed by fluorescent in situ hybridization and flow cytometry, using a panel of 10 rRNA targeted group- and species-specific oligonucleotide probes. Acetic, propionic, butyric, isocaproic and branched-chain short fatty acids (BCSFA) were measured by gas-liquid chromatography, lactate by enzymatic reaction, and pH and ammonia levels were determined.

RESULTS

CMPA infant faeces had significantly higher proportions of the Clostridium coccoides group and Atopobium cluster and a higher sum of the proportions of the different bacterial groups in comparison to healthy infant faeces. Faecal pH and ammonia did not significantly differ between CMPA and healthy infants. Faeces concentrations and percentages of butyric acid and BCSFA were higher in CMPA infants than in healthy infants.

CONCLUSIONS

The findings clearly set a link between a dysbiosis in gut microbiota composition and the pathogenesis of CMPA. No single species or genus appeared to play an essential role, but dysbiosis led to biomarkers of CMPA among bacterial fermentation products.

Dysregulation of allergic airway inflammation in the absence of microbial colonization

RATIONALE

The incidence of allergic disorders is increasing in developed countries and has been associated with reduced exposure to microbes and alterations in the commensal bacterial flora.

OBJECTIVES

To ascertain the relevance of commensal bacteria on the development of an allergic response, we used a model of allergic airway inflammation in germ-free (GF) mice that lack any exposure to pathogenic or nonpathogenic microorganisms.

METHODS

Allergic airway inflammation was induced in GF, specific pathogen-free (SPF), or recolonized mice by sensitization and challenge with ovalbumin. The resulting cellular infiltrate and cytokine production were measured.

MEASUREMENTS AND MAIN RESULTS

Our results show that the total number of infiltrating lymphocytes and eosinophils were elevated in the airways of allergic GF mice compared with control SPF mice, and that this increase could be reversed by recolonization of GF mice with the complex commensal flora of SPF mice. Exaggerated airway eosinophilia correlated with increased local production of Th2-associated cytokines, elevated IgE production, and an altered number and phenotype of conventional dendritic cells. Regulatory T-cell populations and regulatory cytokine levels were unaltered, but GF mice exhibited an increased number of basophils and decreased numbers of alveolar macrophages and plasmacytoid dendritic cells.

CONCLUSIONS

These data demonstrate that the presence of commensal bacteria is critical for ensuring normal cellular maturation, recruitment, and control of allergic airway inflammation.

Gut microbiota, probiotics, and vitamin D: interrelated exposures influencing allergy, asthma, and obesity?

Current evidence supports a role for gut colonization in promoting and maintaining a balanced immune response in early life. An altered or less diverse gut microbiota composition has been associated with atopic diseases, obesity, or both. Moreover, certain gut microbial strains have been shown to inhibit or attenuate immune responses associated with chronic inflammation in experimental models. However, there has been no fully adequate longitudinal study of the relation between the neonatal gut microbiota and the development of allergic diseases (eg, atopic asthma) and obesity. The emergence of promising experimental studies has led to several clinical trials of probiotics (live bacteria given orally that allow for intestinal colonization) in human subjects. Probiotic trials thus far have failed to show a consistent preventive or therapeutic effect on asthma or obesity. Previous trials of probiotics have been limited by small sample size, short duration of follow-up, or lack of state-of-the art analyses of the gut microbiota. Finally, there is emerging evidence that the vitamin D pathway might be important in gut homeostasis and in signaling between the microbiota and the host. Given the complexity of the gut micriobiota, additional research is needed before we can confidently establish whether its manipulation in early life can prevent or treat asthma, obesity, or both.

Germ-free status and altered caecal subdominant microbiota are associated with a high susceptibility to cow's milk allergy in mice

Studies suggesting that the development of atopy is linked to gut microbiota composition are inconclusive on whether dysbiosis precedes or arises from allergic symptoms. Using a mouse model of cow's milk allergy, we aimed at investigating the link between the intestinal microbiota, allergic sensitization, and the severity of symptoms. Germ-free and conventional mice were orally sensitized with whey proteins and cholera toxin, and then orally challenged with β-lactoglobulin (BLG). Allergic responses were monitored with clinical symptoms, plasma markers of sensitization, and the T-helper Th1/Th2/regulatory-T-cell balance. Microbiota compositions were analysed using denaturing gradient gel electrophoresis and culture methods. Germ-free mice were found to be more responsive than conventional mice to sensitization, displaying a greater reduction of rectal temperature upon challenge, higher levels of blood mouse mast cell protease-1 (mMCP-1) and BLG-specific immunoglobulin G1 (IgG1), and a systemic Th2-skewed response. This may be explained by a high susceptibility to release mMCP-1 even in the presence of low levels of IgE. Sensitization did not alter the microbiota composition. However, the absence of or low Staphylococcus colonization in the caecum was associated with high allergic manifestations. This work demonstrates that intestinal colonization protects against oral sensitization and allergic response. This is the first study to show a relationship between alterations within the subdominant microbiota and severity of food allergy.

Effect of mother's weight on infant's microbiota acquisition, composition, and activity during early infancy: a prospective follow-up study initiated in early pregnancy

BACKGROUND

It has been reported that deviations in gut microbiota composition may predispose toward obesity, and specific groups of commensal gut bacteria may harvest energy from food more efficiently than others. Alterations in microbiota compositions of mothers may be transferred to infants and lead to an increased risk of overweight.

OBJECTIVE

We analyzed the fecal microbiota composition of infants of overweight and normal-weight mothers and assessed the relations of weight and excessive weight gain of mothers during pregnancy on the microbiota of infants.

DESIGN

Mothers (n = 16) whose prepregnancy body mass index (BMI; in kg/m²) was ≥25 were selected with their infants from a prospective follow-up study of 256 women. Women with a BMI <25 (n = 26) and their infants served as control subjects. At the ages of 1 and 6 mo, infant stool samples were available for the analysis of microbiota composition by fluorescence in situ hybridization combined with flow cytometry and quantitative real-time polymerase chain reaction.

RESULTS

Infants' fecal microbial composition was related to the weight and weight gain of their mothers during pregnancy. Fecal Bacteroides and Staphylococcus concentrations were significantly higher in infants of overweight mothers during the first 6 mo. Higher weights and BMIs of mothers were related to higher concentrations of Bacteroides, Clostridium, and Staphylococcus and lower concentrations of the Bifidobacterium group. Prevalences of Akkermansia muciniphila, Staphylococcus, and Clostridium difficile groups were lower in infants of normal-weight mothers and of mothers with normal weight gains during pregnancy.

CONCLUSION

The composition and development of infant gut microbiota are influenced by BMI, weight, and weight gain of mothers during pregnancy.

Potential contribution of fungal infection and colonization to the development of allergy

Fungi have long been recognized as an important source of allergens in patients with atopic disease. In this review, we explore the hypothesis that fungal exposures resulting in colonization or infection directly influence the tendency of an individual to develop allergic disease. According to this hypothesis, fungal exposures especially those early in life may influence the manner in which the immune response handles subsequent responses to antigen exposures. Studies detailing this potential connection between fungi have already provided important insights into the immunology of fungal-human interactions and offer the potential to provide new approaches and targets for the therapy of allergic disease. The first half of this review summarizes the data concerning fungal infections and asthma, including possible connections between fungal infections and urban asthma. The second half explores the potential role of the fungal gastrointestinal microbiota in promoting allergic inflammation.

Silent mysteries: epigenetic paradigms could hold the key to conquering the epidemic of allergy and immune disease

Epigenetic mechanisms provide new insights into how environmental changes may mediate the increasing propensity for complex immune diseases such as allergic disease. There is now strong evidence that early environmental exposures play a key role in activating or silencing genes by altering DNA and histone methylation, histone acetylation and chromatin structure. These modifications determine the degree of DNA compaction and accessibility for gene transcription, altering gene expression, phenotype and disease susceptibility. While there is already evidence that a number of early environmental exposures are associated with an increased risk of allergic disease, several new studies indicate in utero microbial and dietary exposures can modify gene expression and allergic disease propensity through epigenetic modification. This review explores the evidence that immune development is under clear epigenetic regulation, including the pattern of T helper (Th)1 and Th2 cell differentiation, regulatory T cell differentiation, and more recently, Th17 development. It also considers the mechanisms of epigenetic regulation and early immune defects in allergy prone neonates. The inherent plasticity conferred by epigenetic mechanisms clearly also provides opportunities for environmental strategies that can re-programme gene expression for disease prevention. Identifying genes that are differentially silenced or activated in relation to subsequent disease will not only assist in identifying causal pathways, but may also help identify the contributing environmental factors.

A protective role for early oral exposures in the etiology of young adult Hodgkin lymphoma

The pattern of adolescent/young adult Hodgkin lymphoma (YAHL) suggests causation by a relatively late infection with a common childhood virus, but no causal virus has been found. Susceptibility is heritable and linked to lower interleukin 12 (IL12) levels, which can also result from fewer fecal-oral microbial exposures early in life. We studied twin pairs discordant for YAHL to examine exposures capable of altering the IL12 response and T-helper type 1 (Th1)-Th2 balance. One hundred eighty-eight YAHL-discordant twin pairs from the International Twin Study returned questionnaires (70% response). Exposure history of YAHL case-twins was compared with that of their unaffected control-twins using conditional logistic regression for matched pairs to calculate odds ratios (ORs). Behaviors likely to produce oral exposure to microbes conveyed decreases in risk (univariable OR range = 0.2-0.5, P = .003-.11). Significant adjusted ORs were seen for appendectomy (OR = 4.3, P = .001), eczema (OR = 4.2, P = .025), smoking (OR = 2.2, P = .054), and relatively more frequent behaviors associated with oral exposures (OR = 0.1; P = .004). Kappa statistics for intrapair agreement were higher than 0.8 for each significant finding. Our observations support a protective role for increased early oral exposure to the microbiome, suggesting that factors associated with increased Th2 and decreased Th1 cytokines are etiologically relevant to YAHL.

Immunomodulation by food: promising concept for mitigating allergic disease?

The importance of a properly functioning and well-balanced immune system for maintaining health has become strikingly evident over the past decades. Roughly since World War II, there has been an apparent decrease in the prevalence of "traditional" infectious diseases, with a concomitant increase in immune-related disorders, such as allergies. Causally, a relationship with changes in life-style-related factors such as the increasing use of hygienic practices seems likely. Diet and nutrition can affect the functioning of various immune parameters. This concept can be utilised in attempts to prevent or mitigate allergic reactions via the development of targeted food products or ingredients. This review describes recent findings with respect to food products and ingredients that show potential in this respect, with special emphasis on pro- and prebiotics, beta-glucans and fungal immunomodulatory proteins. What all of these approaches have in common is that they appear to strengthen Th1-mediated immunity, thus possibly restoring defective immune maturation due to overly hygienic living conditions: a little bit of dirt does not seem bad!

Faecal short chain fatty acid pattern and allergy in early childhood

AIM

To investigate whether functional changes of the gut flora over time were related to sensitization and allergic symptoms at four years of age.

METHODS

The levels of short chain fatty acids (SCFAs) in faecal samples at one (n = 139) and four (n = 53) years of age were related to the development of positive skin prick tests (SPT) and allergic symptoms during the first four years of life.

RESULTS

Faecal acetic (p < 0.01) and propionic (p < 0.01) acids decreased from one to four years of age, while valeric acid (p < 0.001) increased. Low levels of i-butyric (p = 0.01), i-valeric (p = 0.03) and valeric acids (p = 0.02) at one year were associated with questionnaire-reported symptoms of food allergy at four years. Positive SPTs and allergic symptoms at four years were associated with low faecal levels of i-butyric, i-valeric and valeric acids. At one year of age, infants with, as compared to without older siblings had higher median levels of valeric acid.

CONCLUSION

A slow functional maturation of the gut microflora, as measured by faecal levels of SCFAs is associated with allergy both at one and four years. The findings lend further support to an association between allergy and the development of microbial diversity.

The "Microflora Hypothesis" of allergic disease

Predisposition to allergic disease is a complex function of an individual's genetic background and, as is the case with multi-gene traits, environmental factors have important phenotypic consequences. Over a span of decades, a dramatic increase in the prevalence of allergic disease in westernized populations suggests the occurrence of critical changes in environmental pressures. Recently, it has been shown that the microbiota (i.e. microflora) of allergic individuals differs from that of non-allergic ones and that differences are detectable prior to the onset of atopy, consistent with a possible causative role. Features of the westernized lifestyle that are known to alter the microbiota, such as antibiotics and diet, are also associated with allergy in humans. In this chapter, we discuss the "Microflora Hypothesis" for allergy which predicts that an "unhealthy" microbiota composition, now commonly found within westernized communities, contributes to the development of allergy and conversely, that restoring a "healthy" microbiota, perhaps through probiotic supplementation, may prevent the development of allergy or even treat existing disease. In testing this hypothesis, our laboratory has recently reported that mice can develop allergic airway responses if their microbiota is altered at the time of first allergen exposure.

Birth by cesarean section, allergic rhinitis, and allergic sensitization among children with a parental history of atopy

BACKGROUND

Cesarean delivery can alter neonatal immune responses and increase the risk of atopy. Studies of the relation between cesarean delivery and allergic diseases in children not selected on the basis of a family history of atopy have yielded inconsistent findings.

OBJECTIVE

We sought to examine the relation between birth by cesarean delivery and atopy and allergic diseases in children at risk for atopy.

METHODS

We examined the relation between mode of delivery and the development of atopy and allergic diseases among 432 children with a parental history of atopy followed from birth to age 9 years. Asthma was defined as physician-diagnosed asthma and wheeze in the previous year, and allergic rhinitis was defined as physician-diagnosed allergic rhinitis and naso-ocular symptoms apart from colds in the previous year. Atopy was considered present at school age if there was 1 or more positive skin test response or specific IgE to common allergens. Stepwise logistic regression was used to study the relation between cesarean delivery and the outcomes of interest.

RESULTS

After adjustment for other covariates, children born by cesarean section had 2-fold higher odds of atopy than those born by vaginal delivery (odds ratio, 2.1; 95% CI, 1.1-3.9). In multivariate analyses birth by cesarean section was significantly associated with increased odds of allergic rhinitis (odds ratio, 1.8; 95% CI, 1.0-3.1) but not with asthma.

CONCLUSIONS

Our findings suggest that cesarean delivery is associated with allergic rhinitis and atopy among children with a parental history of asthma or allergies. This could be explained by lack of contact with the maternal vaginal/fecal flora or reduced/absent labor during cesarean delivery.

Asthma and obesity: common early-life influences in the inception of disease

The respective prevalences of both asthma and obesity have seen a significant rise in the past few decades. Although the association between these 2 conditions has been found in many studies from different areas around the world, the exact mechanisms for how this association arises remains unresolved. Because both asthma and obesity appear to have their beginnings in early childhood, common exposures that predispose individuals to both these conditions may explain how they are associated. These exposures include common genetic predictors, prenatal exposure to specific nutrients and overall maternal nutrition, patterns of colonization of the neonatal and infant gut, birth weight and infant weight gain, sedentary behaviors, and levels of adipokines in early life.

The genetic and environmental basis of atopic diseases

The prevalence of atopic diseases has increased abruptly in recent years in most Westernized societies, making the question why this happened the topic of a heated debate. The best paradigm available to date to explain this steep rise, the 'hygiene hypothesis', supports that it is the excess 'cleanliness' of our environments that has led to the decline in the number of infectious stimuli that are necessary for the proper development of our immune system. Recent findings support that it is the combined effect that not only pathogenic, but also non-pathogenic microorganisms, and even their structural components,can exert on the immune system that deters from the development of atopic responses. Adding to these results are intriguing new findings on the effect different gene polymorphisms can have on an individual's predisposition to allergic diseases. The most important linkages produced, to date, include those among the genes for IL-4, IL-13, HLA-DRB, TNF, LTA,FCER1B, IL-4RA, ADAM33, TCR alpha/delta, PHF11, GPRA, TIM, p40, CD14, DPP10, T-bet, GATA-3, and FOXP3 and allergic disorders. The two parallel research efforts, epidemiologic and genetic, are only recently starting to converge,producing fascinating results on the effect particular gene-environment interactions might have in the development of atopy.The most important lesson learned through this tremendous research effort is that not only a small number but thousands and millions of separate risk factors act in concordance in the production of the allergic phenotype.

Primary prevention of allergy: avoiding risk or providing protection?

Primary prevention strategies of allergy so far have been aimed to fight allergy causes, by avoiding risk factors and inhibiting their mechanisms of action. The results of trials testing food or airborne allergen avoidance as a prevention strategy were, however, rather disappointing. A reverse approach for primary prevention of allergies aims to facilitate exposure to protecting factors which promote the induction of immunologic tolerance against innocuous antigens. These factors are associated with farming environment and a 'traditional lifestyle', but identification of these factors is quite difficult. Major candidates include food-borne microbes, helminths or their components, which are able to stimulate mucosal immunity, particularly in the gut. Similarly, new preventive and therapeutic strategies are being tested to induce specific food-allergen oral tolerance through the ingestion of progressively increasing doses of the offending food. This shifting of allergy prevention research from avoidance to tolerance induction will hopefully allow us to reverse the epidemic trend of allergy diseases.

The role of the intestinal microbiota in the development of atopic disorders

The prevalence of atopic diseases, including eczema, allergic rhinoconjunctivitis and asthma, has increased worldwide, predominantly in westernized countries. Recent epidemiological studies and experimental research suggest that microbial stimulation of the immune system influences the development of tolerance to innocuous allergens. The gastrointestinal microbiota composition may be of particular interest, as it provides an early and major source of immune stimulation and seems to be a prerequisite for the development of oral tolerance. In this review the observational studies of the association between the gut microbiota and atopic diseases are discussed. Although most studies indicated an association between the gut microbiota composition and atopic sensitization or symptoms, no specific harmful or protective microbes can be identified yet. Some important methodological issues that have to be considered are the microbiological methods used (traditional culture vs molecular techniques), the timing of examining the gut microbiota, the definition of atopic outcomes, confounding and reverse causation. In conclusion, the microbiota hypothesis in atopic diseases is promising and deserves further attention. To gain more insight into the role of the gut microbiota in the etiology of atopy, large-scale prospective birth cohort studies using molecular methods to study the gut microbiota are needed.

Relationship between early intestinal colonization, mucosal immunoglobulin A production and systemic immune development

BACKGROUND

Variations in early intestinal colonization patterns have been implicated in the predispostion to allergic disease through effects on mucosal and systemic immune function.

METHODS

Colonization patterns and mucosal IgA production at 6 months of age were examined in relation to early exposures, systemic immune development and early allergic outcomes. This was performed in a cohort (n=189) who had received either Lactobacillus acidophilus or a placebo since birth.

RESULTS

Children who developed sensitization to one or more allergens by 12 months of age had significantly higher total (but not secretory) IgA levels at 6 months (P=0.024), but this was independent of probiotic treatment. There were no relationships between colonization patterns and IgA (total or secretory IgA) levels or allergic outcomes (sensitization, atopic dermatitis or food allergies). Breastfeeding, and the use of yoghurt or probiotic supplements were independently associated with significantly higher proportions of 'favourable' lactobacilli and bifidobacteria species. Caesarean delivery and the use of antibiotics during the first 6 months were not associated with significant variations in colonization. Higher proportions of 'favourable' bacteria (notably bifidobacteria) were associated with reduced production of most cytokine response to allergens, but increased expression of regulatory cell markers (P=0.009) and transforming growth factor-beta (P=0.016).

CONCLUSION

'Favourable' colonization, particularly with bifidobacteria, was associated with effects on cellular immune function, but this was not associated with mucosal immunity (secretory IgA) or reduced risk of allergic disease.

Lactobacillus Acidophilus strain L-92 regulates the production of Th1 cytokine as well as Th2 cytokines

BACKGROUND

There is growing interest in probiotics such as lactic acid bacteria (LAB), not only for treatment of T helper type (Th) 1-mediated diseases but also for Th2-mediated diseases, including allergic diseases, since lactic acid bacteria may be able to modulate the Th1/Th2 balance, in addition to having an immunomodulative effect through induction of Th1 bias.

METHODS

The effect of oral administration of heat-killed Lactobacillus acidophilus Strain L-92 (L-92) on ovalbumin (OVA)-specific immunoglobulin (Ig)E production was investigated in BALB/c mice. L-92 was orally administered to mice for 8 weeks from 2 weeks after initiation of OVA-immunization. Patterns of cytokine and Ig production in splenocytes and cells from Peyer's patches (PPs) from these mice were examined after restimulation with OVA in vitro.

RESULTS

L-92 significantly suppressed serum OVA-specific IgE levels for a long period. Cytokines such as interferon (IFN)-gamma, interleukin (IL)-4 and IL-10 and Igs such as total IgE and OVA-specific IgE were produced at significantly lower levels by splenocytes of L-92-treated mice, compared with those of control mice. In contrast, transforming growth factor (TGF)-beta and IgA levels produced by PPs from L-92-treated mice were significantly higher than in those from control mice.

CONCLUSIONS

Oral L-92 administration regulated both Th1 and Th2 cytokine responses, suppressed serum OVA-specific IgE, and induced TGF-beta production in PPs. TGF-beta is known to be associated with activation of regulatory T (Treg) cells. These data suggest that LAB may have immunomodulative effect by Treg cells via TGF-beta activity.

Using house dust extracts to understand the immunostimulatory activities of living environments

Laboratory and epidemiological studies have provided indirect but compelling evidence that toll-like receptor (TLR) signaling pathways play an important role in host responsiveness to ambient immunostimulatory factors. Nonetheless, direct evidence is limited. This paper will present our experience investigating the innate immunostimulatory activities of sterile house dust extracts (HDEs). In initial studies, bone marrow derived dendritic cells (BMDDCs) were cultured with HDEs, and cytokine production and co-stimulatory molecule expression were evaluated. In additional experiments, the TLR dependence of these responses was determined. HDEs induced concentration-dependent BMDDC activation. Moreover, the relative bioactivities of HDEs correlated with their endotoxin content. Finally, HDE-mediated responses were found to be partially dependent on TLR2, TLR4, and TLR9 and almost completely dependent on MyD88. These investigations provide the first direct evidence that TLR signaling pathways play a key role in innate responsiveness to non-infectious factors ubiquitous in living environments.

Importance of microbial colonization of the gut in early life to the development of immunity

The mammalian gastrointestinal tract harbors a complex microbiota consisting of between 500 and 1000 distinct microbial species. Comparative studies based on the germ-free gut have provided clear evidence that the gut microbiota is instrumental in promoting the development of both the gut and systemic immune systems. Early microbial exposure of the gut is thought to dramatically reduce the incidence of inflammatory, autoimmune and atopic diseases further fuelling the scientific viewpoint, that microbial colonization plays an important role in regulating and fine-tuning the immune system throughout life. Recent molecular diversity studies have provided additional evidence that the human gut microbiota is compositionally altered in individuals suffering from inflammatory bowel disorders, suggesting that specific bacterial species are important to maintaining immunological balance and health. New and exciting insights into how gut bacteria modulate the mammalian immune system are emerging. However, much remains to be elucidated about how commensal bacteria influence the function of cells of both the innate and adaptive immune systems in health and disease.

Increased risk of childhood asthma from antibiotic use in early life

BACKGROUND

To address the major methodological issues of reverse causation and selection bias in epidemiologic studies of antibiotic use in early life and the development of asthma, we undertook a cohort study of this association in a complete population of children.

METHODS

Using the health-care and prescription databases of Manitoba, Canada, this longitudinal study assessed the association between antibiotic prescription use during the first year of life and asthma at age 7 years in a 1995 birth cohort of 13,116 children.

RESULTS

Independent of well-known asthma risk factors, asthma was significantly more likely to develop in children who had received antibiotics in the first year of life at age 7 years. The association with asthma was observed for antibiotic use in non-respiratory tract infections (adjusted odds ratio [OR], 1.86; 95% confidence interval [CI], 1.02 to 3.37). The risk of asthma was highest in children receiving more than four courses of antibiotics (adjusted OR, 1.46; 95% CI, 1.14 to 1.88), especially among rural children, and in the absence of maternal asthma or a dog in the birth year. Broad-spectrum (BS) cephalosporin use was more common in these subpopulations of children.

CONCLUSIONS

Antibiotic use in early life was associated with the development of childhood asthma, a risk that may be reduced by avoiding the use of BS cephalosporins.

Neutral oligosaccharides in colostrum in relation to maternal allergy and allergy development in children up to 18 months of age

Several recent studies have demonstrated a relationship between the composition of the gut microbiota in infancy and subsequent development of allergic disease. Human milk is the major food in infancy and may thus profoundly influence the composition of the gut flora. Oligosaccharides in breast milk survive the passage through the stomach and are utilized by the gut microbiota. As the relationship between breast feeding and childhood allergy is controversial we hypothesized that the composition of oligosaccharides in breast milk might explain the controversy. Nine of the most abundant neutral oligosaccharides in human milk were analysed in colostrum samples from allergic and non-allergic women and related to subsequent development of allergy in their children. The carbohydrate fraction of the colostrum was separated by gel permeation chromatography and neutral oligosaccharides, tri- to hexasaccharides were collected. Neutral oligosaccharides were analysed with high-performance liquid chromatography. There was a large variation in the concentration of neutral oligosaccharides in colostrum, which could not be explained by the allergic status of the women. Allergic children consumed higher amounts of neutral oligosaccharides in total, although not significantly (p = 0.12). When different oligosaccharides were analysed separately, there was no significant difference in consumption between the infants who developed atopic allergy later (n = 9) and infants who did not (n = 11). Thus, the amount of neutral oligosaccharides in colostrum does not directly correlate with maternal allergy, nor with allergy development in children up to 18 months of age.

Probiotic supplementation for the first 6 months of life fails to reduce the risk of atopic dermatitis and increases the risk of allergen sensitization in high-risk children: a randomized controlled trial

BACKGROUND

Despite preliminary evidence, the role of probiotics in allergy prevention is unclear.

OBJECTIVE

To determine whether early probiotic supplementation prevents allergic disease in high-risk infants.

METHODS

Newborns of women with allergy (n = 231) received either Lactobacillus acidophilus (LAVRI-A1) or placebo daily for the first 6 months of life. Children were assessed for atopic dermatitis (AD) and other symptoms at 6 and 12 months and had allergen skin prick tests (SPT) at 12 months of age.

RESULTS

A total of 178 infants completed the supplementation period. Those in the probiotic group showed significantly higher rates of Lactobacillus colonization (P = .039). At 6 months, AD rates were similar in the probiotic (n = 23/89; 25.8%) and placebo (n = 20/88; 22.7%) groups (P = .629). There was also no difference at 12 months, although the proportion of children with SPT+AD was significantly higher in the probiotic group (P = .045). At 12 months, the rate of sensitization was significantly higher in the probiotic group (P = .030). The presence of culturable Lactobacilli or Bifidobacterium in stools in the first month of life was not associated with the risk of subsequent sensitization or disease; however, the presence of Lactobacillus at 6 months of age was associated with increased risk of subsequent cow's milk sensitization (P = .012).

CONCLUSION

Early probiotic supplementation with L acidophilus did not reduce the risk of AD in high-risk infants and was associated with increased allergen sensitization in infants receiving supplements. The long-term significance of the increased rate of sensitization needs to be investigated in further studies.

CLINICAL IMPLICATIONS

These findings challenge the role of probiotics in allergy prevention.

Evaluation of the effects of probiotic supplementation from the neonatal period on innate immune development in infancy

BACKGROUND

Activation of the innate immune system by microbial stimulation is believed to be critical for normal immune maturation, and there has been speculation that these pathways are important for inhibiting allergic-immune responses.

OBJECTIVE

To assess innate immune function following a 6-month supplementation with probiotic bacteria.

METHODS

Two hundred and thirty-one allergic, pregnant women were recruited into a randomized, controlled trial. The infants received either a probiotic (Lactobacillus acidophilus LAVRI-A1; Probiomics) or placebo (maltodextrin alone) daily for the first 6 months of life. Mononuclear cell samples were available from 118 infants. Functional responses to toll-like receptor (TLR) were assessed using ligands for TLR2 (Pansorbin) and TLR4/CD14 [lipopolysaccharide (LPS)] and measuring cytokine responses in the supernatants. Antigen-presenting cell function, as well as capacity for cytokine production (IL-12p70 and IL-10) was assessed.

RESULTS

Infants in the probiotic group did not demonstrate differences in innate immune function compared with those in the control group. No differences were seen when cytokine responses were examined following stimulation with Pansorbin (TLR2) or LPS (TLR4). Similarly, no differences were seen in the antigen-presenting capacity of these infants. The mean fluorescence intensities of human leucocyte antigen-DR (HLA-DR) on monocytes, B cells and dendritic cells (DC) subsets were not affected, nor were the percentage of circulating DC subsets affected by a 6-month supplementation with L. acidophilus LAVRI-A1.

CONCLUSIONS

Probiotic supplementation with L. acidophilus for the first 6 months of life did not alter early innate immune responses in this population at high risk of developing allergic disease.

Effects of probiotic supplementation for the first 6 months of life on allergen- and vaccine-specific immune responses

BACKGROUND

A reduction in microbial burden during infancy when allergen-specific memory is evolving has become a prominent explanation for the allergy epidemic.

OBJECTIVE

We sought to determine whether probiotic dietary supplementation in the first 6 months of life could modify allergen- and vaccine-specific immune responses.

METHODS

Two hundred and thirty-one pregnant women with a history of allergic disease and positive allergen skin prick test (SPT) were recruited into a randomized-controlled trial. The infants received either a probiotic (3 x 10(9)Lactobacillus acidophilus LAVRI-A1; Probiomics) or placebo (maltodextrin alone) daily for the first 6 months of life, given independent of feeding methods. One hundred and seventy-eight children completed the study; blood samples were available from 60 children in the placebo group and 58 children in the probiotic group. Infant cytokine (IL-5, IL-6, IL-10, IL-13, TNF-alpha or TGF-beta) responses to tetanus toxoid (TT), house dust mite (HDM), ovalbumin (OVA), beta-lactoglobulin (BLG), Staphylococcus enterotoxin B (SEB) and phytohaemaglutinin (PHA) were measured at 6 months of age.

RESULTS

Children who received the probiotics showed reduced production of IL-5 and TGF-beta in response to polyclonal (SEB) stimulation (P=0.044 and 0.015, respectively). They also demonstrated significantly lower IL-10 responses to TT vaccine antigen compared with the placebo group (P=0.03), and this was not due to any differences in vaccination. However, there were no significant effects of probiotics on either Type 1 (Th1) or Type 2 (Th2) T helper cell responses to allergens or other stimuli. The only other effects observed were for reduced TNF-alpha and IL-10 responsiveness to HDM allergens in children receiving probiotics (P=0.046 and 0.014, respectively).

CONCLUSIONS

In summary, although we did not see any consistent effects on allergen-specific responses, our study suggests that probiotics may have immunomodulatory effects on vaccine responses. The significance and clinical relevance of this need to be determined in further studies.

Fecal microbiota in sensitized wheezy and non-sensitized non-wheezy children: a nested case-control study

BACKGROUND

It has been suggested that intestinal microbiota of allergic and non-allergic children differs in composition, and that microbiota-immune system interactions may predispose children to develop sensitization. Previous studies have examined fecal microbiota of allergic children with atopic dermatitis, but little is known about that of atopic wheezy children.

OBJECTIVE

To investigate the composition of the fecal microbiota of young sensitized wheezy and non-sensitized non-wheezy children, using molecular methods.

METHODS

Within the context of a prospective birth cohort, we carried out a nested case-control study of sensitized wheezy children (cases) and non-sensitized non-wheezy controls. Cases and controls were matched for age, sex, parental atopy, allergen exposure, and pet ownership. We evaluated the composition of fecal microbiota by nucleic acid-based methods (PCR combined with denaturing gradient gel electrophoresis and quantification of bifidobacteria by fluorescent in situ hybridization).

RESULTS

Thirty-three case-control pairs (mean age 4.4 years) provided stool samples. Comparison of total bacterial community profiles showed that each child had a unique fecal microbiota (mean Dice's similarity coefficient 22%, range 3.3-60.8%). There was no difference between the groups in prevalence of Lactic Acid bacteria (12/33 vs. 11/33, P=0.8) or bifidobacteria (30/33 vs. 31/33, P=1.00, cases vs. controls). The bifidobacterial species detected were similar in both groups. The percentage of bifidobacteria in total fecal microflora was no different between cases (median 1.7%, range 0-20.8%) and controls (1.9%, 0-18.2%, P=0.7). However, cases with eczema had significantly fewer bifidobacteria (median 1.6%, range 0-4.8%) than their controls (4.0%, 1.9-18.2%, P=0.05).

CONCLUSION

We found no differences in fecal microbiota composition between sensitized wheezy and non-sensitized, non-wheezy children aged 3-5 years using nucleic acid-based methods. Differences appear to be isolated to those allergic children with eczema.

Genetics of food allergy

Allergic reactions to foods are an important medical problem throughout the industrialized world. The occurrence of food allergy appears to be strongly influenced by genetics, but the basis of the genetic predisposition to food allergy has not been differentiated from that for atopy in general. In addition, genetic susceptibility alone does not explain the prevalence of food allergy satisfactorily, leaving ample room to consider the importance of environmental influences (external, maternal, and gastrointestinal environment) and interactions between the host and the environment. Several features of food allergy are highlighted in this review: 1) patients with severe food allergies are overwhelmingly atopic, but food allergy occurs only in approximately 10% of patients with other atopic diseases; 2) most patients are clinically reactive to a single food, and although a substantial minority have multiple food allergies, the variety of bone fide food allergies in a given individual is limited; 3) foods contain multiple proteins whereas only a small subset are allergenic; 4) there is likely an important contribution of the environment, becoming manifest in genetically susceptible individuals.

Toll-like receptor ligands and atopy: a coin with at least two sides

Allergic disease prevalence rates have increased dramatically in affluent countries over the last half century. One proposed explanation is that decreased exposures to microbes caused by modern public health practices has led to deficiencies in an important source of immune education and a consequent increase in the risk of pathogenic immune responses to environmental antigens. Recently, it has become clear that innate responses to microbes are mediated in large part by Toll-like receptors (TLRs), which recognize a diverse family of ligands produced by viruses, bacteria, and fungi. In this perspectives article we will review experimental evidence suggesting that TLRs also play a dominant role in innate responses to noninfectious immunostimulatory materials present in environments of daily living. We will further discuss how ligands for different TLRs can polarize the T(H) bias of adaptive responses in opposing directions. Finally, we will consider how TLRs might contribute to the genesis of atopy and the clinical potential of pharmacologic interventions that target TLRs for the prevention and treatment of allergic diseases.

Distinct Pattern of Commensal Gut Microbiota in Toddlers with Eczema

BACKGROUND

Recent studies have demonstrated differences in the composition of gut microbiota in infants with and without allergic diseases, particularly eczema.

METHODS

A case-control study involving 21 toddlers (age 3.0 +/- 0.5 years) with and 28 age-matched toddlers without eczema was conducted. Four groups of aerobic gut microbiota were identified and quantitated in stool samples grown on selective media. Three groups of anaerobes were enumerated by fluorescent in situ hybridization followed by quantitative flow cytometry. We also performed molecular typing of lactic-acid-producing bacteria (LAB) and enterococcal isolates to facilitate detailed analysis at species level by bacterial 16S rDNA sequencing.

RESULTS

Toddlers with eczema harbored significantly lower counts of Bifidobacterium [(median 0.14 (25th and 75th percentile: 0.04 and 0.47) vs. 0.71% (0.16, 1.79) of cells acquired, p = 0.003)] and Clostridium [(0.28 (0.09, 0.78) vs. 0.83% (0.35, 1.82) of cells acquired, p = 0.012)] but significantly higher counts of total LAB [7.3 (6.1, 8.5) vs. 5.7 (4.4, 7.3) log CFU/g, p = 0.006] in particular enterococci [6.3 (4.8, 7.4) vs. 5.0 (3.4, 6.4) log CFU/g, p = 0.018]. There was no significant correlation between eczema severity score and bifidobacterial counts.

CONCLUSION

The results further confirm previous reports that the gut microecosystem differs between children with and without eczema and extend them beyond infancy.