Development of sensitization versus tolerance to inhalant allergens during early life

Can we prevent food allergy by manipulating the timing of food exposure?

Prevention of food allergies by maternal and infant feeding practices serves as a simple, inexpensive approach to address the growing number of subjects with food allergies in comparison with any emerging interventional therapies for existing food allergies, such as oral immunotherapy. This article provides a careful evaluation of the rationale and existing data on the effect of timing of the introduction of food allergens (during pregnancy, lactation, and early childhood) on the development of specific food allergies.

Atopic dermatitis in young children is associated with impaired interleukin-10 and interferon-gamma responses to allergens, vaccines and colonizing skin and gut bacteria

BACKGROUND

A significant proportion of children with food allergy and more severe forms of atopic dermatis (AD) go on to develop persistent forms of allergic disease such asthma. Defining immune dysregulation in these children will be of great value in understanding disease pathogenesis.

OBJECTIVE

In this study we characterized the immune responses of young infants (6-18 months of age) with moderate-to-severe AD (a modified SCORAD>or=25) and compared these (n=53) with responses of non-allergic children with no history of dermatitis or sensitization of the same age (n=20).

METHODS

Mononuclear cell cytokine responses to allergens (egg ovalbumin (OVA), beta-lactoglobulin (BLG), house dust mite (HDM)), vaccines (tetanus toxoid (TT), diphtheria toxoid (DT)), intestinal flora (heat-killed Lactobacillus species (HKLB)), heat-killed Staphylococcus aureus (HKSA), S. aureus enterotoxin B (SEB) and mitogen (phytohaemaglutinin (PHA)) were compared in children with AD with unaffected children.

RESULTS

Children with AD had significantly lower spontaneous (unstimulated) production of regulatory cytokine IL-10 (P<0.001), as well as IFN-gamma (P<0.001) and TNF-alpha (P<0.001) compared with the unaffected children. After allowing for differences in baseline levels IL-10 responses to virtually all stimuli (food allergens (P=0.003), vaccines P=0.01, intestinal flora (heat-killed Lactobacillus species (HKLB), P=0.005) and skin flora (heat-killed Staphylococcus aureus (HKSA), P=0.003)) were also significantly attenuated in children with AD. The only exception was HDM, to which responses were stronger in children with AD [P=0.05]. Although there were no significant correlations between HDM IgE and HDM cytokine responses at this age, T-helper type 2 (Th2) IL-5 (P=0.014) and IL-13 (P=0.004) responses to HDM were significantly more frequent in the children with AD. However, while children with AD showed significantly attenuated Th1 IFN-gamma responses to food allergens (OVA, P=0.007 and BLG, P<0.001) and vaccines (DT, P=0.008 and TT, P<0.001), these children showed no difference in Th1 IFN-gamma responses to HDM or microbial agents (HKSA and HKLB).

CONCLUSION

A increase in propensity for Th2 responses to aeroallergens in children with AD is associated with early impaired production of IL-10 regulatory cytokine to a broad range of environmental stimuli including foods, intestinal flora, S. aureus, and vaccines.

Decreased nasal tolerance to allergic asthma in mice fed an amino acid-based protein-free diet

Intranasal (i.n.) administration of soluble proteins induces a state of specific unresponsiveness to subsequent immunization, known as nasal tolerance. It is thought that newborns are less susceptible to nasal tolerance induction. Recently, we have shown that feeding adult animals with a protein-free diet (Aa) resulted in their arrest at an immature immunological profile. Here, we examined the effects of the Aa diet on the development of nasal tolerance to ovalbumin (OVA) in a murine model of allergic asthma. Nasal OVA administration suppressed almost totally the OVA-induced asthma-like responses (airway eosinophilia, type 2 cytokine production, and OVA-specific IgE antibodies) in chow- or casein-fed BALB/c mice. In contrast, in Aa-fed animals the suppression of asthma-like responses by nasal OVA was partial, being effective in suppressing airway eosinophilia, but not airway type 2 cytokine or OVA-specific IgE response. We conclude that animals fed the Aa diet are more resistant to the induction of nasal tolerance. Our animal model may mimic the features of the immune system of human infants.

Dietary prevention of allergic diseases in infants and small children. Part I: immunologic background and criteria for hypoallergenicity

The role of primary prevention of allergic diseases has been a matter of debate for the last 40 years. In order to shed some light into this issue, a group of experts of the Section of Pediatrics EAACI critically reviewed the existing literature on the subject. In this paper, the immunology of the fetus and newborn is reviewed as well as the post-natal development of the immune system. The influence of post-natal environment and breastfeeding on tolerance induction and sensitization are examined. Allergic diseases result from a strong relationship between genetic and environmental factors. Sensitization to food allergens occurs in the first year of life and cow's milk allergy is the first food allergy to appear in the susceptible infants. Hypoallergenicity of food formulas to be used is a critical issue both for treatment of cow's milk-allergic children and for prevention. Methods to document hypoallergenicity are discussed and evaluated in the preclinical and clinical steps.

Neonatal interleukin-12 capacity is associated with variations in allergen-specific immune responses in the neonatal and postnatal periods

BACKGROUND AND OBJECTIVES

A reduced capacity of antigen presenting cells (APC) to provide pro-T helper 1 (Th1) signals, such as IL-12, to T cells during early life may be implicated in the development of T helper 2 (Th2)-mediated allergic disease. In this study we examined the relationships between the capacity for IL-12 responses in the neonatal period and atopic risk (family allergy), in vitro T cell responses to allergens, and the subsequent development of allergic disease at 6 years.

METHODS

The capacity of circulating neonatal (and maternal) APC to produce IL-12 p70 in response to LPS (and IFN-gamma) stimulation was assessed in a group of 60 children with previously well-characterized immune responses to allergens and atopic outcomes. The IL-12 responses were compared with allergen-induced lymphoproliferation (to house dust mite (HDM) ovalbumin (OVA), cat and beta-lactoglobulin (BLG)) and IL-13 and IFN-gamma cytokine responses (to OVA, HDM and phytohaemaglutinin (PHA)) in the neonatal and postnatal periods. IL-12 responses were also compared according to atopic risk and atopic outcomes (doctor-diagnosed asthma, eczema, food allergies and sensitization as evidenced by skin prick testing) at 6 years clinical follow-up.

RESULTS

Maternal peripheral blood mononuclear cells (PBMC) synthesized significantly greater amounts of IL-12 than neonatal PBMC, though within maternal-infant pairs IL-12 responses were significantly correlated (r = 0.4, P = 0.019). Moreover, neonatal IL-12 responses were positively correlated with neonatal allergen proliferation for HDM (r = 0.6, P < 0.0001), OVA (r = 0.55, P < 0.0001), cat (r = 0.5, P = 0.003) and BLG (r = 0.55, P = 0.001), but negatively correlated with neonatal IL-13 responses to both allergens tested (HDM: r = - 0.4, P = 0.03 and OVA: r = - 0.5, P = 0.001). Both neonatal and maternal IL-12 responses were positively correlated with postnatal IFN-gamma responses to HDM at 12, 18 and 24 months of age (responses after age of 2 years were not assessed). There was no relationship between atopic risk and IL-12 capacity in the neonatal period, but there was a (non-significant) trend for neonatal IL-12 responses to be lower in the high-risk children who developed clinical allergy at 6 years (compared with the low risk group) although the number in this analysis was small.

CONCLUSIONS

Reduced APC IL-12 production in the perinatal period was associated with reduced T cell activation (lymphoproliferation), stronger neonatal Th2 responses, and weaker Th1 responses to allergen in the postnatal period. This supports the notion that variations in APC function in early life may contribute to altered allergen-specific cytokine responses associated with later allergy.

Novel probiotics for the management of allergic inflammation

Several pathologies of the gastrointestinal tract, particularly food allergy, are due to an exaggerated and imbalanced response of the gut mucosal immune system. The intestinal microflora is an important constituent of the gut mucosal barrier against food allergens and there is increasing evidence that one important acquired factor predisposing to food allergy in infants is the gut microflora. Indeed, the balance of bifidobacteria versus Clostridia in the neonatal flora appears to determine the allergic status in infants. In earlier studies, it was shown that the higher prevalence of allergies in infants fed standard formulas, compared to breast-fed infants, correlated with lower frequencies of bifidobacteria in their faeces. Certain Lactobacillus probiotic strains can have an inhibitory impact on allergic inflammation. The mechanisms implicated are still unclear, but it seems that they can involve both proteolytic and/or immunomodulatory functions. One challenge will be to find a probiotic strain that elicits all these functions and that fulfills all safety criteria.

Suppression of autologous peripheral blood mononuclear cell proliferation by alveolar macrophages from young infants

Maintenance of lung homeostasis involves a complex interaction between T lymphocytes and alveolar macrophages (AM), in which AM suppress pulmonary T cell proliferation to antigenic stimuli. To assess whether AM-mediated suppression is attenuated in healthy young infants, AM and peripheral blood mononuclear cells (PBMC) were sampled prior to elective surgery. Children were divided into <4 months of age (Group I) and >4 months (Group II). Autologous PBMC and AM were co-cultured in vitro with phytohaemaglutinin (PHA) at AM : PBMC ratios ranging from 2:1 to 1 : 5. Methyl-tritiated thymidine was added after 48 h and uptake determined at 72 h. Percentage suppression or enhancement of PBMC proliferation by AM was determined relative to proliferation of PBMC with PHA. To determine the role of soluble factors of suppression, cell-free supernatants from paediatric AM and PBMC co-cultures were added to PHA-stimulated adult PBMC. The median age was 3 months for Group I (n = 9) and 7 years 2 months (n = 13) for Group II. Percentage suppression of PBMC proliferation was attenuated in Group I (versus Group II) at AM : PBMC ratios of 2:1 (median 78 versus 92, P< 0 x 05) and 1 : 1 (45 versus 87, P< 0 x 01). Cell-free supernatants from Groups I and II suppressed proliferation of adult PBMC, but there was no difference in suppression between the age groups. We conclude that suppression of autologous PHA-stimulated PBMC proliferation by AM is attenuated in young infants, and this immaturity is not explained by reduced release of soluble factors.

Early life factors related to clinical manifestations of atopic disease but not to skin-prick test positivity in young children

The relative influence of early life events in the development of IgE-mediated allergy is still undetermined. We investigated early life factors in relation to skin-prick test positivity (SPT) and clinical manifestations of atopic disease in a population-based sample of 201 Italian children (3 months-5 years), after considering their interactions with known determinants of allergy. Among them, 143 children had SPT performed to common allergens. Threatened abortions, general anesthesia at delivery, prematurity, birthweight < 2500 g, maternal smoking, dampness and gas heating exposure were all significantly related to an increased risk of frequent rhinitis in the absence of cold (18%). In utero smoking, threatened abortions, fetal health complications, infantile colic, maternal smoking in childhood (satisfactorily correlated with maternal expired CO during the survey) and respiratory infections were all independent determinants of frequent wheezing (23%). Doctor's diagnosis of asthma (3%) was related to in utero smoking, being born in spring, infantile colic and respiratory infections. A simultaneous exposure to in utero smoking and infantile colic put the infants to a fourfold higher risk of frequent wheezing and to a ninefold risk of asthma, respectively. Having a pet and washing blankets at < 60 degrees C were inversely related to frequent wheezing. Data confirmed also that maternal phenotype influences the inheritance of atopic disease. No event, except a low intake of fruit (< 3/week), was significantly associated with positive SPT (20%) or eczema. Besides allergic sensitization, other events, which occur early in life, seem critical to the development of IgE-mediated allergy.

Allergic disease in teenagers in relation to urban or rural residence at various stages of childhood

BACKGROUND

Higher prevalences of allergic diseases and IgE antibodies to inhalant allergens have been reported for persons living in urban areas than for persons living in rural areas.

METHODS

Associations between cumulative incidences of allergic diseases in 1878 children aged 13-14 years and their place of residence (urban, semiurban, or rural) from birth were assessed by questionnaire (ISAAC), in order to find out whether there is a period of increased sensitivity to external influences during the first few years of life. Family history and exposure to pets, tobacco smoke, and damp were considered in multiple regression.

RESULTS

There was a significantly higher prevalence of allergic diseases with urban residence than with rural residence during the first 2 years of life (e.g., for bronchial asthma, relative risk (RR) for the first year 2.1, 95% CI 1.2-3.7). An increased risk was still found after multiple regression (RR=1.7). Semiurban residence was associated with an intermediate cumulative incidence of allergic diseases. Maternal smoking during pregnancy was associated with asthma (RR=1.4, 95% CI 1.0-2.0).

CONCLUSIONS

The findings support a period of increased susceptibility during the first years of life. Whether rural lifestyle protects against allergy or whether urban pollutants contribute to allergy has to be elucidated [corrected].