Prevention of allergy and asthma: interim report

The Role of Human Milk Immunomodulators in Protecting Against Viral Bronchiolitis and Development of Chronic Wheezing Illness

Infants who are breastfed are at an immunological advantage when compared with formula fed infants, evidenced by decreased incidence of infections and diminished propensity for long term conditions, including chronic wheeze and/or asthma. Exclusive breastfeeding reduces the duration of hospital admission, risk of respiratory failure and requirement for supplemental oxygen in infants hospitalised with bronchiolitis suggesting a potentially protective mechanism. This review examines the evidence and potential pathways for protection by immunomodulatory factors in human milk against the most common viral cause of bronchiolitis, respiratory syncytial virus (RSV), and subsequent recurrent wheeze in infants. Further investigations into the interplay between respiratory virus infections such as RSV and how they affect, and are affected by, human milk immunomodulators is necessary if we are to gain a true understanding of how breastfeeding protects many infants but not all against infections, and how this relates to long-term protection against conditions such as chronic wheezing illness or asthma.

Prognostic value of asymptomatic skin sensitization to aeroallergens

PURPOSE OF REVIEW

Asymptomatic skin sensitization to aeroallergens is frequently encountered in epidemiological studies and in everyday clinical life. Correct management of the condition is essential to avoid both progression into allergic disease and unnecessary intervention. Understanding immunological mechanisms in asymptomatic skin sensitization might provide new insights into the natural history and treatment of respiratory allergy.

RECENT FINDINGS

Research on asymptomatic skin sensitization is rare, and the present review unites previous studies with recent findings. It is a common condition affecting 8-30% of the population when using a local standard panel of aeroallergens. Clinically, immediate but not late-phase reactions are induced by allergen challenge. Absent eosinophil stimulation and migration and low IL-5 levels appear to be sentinel mechanisms. Prospective studies show that 30-60% become allergic, depending on allergens and follow-up period. No prospective intervention studies have been performed; however, allergen avoidance seems efficacious in reducing allergy development to occupational and domestic allergens. Asymptomatic skin sensitization due to an erroneously positive skin test must be ruled out before allergen avoidance measures are initiated.

SUMMARY

Surprisingly few papers exist on asymptomatic skin sensitization epidemiology and immunology, despite the intriguing question as to why symptoms do not develop in IgE-sensitized patients. It is a common condition and a risk factor for later development of respiratory allergic disease. Cross-sectional intervention studies suggest that allergy development is reduced by allergen avoidance. Immunologically, control of eosinophil stimulation and migration seems to be pivotal. How this control is maintained remains to be elucidated.

Can we prevent allergy?

Allergic conditions continue to increase steeply. The last two decades have seen many prevention trials, studying the effect of dietary and environmental interventions. These trials have yielded invaluable information about the atopic march and also highlighted the need for a clear and commonly used nomenclature as well as a need for better outcome measures. This review discusses primary and secondary prevention studies and their results.

[An increase in allergic diseases in childhood--current hypotheses and possible prevention]

During the last few decades there has ben a significant rise in the prevalence of allergic diseases such as asthma, hay fever and atopic dermatitis. Epidemiological studies strongly suggest that this increase is real and not due to changes in diagnostic labelling. It has become increasingly clear that a complex interplay between genetic and environmental factors account for this phenomenon. Genetically predisposed individuals are at an increased susceptibility to develop asthma or other allergic diseases when exposed to certain environmental or lifestyle factors. Particularly passive smoking has been shown to increase the risk for asthma in many studies and for atopy at least in some studies. This association is less clear for the exposure to sulfur dioxide, particulate matter, diesel exhaust and ozone. Lifestyle factors like socioeconomic status, sib-ship size, early childhood infections, dietary habits, growing up in antroposophic families or on a farm are more and more realised to be of great relevance for the development of allergic conditions. At the moment, there is a lot of uncertainty about which recommendations should be given for primary prevention. Recent studies have challenged the old paradigma that avoidance of early allergen contact could prevent the development of allergic disease. However, there is consensus that avoidance of smoking during pregnancy and avoidance of passive smoking during childhood should be recommended for primary prevention of asthma.

Tidal off-line exhaled nitric oxide measurements in a pre-school population

Exhaled nitric oxide (ENO) is used as a non-invasive marker of airway inflammation. The aim of this study was to measure ENO in a pre-school population using a relatively novel method, the off-line tidal breathing method, and to investigate differences in ENO between subjects with different presentations of wheezing. ENO was measured in 129 children (median age 4.4 years, quartiles 4.0-4.8 years) through a mouth mask attached to a two-way valve with an expiratory resistance of 5 cm H(2)0. Mean tidal ENO concentration (tENO) was calculated from triplicate measurements. Mean +/- SEM tENO for 89 control subjects was 13+/-0.4 ppb (95%CI 11.8-13.7 ppb); this level was significantly different from tENO in 15 children with a history of recurrent wheezing (18.6+/-1.9 ppb; 95%CI 14.5-22.7 ppb; t-test P<0.0001). Mean tENO in 16 children with a single wheezing episode was 11.4+/-1.0 ppb (95%CI 9.2-13.6 ppb) and thus significantly different from the recurrent wheezing group (t-test P=0.0024).

CONCLUSION

The off-line tidal breathing method is a feasible and appealing method for measuring exhaled nitric oxide in pre-school children. With this method, higher tidal exhaled nitric oxide levels were found in children with recurrent wheezing.

Pediatric allergy: a brief review of risk factors associated with developing allergic disease in childhood

OBJECTIVE

To briefly review some of the factors that have been implicated in the causation of the increased prevalence of allergic disease in children.

DATA SOURCES

MEDLINE search of original research and review articles related to the various risk factors considered responsible for the increased prevalence of allergic disease in children.

STUDY SELECTION

Author selected references.

CONCLUSIONS

It has been established that there is an increased prevalence of allergic disease, especially in children. Risk factors that are currently under investigation include: genetic atopic predisposition, early childhood allergen exposure and sensitization, occurrence of viral respiratory infections in young children, maternal smoking during pregnancy, poor dietary factors, lack of breast-feeding, childhood obesity, having a certain immunologic predisposition (Th2-prone), air pollution, and frequent immunizations in childhood. It is most likely that the occurrence of allergic disease will be found to be multifactorial.

Physiopathology of airway hyperresponsiveness

Airway hyperresponsiveness (AHR), the tendency of the airways to narrow too much and too easily in response to various stimuli, is a universal feature of asthma, although it is not exclusive to this disease. Airway responsiveness shows a unimodal distribution in the general population and might vary with time, increasing after exposure to allergens, industrial substances, or infectious agents in predisposed individuals, or decreasing for variable time periods after environmental or pharmacologic interventions. Airway inflammation and structural airway changes can lead to this heightened airway response, but the mechanisms by which they modify airway function are still unclear. They might be associated with increased contractile properties of the airways--from an increase in contractile elements, a change in smooth muscle mechanical properties, or a reduction of forces opposing bronchoconstriction, such as reduced airway-parenchymal interdependence. Other factors, such as neurohumoral influences and "geometric factors" (eg, airway caliber), can modulate the degree of AHR.

Atopic diseases of childhood

The atopic diseases of childhood consist of the triad of asthma, allergic rhinitis, and atopic dermatitis. All share a common pathogenesis, being mediated by IgE, and are frequently present together in the same individual and family. These disorders and their comorbidities comprise a large component of general pediatric practice and their incidence in developed countries has been increasing over the past few decades. They are a leading reason for clinic and emergency room visits, as well as hospital admissions. They have the potential to interfere with education, physical activity, socialization, and self-esteem. Fortunately, we now have a reasonable armamentarium of maintenance medications available to help control these disorders and improve the quality of life for children suffering from them. In addition, early diagnosis and aggressive management of these disorders seem to offer the possibility of altering their natural history. As such, developing a sensible approach to the diagnosis and treatment of these disorders in an outpatient setting is essential. In this review, I summarize the most current literature and provide a framework for effectively diagnosing and managing these disorders.