Cockroach Allergens May Play Key Role in the Development of the Asthma Epidemic.
Mucosal exposure to allergens leads to development of allergic sensitization. This may cause the development of asthma, which is characterized by chronic airway inflammation. Researchers studied the allergic effect of cockroach extracts in mice. It was found that exposure of mucosa (mucus secreting inner linings) to cockroach extract induces allergic reactions even in the absence of adjuvants.
More than 30% of the world’s population suffers atopy and allergic diseases. A study in 10 European countries showed that respiratory allergic conditions alone have a prevalence of up to 36.6%. These diseases pose severe global economic burden. In spite of all the efforts that spanned over the past three decades, the underlying mechanisms of allergic reactions have not been completely understood.
Cockroach allergens are an important cause of asthma exacerbations in many parts of the world. Early life exposure to cockroach allergens is supposed to lead to the development of specific allergic sensitization to cockroaches. The risk for persistent asthma and bronchial hyperresponsiveness is increased by childhood exposure. Cockroach-derived proteins that we inhale arise from several sources, including cockroach saliva, feces, cast skins, debris and dead bodies.
Most of the studies have been done in animal models. Animal models have aided profoundly in learning about the pathogenesis of allergic conditions, especially asthma. Animal models of asthma have a number of limitations. Humans and animals may differ in the development of allergic immune responses. An allergen may not evoke the same allergic reaction in animals as in humans. The utility of murine models of asthma as predictors of the response of human asthma to therapeutics has been a subject of controversy. Hence multiple models are required for better understandings.
A number of different models in mice have been developed for the purpose. Recent studies of allergic responses to cockroach extracts were performed in mice. The mucosa lining the nasal cavity of mice was exposed to cockroach extract. Hyperresponsiveness of airway and the allergic inflammation induced were assessed.
All the expected characteristics of asthma were found to develop in mice sensitized to cockroach through the intranasal route even in the absence of an adjuvant. These include airway hyperresponsiveness (AHR), eosinophilic airway inflammation and allergen-specific IgG1 antibodies. Immune regulator proteins called Th2 cytokines and chemokines were found elevated. These immune reactions were noticed following exposure to allergens over a period of 2 weeks.
Most of the previous studies in mice were performed by intraperitoneal injection, i.e. injection into the body cavity, in the presence of an adjuvant. Another relevance of the current study is that it focuses on the regulation of the mucosal immune system in the lung. The mucosa lining body cavities play key roles in the body’s immune mechanism. The study of mucosal immunology had been restricted to gastrointestinal diseases so far.
The new study has presented a detailed analysis of a model of allergic sensitization. This model will definitely lead us to a better understanding of the role of cockroach allergens in allergic disease and in the inner city asthma epidemic.
Reference: Mucosal exposure to cockroach extract induces allergic sensitization and allergic airway inflammation: Allergy, Asthma & Clinical Immunology 2011, 7:22 doi:10.1186/1710-1492-7-22
General Manager - Staff Entomologist