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.
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.
exposure to cockroach extract induces allergic sensitization and allergic
airway inflammation: Allergy,
Asthma & Clinical Immunology