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A Role for Glycans in Bla g 2 Cockroach Allergen-Induced Allergic Responses

Introduction

Cockroaches are a source of allergens that are capable of driving allergic respiratory symptoms, and which can lead to an increased risk for asthma. Immune responses triggered by cockroach allergens are most common among low-income urban populations in the United States, and studies have demonstrated cockroach allergen to be present in 85% of inner-city American homes.

So far, little is known about the mechanisms that are responsible for the allergic sensitization to cockroach allergens among both adults and children.

In this paper, Danh and colleagues focused their attentions on glycans – complex sugar moieties – which, according to recent evidence, are responsible for triggering allergic immune responses in subjects sensitized to cockroach allergens.
Specifically, they investigated the role that N-glycans from the Bla g 2 allergen can play in IgE antibody binding and the induction of histamine release from basophils in cockroach allergic individuals.

As Bla g 2 has been identified as one of the key cockroach allergens to elicit IgE responses, a better understanding of how Bla g 2 can elicit an immune response could contribute to fight the virulence factors in cockroach allergens.

Results

Cockroach whole body extract was separated by SDS-PAGE, and was stained for glycoproteins. N-glycans were then analysed by MALDI-MS, which confirmed the presence of many carbohydrate moieties associated with allergic immune responses.

In order to confirm the role played by such moieties in triggering an immune response, the binding of Bla g 2 or deglycosylated Bla g 2 to German cockroach specific IgE antibody was investigated in allergic individuals. As expected, deglycosylated Bla g 2 showed a significant reduction in the levels of IgE binding, confirming the role played by carbohydrate moieties in eliciting an immune response.

Interestingly, glycans were also shown to cause inhibition of histamine release and IL-4 secretion from basophils.
Finally, flow cytometry showed that basophils isolated from blood samples were able to uptake Bla g 2 when co-cultured with Lighting-Link® Fluorescein-labeled Bla g 2.

Conclusion

N-glycans have been identified as major players for allergen binding to IgE antibody in subjects sensitized to cockroach allergens. However, despite causing a strong response from IgE antibodies, they do not cause histamine release and IL4 production from basophils.

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