“Chickens ‘unlock allergy secrets’”, reported BBC News on Saturday, saying that “scientists have turned to chickens to help them understand why some people are struck down by severe allergies”. According to the BBC, research carried out by scientists at King’s College London found that chickens have a “fossilised version of the key molecule responsible for severe allergic reactions in humans”. The findings from this laboratory study contribute to knowledge of the immune system, and may one day lead to treatments for severe allergic reactions. However, these are a long way off.
Dr Alexander Taylor and colleagues from King’s College London carried out this research. The authors are supported by grants from the Medical Research Council and the Biotechnology and Biological Sciences Research Council. Their study was published in the peer-reviewed medical journal: The Journal of Biological Chemistry .
This was a laboratory study of antibodies from chickens. The researchers were interested in exploring the relationship between a particular antibody in chickens (IgY, also found in amphibians and reptiles) and antibodies in humans (IgE and IgG). IgY appears to have similar effects to both IgE and IgG, which are involved in the defence against infection, and also in responses to allergens. Genetic studies have shown that between 310 and 166 million years ago, the ancestral form of the gene encoding an ancestral IgY-like antibody was duplicated, and these two genes gradually differentiated into the genes that encode IgE and IgG, the two types of immunoglobin seen in mammals today.
Modern IgY is thought to be the most similar molecule to the ancestral antibody, and this makes it useful for investigating how mammalian antibodies evolved to have different functions. Although IgY has molecular features that are common to both IgG and IgE, its structure is most like IgE. Certain cells in the human immune system – mast cells and basophils – bind strongly to IgE (i.e. they have a high affinity for IgE). Particular regions of the molecular structure of IgE are responsible for this tight binding. Similar regions are found in IgY but not IgG, and binding between IgG and immune cells is less strong. When IgE binds to mast cells and basophils it induces a rapid response to destroy invading cells, called degranulation. This response triggers the allergic reaction and can potentially lead to life-threatening anaphylaxis.
The researchers wanted to further their understanding of how these bonds work. To do this, they looked at how tightly IgY from chickens binds to one type of chicken white blood cell (monocytes), to see whether it was more similar to IgE or IgG. They also looked at whether deleting regions of IgY (which in IgE are known to increase the binding strength between IgE and mast cells) would affect the strength of the binding between the IgY and the white blood cells.
The researchers found that IgY bound to white blood cells less strongly than between IgE and white blood cells, but with similar strength to what has been seen with IgG. In IgY, removing the region known to be important for binding in IgE did not affect the strength of binding between IgY and the white blood cells.
The researchers say that part of the immunoglobin molecule in birds has survived for millions of years, and has evolved into a binding site responsible for the particularly high affinity and slow dissociation of IgE molecules implicated in anaphylactic responses in humans.
This complex laboratory study contributes to knowledge about the evolution of the mammalian immune system. Further research into the function of the immune system may be prompted by the findings here. Although this may eventually lead to treatments for anaphylactic shock or allergic reactions, this study does not suggest any immediate ways in which they can be tackled.
Promising, but a long way off.