24 July 2018
This article originally appeared in the winter 2018 issue of Allergy Today.
The Malaghan Institute’s Professor Franca Ronchese explains how exposure to allergens may prevent us becoming allergic to them.
What makes us allergic? It’s a simple question, but the answer is more complicated than you might think. Things like pollen don’t ‘make’ us allergic – they’re the things our immune system overreacts to – an allergen.
What makes us allergic is exposure – exposure to an allergen like nuts, bacteria or pollen. If our immune system hasn’t encountered it, we can’t develop sensitivity to it.
This line of thinking naturally leads us to assume that avoiding a potential allergen, whether it’s in our food or our environment, is the best course of action. In reality, things aren’t that simple.
Professor Franca Ronchese, head of the immune cell biology team at the Malaghan Institute of Medical Research has spent decades studying the subtle relationship between allergens and our immune system. Prof Ronchese paints a more complicated picture of our relationship with allergens. She explains why minimising exposure to allergens is an unfortunate necessity for those suffering from allergic disease, but the opposite might prevent allergies in the first place.
In short, we need to learn to live with our allergens.
Why cleanliness does not always equal godliness
The way we live has changed dramatically in the last century. We live in cleaner, more sterile environments than ever before. Getting rid of bugs, germs and parasites might sound pragmatic, lowering our chances of infection and disease. But while we’re living ‘healthier’ lives, have we traded cleanliness for susceptibility to allergies?
“Today, we mostly live in urban environments with a much cleaner lifestyle with fewer infections, but we’re no longer exposed to bacteria as often as we once were. Even our pets are becoming allergic.” says Prof Ronchese “Just think back to what a European farming lifestyle was seventy or eighty years ago. Those people tended to not develop allergies, probably because they were regularly exposed to high numbers of bacteria from living in close proximity to their farm animals.”
What’s more, we’re finding this exposure is crucial in childhood – it’s early during life that you have to be exposed for our immune system to be conditioned and build protection from allergies.”
The story hidden in our genes
Our genetic information tells the story of our complex relationship with infections. Bacteria, parasites and allergens have been around as long as we have and have influenced our immune system and therefore the genes that control its workings.
Yet, while infectious diseases have been around throughout human history, allergies have exploded only recently. This change has been too fast to be explained by changes in our genes, and this is why we think that changes in lifestyle, not in our genes, are the likely cause of increased allergies.
“Still, genes can play a role,” says Prof Ronchese. “We know that allergies tend to run in families, which means that genes that are passed down through generations must be involved. However, there seem to be many different genes contributing to allergy, and the result is that the combined effect of all these genes together is difficult to predict.
“Because allergens seem to be hard for our body get rid of, they end up triggering the immune system in multiple ways. We can track how the immune system responds, by seeing which genes are stimulated during an allergic reaction.”
Interestingly, we find that the genes that are stimulated can be different depending on which allergen we use. For example, the work of PhD student Kerry Hilligan at the Malaghan Institute has demonstrated that certain key molecules (like TSLP and type 1 interferon) both act on the dendritic cells of our immune system, even if they have very different downstream impacts.“
So, while an immune reaction to parasites and eczema may look very different on the outside, there is a subtle commonality underpinning it all. By watching how allergens interact with the immune system, researchers like Kerry gain vital clues into how to manipulate this relationship for our collective benefit.
Why avoidance isn’t the best strategy (for some)
“Avoiding or minimising exposure to the culprit allergens once an allergy has developed is important,” says Prof Ronchese, “but in contrast, trying to prevent allergies developing by avoiding anything that could be an allergen is just not possible. It may even have the opposite effect, making us more susceptible. This is especially important when we’re young and our immune system is learning to adapt to the outside world and recognise what is good and what is bad.”
Prof Ronchese says we need to learn how to live with allergens, and to do this we need a better understanding of how allergies develop, and turn it to our favour.
“The work we do here is trying to understand how allergens change our immune system when we are exposed to them. If we can understand this, then we may be able to find ways to minimise their impact without having to live with infections or potential allergens – the best of both worlds.”