It’s my birthday tomorrow and I am very fortunate to have been given a lovely birthday present by one of the best scientists I know…a guest blog! It may just be in my world, but all the best friends share science for celebratory events, and so I’m excited to share this one with you.

If any of you have ever attended a conference or event with me, you’ll know my body and I don’t always get on, I am intolerant to many things and so food can be challenging. Claire, as an immunologist, has a lot of specialist knowledge about intolerance and allergies, and puts you with me always trying to learn more. I ask her ‘why’ a ridiculous amount of times. To aid, not just me, in this she has written a post that talks about allergy works the way it does, when to many of us the process is somewhat baffling.

Dr Claire Walker has been a paid up member of the Dream Team since 2013, token immunologist and occasional defector from the Immunology Mafia. Registered Clinical Scientist in Immunology with a background in genetics (PhD), microbiology and immunology (MSc), biological sciences (mBiolSci), education (PgCert) and indecisiveness (everything else). Now a Senior Lecturer in Immunology at University of Lincoln. She has previously written many great guest blogs for The Girlymicrobiologist, including one on turning criticism into a catalyst for change.

Blog by Dr Claire Walker

I love teaching allergy. As a Clinical Scientist in Immunology, we all have stories about the wonderful world of hypersensitivity. One Christmas Eve, an urgent request arrived in our laboratory for allergy testing to chocolate in a two-year-old. With Christmas Day looming, it was one of those samples you couldn’t help but become invested in and, to everyone’s relief, the result was negative. Christmas was saved! Most of us know someone with an allergy, from the friend who spends every summer sneezing through hay fever to the person who carries adrenaline because a trace of the wrong food could cause anaphylaxis. Few areas of immunology run such an extraordinary gamut in presenting symptoms whilst sharing a sole underlying pathophysiology. But what fascinates me most is the strange logic behind some of these reactions. Why can someone eat wheat unless they exercise afterwards? How can a tick bite make you allergic to red meat? And why might a house dust mite look remarkably like a prawn?

So, what actually is an allergy? It occurs when the immune system reacts to something normally harmless, such as pollen or food. In many allergies, an antibody called IgE recognises part of an allergen and triggers immune cells to release chemicals including histamine. Symptoms range from sneezing and itching to life threatening anaphylaxis. This differs from an intolerance, where the immune system isn’t driving the reaction. Lactose intolerance, for example, results from difficulty digesting lactose. Intolerances are fascinating too, but that’s one for another post.

Let’s start with perhaps the most familiar allergy, hay fever. It is easy to dismiss it as a minor inconvenience, but its timing is particularly unfortunate for teenagers. The UK grass pollen season coincides with GCSE examinations, just when concentration and sleep really matter. A study of 1,834 UK teenagers by Walker and colleagues (no relation!) found that those experiencing allergic rhinitis symptoms during their exams had 40% higher odds of unexpectedly dropping a grade between their winter mocks and summer exams. For those taking sedating antihistamines, the odds were 70% higher. Hay fever may be commonplace, but its effects can be far from trivial.

Now for one of my favourite examples of the peculiar logic of allergy: wheat dependent exercise induced anaphylaxis, or WDEIA. Imagine being able to eat toast without a problem and go for a run without a problem but combine the two and you can have a potentially life threatening allergic reaction. People with WDEIA are commonly sensitised to a wheat protein called omega-5-gliadin, but a reaction may only occur with a cofactor. Exercise is the classic example, although alcohol and anti-inflammatory drugs such as ibuprofen can also play a part. This makes WDEIA difficult to spot because the food responsible may have been eaten many times without incident. A UK study of 132 patients found that more than two thirds had waited at least a year for the correct diagnosis. Sometimes in immunology, it really is all about context.

Occasionally allergy feels less like laboratory medicine and more like detective work. One of my favourite cases, presented by Scottish colleagues at a conference some years ago, involved a little boy who mysteriously developed anaphylaxis only when he stayed with his grandparents. At home he was completely well. His parents were strict vegans, which eventually provided the vital clue. What was Grandma putting in those pies? Meat. Mammalian meat allergy, or alpha gal syndrome, is one of the strangest food allergies we encounter. Unlike most food allergies, IgE recognises a sugar called alpha gal, found in most mammals but not humans and other higher primates. Remarkably, sensitisation can follow a tick bite. Reactions to beef, pork or lamb can then occur several hours after eating, making the culprit particularly difficult to identify. In 2021, the first three cases linked to tick bites acquired in the UK were reported. One patient, a gardener who had experienced more than 100 tick bites, described reactions two to eight hours after foods including pork, roast beef and, appropriately, steak and kidney pie. When the trigger is a tick bite and the reaction comes hours after Sunday lunch, joining the dots is anything but straightforward.

And now to the question on everyone’s lips: when does a dust mite actually look like a prawn? To the untrained eye, obviously never. To an IgE antibody, however, they can look surprisingly similar. Antibodies recognise specific molecular structures, and if sufficiently similar structures occur elsewhere in nature, they can recognise those too. This is cross reactivity. House dust mites and crustaceans such as prawns share a protein called tropomyosin, allowing IgE against mite tropomyosin to cross react with shellfish. To our immune system, the distance between the bedroom and the seafood platter can be surprisingly small. An equally curious relationship exists between natural rubber latex and fruits including avocado, banana and kiwi, known as latex fruit syndrome. Again, the connection comes from related proteins found in both latex and plants. These unexpected relationships are a wonderful reminder that allergens are not defined by where they come from, but by the molecular structures our antibodies recognise.

It’s this wonderfully weird logic that makes allergy such a joy to teach. Microbiology may have its charms, but can a bacteria make a dust mite look like a prawn? I rest my case.

(Note from Girlymicro – although I accept Claire’s idea that the prawn dust mite confusion is interesting, microbiology includes Tardigrades, need I say more! The war of which is the best discipline continues 🙂

All opinions in this blog are my own