雅思阅读 157: The Leaky Barrier — Inside the Rise of Food Allergy（渗漏的屏障：食物过敏的兴起）

改编自 Nutrients / Frontiers in Allergy（2023–2026年）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://pmc.ncbi.nlm.nih.gov/articles/PMC10780391/

Reading Passage

A. A generation ago, severe reaction to ordinary food was a rarity; school cafeterias kept no emergency adrenaline pens, and a child who turned red and wheezed after a peanut was a medical footnote. Today the opposite is true. Food allergy has become common enough to reshape menus, airline policies and parenting itself, and the upward trend is too steep to dismiss as better diagnosis alone. In some affluent countries around one child in ten is now affected, a figure that has roughly doubled within a single generation, and the reactions range from a rash to a swelling of the throat that can kill within minutes. Researchers have been asking why, and their answer has migrated from a simple story — that some people's immune systems are overly excitable — toward a more structural one. The new explanation centres not on the immune system's temper but on the wall that separates it from the gut. That wall, a single layer of cells lining the intestine, normally stands guard, admitting digested nutrients while keeping undigested proteins and bacterial products out of the bloodstream. When this barrier develops small leaks, harmless food proteins slip through and are presented to the immune system in a way it reads as dangerous. The allergy, on this view, is a downstream symptom of a door that should have stayed shut.

B. The cells that line the intestine are bound together by seals called tight junctions. Think of them as the stitches holding a waterproof wall together; as long as each stitch holds, nothing passes between the cells. A family of signals controls how tight those stitches are, and one in particular, a hormone named zonulin, loosens them on purpose when the gut senses certain microbes or, in susceptible people, gluten. Under normal circumstances the loosening is temporary, a designed opening that closes again. The trouble begins when the opening becomes chronic. Scientists describe a state they call, more vividly than elegantly, a "leaky gut", in which the junctions stay too permeable for too long. Food proteins that should have been disassembled inside the gut now cross intact, reach the tissue beneath, and hand themselves to immune cells that were never meant to meet them. The theory that ties this together is known as the epithelial barrier hypothesis: a leaky wall, rather than a faulty soldier, turns a harmless meal into an attack.

C. What opens the wall, and why now? The leading suspect is the trillion-strong community of bacteria that lives in the gut — the microbiome. These resident microbes are not passive passengers; they train the immune system, consume fibre and produce chemicals that reinforce the very junctions holding the barrier shut. Beneficial bacteria churn out short-chain fatty acids, by-products of digesting fibre, which strengthen the tight junctions and calm inflammatory responses. When the community loses diversity, the opposite happens. Studies of allergic children find a microbial signature different from healthy controls: fewer of the protective species, more of the inflammatory ones, and an increase in pore-forming proteins such as claudin-2 that literally open gaps between cells. Animal experiments make the causal case sharply. Mice given broad-spectrum antibiotics lose much of their gut flora, develop a more permeable gut wall, and then become far more likely to mount an allergic reaction to an egg protein they previously tolerated. Restore the flora and, in the same animals, tolerance often returns. The implication is striking: susceptibility to a food allergen can, at least in mice, be transferred by transplanting the microbes themselves, turning what looked like a fault of the immune system into a fault of its microbial tutors.

D. This research points a finger at the surroundings of modern childhood. Antibiotics are not the only lever. Diets heavy in ultra-processed food, low in fibre, and high in additives appear to reshape the microbiome in ways that favour permeability, and caesarean birth deprives a newborn of the first dose of maternal bacteria it would normally receive. Hygiene, too, has a double edge: the cleanlier an early environment, the fewer microbial exposures the young immune system uses to learn what is safe. Researchers are careful to avoid blaming individual parents, because the pattern sits across whole populations rather than within a single family. The insight is not that cleanliness harms children, but that a developing immune system, starved of the microbial variety it expects, may misfire against the one intruder it actually meets at the dinner table. The era that gave aseptic hospitals and safe water may also, inadvertently, have narrowed the training range of the gut.

E. The practical hope lies in reversing the leak rather than just blocking the alarm. If allergy begins with a permeable wall and a deranged microbiome, then fixing the wall and restoring the microbes ought to matter as much as the adrenaline pen that treats the attack once it has happened. Early results are encouraging but cautious. Particular strains of bacteria, such as Lactobacillus reuteri, have shown in trials their ability to reinforce junctions and reduce sensitisation, and researchers speak of microbiome-based therapies that transplant the right community rather than suppress the wrong reaction. No one yet promises a cure. Children whose symptoms are severe still rely on carrying an adrenaline injector and on the vigilance of everyone around them, and oral-desensitisation therapy, though it can raise the threshold that triggers a reaction, demands months of supervised doses rather than a single fix. The honest summary is that food allergy is being reimagined from a defect in the immune system to a defect in the conversation between a person, their bacteria and the food they eat. Treating the conversation, rather than silencing the immune system, may yet turn the allergy boom of the last decades back the other way.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The steep rise in food allergy and a new way to explain it ii. How the gut wall is supposed to keep proteins out iii. The resident microbes that keep the wall sealed iv. Why antibiotics are prescribed to treat allergies v. The modern conditions suspected of weakening the wall early in life vi. The allergy vaccine that has already cured millions vii. Treating the conversation rather than silencing the alarm

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. According to the new explanation, what primarily goes wrong in food allergy? A. The stomach produces too much acid. B. The intestinal barrier becomes permeable, letting food proteins reach the immune system. C. The lungs fail to absorb oxygen. D. The liver stores too much fat.

6. What does the hormone zonulin do? A. It permanently destroys tight junctions. B. It can loosen the tight junctions between gut cells. C. It digests food proteins. D. It produces adrenaline.

7. What happened in the mouse experiments? A. Antibiotics made the gut less permeable and prevented allergy. B. Removing gut flora increased permeability and worsened allergic reactions. C. Mice became allergic to sunlight. D. The mice developed no changes at all.

8. Why do researchers avoid blaming individual parents? A. The pattern appears across whole populations rather than one family's choices. B. They have found that genes alone explain everything. C. Parents cannot be studied scientifically. D. The allergy boom has now reversed.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. The intestinal lining is normally a single layer of cells.
10. Beneficial gut bacteria produce short-chain fatty acids that reinforce tight junctions.
11. Caesarean birth gives a newborn a stronger, more diverse microbiome than vaginal birth.
12. Lactobacillus reuteri has already cured food allergy in most patients.
13. Ultra-processed diets have been shown to reshape the microbiome in ways favouring permeability.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Gut cells are sealed by (14) __________ junctions; when these stay too open, the resulting "leaky gut" lets undigested proteins reach the underlying (15) __________ and alert the immune system.

答案与解析

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