Walnut protein Jug r 4 and allergy testing in adults
What it found
A walnut protein called Jug r 4 was linked to allergy in 27% of allergic adults tested.
Nine out of ten people who reacted to it in a blood test truly had a walnut allergy.
What they found
Studies in people
Jug r 4 as allergen
Lab tests on blood from eight allergic adults showed their immune systems reacted to a walnut protein called Jug r 4. This protein was then checked across the full group of 55 adults.
How common it is
Out of the 33 adults confirmed to have a walnut allergy, about 27% showed an immune response to Jug r 4. None of them reacted only to Jug r 4, as most also reacted to another walnut protein called Jug r 1.
Accuracy of testing
When a line blot test found Jug r 4 in someone's blood, there was a 90% chance they truly had a walnut allergy. Only one person with a positive test result could actually eat walnuts without symptoms.
Cross-reactions with nuts
People whose blood reacted to Jug r 4 often reacted to similar proteins in hazelnuts, cashews, peanuts and soybeans. Six out of ten reacted to the hazelnut version, possibly because these proteins share a similar shape.
Other findings
Missing from test kits
Lab analysis showed that Jug r 4 was absent from a widely used commercial walnut allergy test extract. The authors suggest this might be because the protein does not dissolve easily in the liquids used to make the kit.
What the authors conclude
- They conclude that the walnut protein Jug r 4 is a relevant but minor allergen found in about 27% of walnut allergic adults.
- They note that testing for Jug r 4 has a high accuracy for confirming a true walnut allergy when the test is positive.
- They point out that Jug r 4 is missing from a standard commercial test extract, which could lead to missed diagnoses.
How it was done
Earlier allergy tests using three known walnut proteins could not explain every case of walnut allergy. The authors wanted to find other walnut proteins that trigger reactions so diagnosis could improve.
They studied 55 adults suspected of having a walnut allergy, including 33 who were confirmed allergic and 22 who tolerated walnuts. They used blood samples and lab methods to look for immune responses to different walnut proteins. Each person also ate measured amounts of walnut under medical supervision to confirm their allergy status.
What it can’t tell you
- This study looked at adults with suspected allergies, so the results may not apply to children or people eating walnuts normally.
- Because everyone who reacted to Jug r 4 also reacted to other walnut proteins, scientists cannot yet tell if Jug r 4 alone causes symptoms.
- The group included only 55 people, so larger studies are needed to confirm how reliable this test is for everyone.
Who paid
- Authors work at
- University Medical Center Utrecht, The Netherlands; Magna Graecia University of Catanzaro, Italy
The paper
- Title
- A subset of walnut allergic adults is sensitized to walnut 11S globulin Jug r 4
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Blankestijn MA, den Hartog Jager CF, Blom WM, et al (2018). A subset of walnut allergic adults is sensitized to walnut 11S globulin Jug r 4. Clinical and experimental allergy. doi:10.1111/cea.13208Free full textPubMed 29904971DOI
Summary written 1 Oct 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error