Clinical Information

Allergies to tree nuts are relatively prevalent and can result in severe reactions. The main culprits in tree nut allergies include walnut, almond, pistachio, cashew, pecan, hazelnut, macadamia, Brazil nut, and pine nuts. Tree nut allergy often appears in young children and estimates of prevalence range from 0.1% to greater than 5% of the population, dependent on geographical region.

In the case of nut-induced allergic reactions, as with many other foods, symptoms usually present within minutes of ingestion. Over 80% of reactions to tree nuts involve allergy related respiratory symptoms. Tree nut allergies are one of the most dangerous types of allergic reaction with 20% to 40% of cases of related anaphylaxis, and 70% to 90% of fatalities attributable to nut exposure (including peanut exposure).

Walnut is a relatively common cause of allergic reactions to tree nuts with an overall population occurrence of 0.7%. Allergy to walnut is often persistent over a lifetime and can be severe. Walnuts can cause sensitization by means of walnut pollens/dust particles in processing industries. Allergy related common symptoms observed are nausea, vomiting, pruritus, abdominal pain, urticaria, angioedema, diarrhea, asthma, and anaphylaxis. Walnuts and pecans are related species, and there is significant potential for cross-reactively between them.

Jug r 1 is a prevalent component protein associated with systemic walnut allergy. In a study observed among patients with systemic allergic reactions to walnuts (n=16), 75% showed IgE binding to Jug r 1, Jug r 1 is the most specific and has the highest positive predictive value for walnut allergic and, thus, is considered the major component protein for walnut allergy diagnosis.  It is a persistent storage protein component (2s albumin) that is both heat and digestion stable. Cross-reactivity of 2S albumins with those of other plant sources, such as black walnut, Brazil nut, pecan, mustard, Corylus (common hazel), and sesame, may occur.

Jug r 3 is a lipid transport protein (LTP) that is also a major allergen in walnut. This protein is resistant to heat/digestion. This component allergen is associated with the risk of severe reactions (food-induced contact urticaria, oral allergy syndrome, gastrointestinal symptoms, and anaphylaxis). Approximately 75% of individuals with walnut allergy show reactivity to this component.

Significant association of the presence of IgE antibodies between Jug r 3 (walnut) and Cor a 8 (hazelnut) suggests potential for co-sensitization. Other foods that contain LTP proteins, such as peach, cherry, hazelnut, almond, and peanut (Ara h 9 component) may also exhibit cross reactivity and co-sensitization to individuals with IgE antibodies against Jug r 3.

Positive antibody to total walnut specific test results may be observed with concurrent negative Jug r 1 and Jug r 3 component protein antibody test results when there is sensitization to other walnut component proteins and/or pollens containing profilins and other proteins.