Thank you for your recent inquiry.
There are three issues to be considered in answering your questions. These are:
Is there evidence for cross-reactant proteins in tree nuts and peanuts?
Is there a high incidence in an atopic individual of developing allergy to both peanuts and tree nuts even though there are no cross-reactant proteins? (by this I mean, by virtue of their characteristics, are peanuts and tree nuts both "highly allergenic," and therefore allergic individuals are highly likely to develop allergies to both?).
Is the distinction between peanuts and tree nuts confusing to patients so that it is safest to suggest avoidance of both in a patient highly allergic to one?
As in many instances, based upon the available evidence, there is no definitive approach. That is, in final analysis, there is room for interpretation of available data so that clinical judgment will enter into the answer to your questions. However, based upon the literature as expressed in the information provided below, in brief, the direct answer to your questions, in my opinion, is:
Cross-reactivity does translate clinically with respect to potential symptoms.
Cross-reactivity does translate when skin testing.
The support for my answers to your questions is seen in the information that I have cited below. First of all, there are two previous answers to your questions available on the Academy's "Ask the Expert" website. For your convenience, I have copied both of these responses.One was given by Dr. Hugh Sampson at our request in 2007, and the other was presented by Dr. Burt Zweiman, who managed this website prior to 2007.
In addition, there is a quote from an excellent article by Dr. Scott Sicherer that appeared in the Journal of Allergy and Clinical Immunology in 2001.
These sources clearly state that a high percent of individuals are polysensitized and that the rate of polysensitization (regardless of cross-reacting antigens) is significant between peanuts and tree nuts.
Dr. Sampson also deals with the difficulty of distinguishing peanuts from other tree nuts that confuses patients. In addition, there is some evidence for antigenic cross-reactivity that could explain the fact that many patients are allergic to both peanuts and tree nuts from the article by De Leon, the abstract of which is copied below as well. The in vitro cross-reactivity that is demonstrated would also be reflected in skin tests.
Thank you again for your inquiry and we hope this response is helpful to you.
Cross Reactivity Antigens between Peanut and Tree Nuts
Q - If you have a toddler who is allergic to peanut supported by history and skin testing, should they empirically avoid tree nuts despite there different protein structures since we know tree nuts might be sensitizers- and vice versus, tree nut allergic....avoid peanut? What if this same tree nut-allergic toddler is enjoying peanut butter (ST neg) regularly, should we deprive him/her of continued ingestion- so he does not become sensitized?
I used to permit them to eat the species they were not allergic to but seem to recall a noted Food Allergist Expert (nameless for now) suggest NOT permitting this. (unless he meant not-yet-exposed toddlers).
How often should we retest?
What do others feel about this?
A - Thank you so much for your recent inquiry.
As editor of the “Ask the Expert” section, I have forwarded your inquiry to an expert in the area in question. As soon as we receive the answer I will forward the opinion to you.
I am sending you this just to let you know that we are in the process of seeking an answer.
Phil Lieberman, MD
Here is how I respond to similar questions from my patients:
If you have a toddler who is allergic to peanut supported by history and skin testing, should they empirically avoid tree nuts despite there different protein structures since we know tree nuts might be sensitizers- and vice versus, tree nut allergic....avoid peanut?
If a toddler has a clear-cut, recent reaction to peanut and a positive skin test, I generally tell the parents that they should eliminate peanuts and tree nuts from the child's diet. [I also obtain a peanut-specific IgE level so that I can get some idea of whether this toddler may fall into the 20% of young children who will outgrow their peanut allergy] There is little evidence to support the notion that tree nuts "cross-react" with peanuts and therefore avoidance for this reason seems unjustified. However, two other factors that support tree nut avoidance must be considered. (1) Studies indicate that about 35% of American toddlers with peanut allergy will have [or develop] concomitant tree nut allergy. (2) In a young child, it is very confusing to distinguish the difference between peanut and "safe" tree nuts, since many adults refer to both as nuts and are unaware of situations where peanuts may be included with specific tree nuts. We have seen too many accidents where a child receives peanut-containing products because of misidentification, cross-contamination, or substitution with some peanut product. Consequently we think it is safer to avoid tree nuts until the child is old enough to understand the nuances of avoiding peanut contaminated foods. We often will skin test the child to various tree nuts [and obtain nut-specific IgE if the skin test is positive] so that the parents will know whether the child is likely to experience an allergic reaction if the child inadvertantly ingests a tree nut-containing food.
What if this same tree nut-allergic toddler is enjoying peanut butter (ST neg) regularly, should we deprive him/her of continued ingestion- so he does not become sensitized?
In such a toddler, I would allow him/her to continue to ingest peanut butter. By and large, tree nuts are considerably more expensive than peanuts and therefore are rarely substituted for peanuts in various products. However, I always advise caution.
Hugh A. Sampson, MD FAAAAI
Mt. Sinai School of Medicine
Cross-reaction between peanuts and walnuts
Q - In children with known peanut allergy is there any cross reactivity with walnuts? Should we restrict processed foods with nuts other than peanuts?
A - Peanuts, as legumes, do not cross-react with true (tree) nuts such as walnuts in IgE-mediated allergic reactions. However, in their very extensive experience with food allergies, Sampson's group in New York has found that about 35% of their peanut-allergic children subsequently manifested allergies to one or more tree nuts. Therefore, I would be quite cautious about introducing tree nuts in the diet of peanut-allergic children. You may wish to have the child have allergy skin tests to the various tree nuts before allowing them in the diet. If the tree nuts are ingested by the test-negative child, it may be prudent to start with very small amounts and increasing gradually as tolerated. If the child exhibits a negative response to appropriate tree nut skin tests by a qualified allergist, then it is quite unlikely that the child will exhibit an immediate (IgE-mediated) systemic reaction to the small amounts of those tree nuts present in processed foods
Immunological analysis of allergenic cross-reactivity between peanut and tree nuts DE LEON M. P. (1 2) ; GLASPOLE I. N. (1 2 3) ; DREW A. C. (1 2 3) ; ROLLAND J. M. (2 3) ; O'HEHIR R. E. (1 2 3) ; SUPHIOGLU C. (1 2 3) ; (1) Department of Allergy, Immunology and Respiratory Medicine, The Alfred Hospital, Monash University, Commercial Road, Melbourne, Victoria 3004, AUSTRALIE
(2) Department of Pathology and Immunology, Monash University, Commercial Road, Melbourne, Victoria 3004, AUSTRALIE
(3) Co-operative Research Centre for Asthma, Sydney, AUSTRALIE
Background Peanut and tree nut allergy is characterized by a high frequency of life-threatening anaphylactic reactions and typically lifelong persistence. Peanut allergy is more common than tree nut allergy, but many subjects develop hypersensitivity to both peanuts and tree nuts. Whether this is due to the presence of cross-reactive allergens remains unknown. Objective The aim of this study was to investigate the presence of allergenic cross-reactivity between peanut and tree nuts. Methods Western blotting and ELISA were performed using sera from subjects with or without peanut and tree nut allergy to assess immunoglobulin E (IgE) reactivity to peanut and tree nut extracts. Inhibition ELISA studies were conducted to assess the presence of allergenic cross-reactivity between peanut and tree nuts. Results Western blot and ELISA results showed IgE reactivity to peanut, almond, Brazil nut, hazelnut and cashew nut for peanut- and tree nut-allergic subject sera. Raw and roasted peanut and tree nut extracts showed similar IgE reactivities. Inhibition ELISA showed that pre-incubation of sera with almond, Brazil nut or hazelnut extracts resulted in a decrease in IgE binding to peanut extract, indicating allergenic cross-reactivity. Pre-incubation of sera with cashew nut extract did not cause any inhibition. Conclusion These results show that multiple peanut and tree nut sensitivities observed in allergic subjects may be due to cross-reactive B cell epitopes present in different peanut and tree nut allergens. The plant taxonomic classification of peanut and tree nuts does not appear to predict allergenic cross-reactivity. Clinical and experimental allergy ISSN 0954-7894 2003, vol. 33, no9, pp. 1273-1280 [8 page(s) (article)] (31 ref.)
"Legumes, tree nuts, and seeds Cosensitization to allergenic foods, such as peanut, tree nuts, and seeds (sesame, poppy, and mustard) is common. In a study of 731 subjects in the United Kingdom, 59% sensitized to peanut were also sensitized to hazelnut, Brazil nut, or both.26 Although clinically significant cross-reacting proteins have not yet been described, coallergy to peanut and tree nut has been reported between 23% and 50% in referral populations of atopic patients.16, 24, 31, 32 The rate of coallergy is much lower in unselected populations (2.5%).33 The clinician must consider the age of the patient, history, and perhaps sensitization in considering categoric elimination of these allergenic foods.34 Reactions to seeds, such as sesame, mustard, and poppy, are reported,27, 35, 36 and cross-reactivity with foods (hazel, kiwi, and other seeds) and pollens is potentially important, but the full clinical implications are far from established."
SOURCE: Sicherer S:Clinical implications of cross-reactive food allergens, J Allergy Clin Immunol
Volume 108, Issue 6, Pages 881-890 (December 2001)
Phil Lieberman, M.D.