In general, although there is extensive immunologic (in vitro) antigenic cross-reactivity between legumes in general (including peas and peanuts), you are correct in that clinical cross- reactivity is unusual as discussed in Scott Sicherer’s hallmark review of food allergy cross-reactivity (1). However, unfortunately, wherever such antigenic cross-reactivity occurs, there is potential for clinical cross-reactivity as well. And the in vitro cross-reactivity between pea and peanut is no exception to this general observation; and clinical cross-reactivity has been demonstrated in rare instances (for what is probably the best example of this, see abstract copied below).
Therefore, as is really always the case, the only true test of clinical reactivity is an oral food challenge, and one could not say, cart blanch, that your patient would not react to the butter of golden pea.
Thank you again for your inquiry and we hope this response is helpful to you.
J Allergy Clin Immunol. 2003 Feb;111(2):420-4.
Patients with anaphylaxis to pea can have peanut allergy caused by cross-reactive IgE to vicilin (Ara h 1).
Wensing M, Knulst AC, Piersma S, O'Kane F, Knol EF, Koppelman SJ.
Department of Dermatology/Allergology G02.124, University Medical Centre Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
Background: Serologic cross-reactivity among legumes has been described; however, it is rarely clinically significant. In this study 3 patients with a history of anaphylaxis to pea are described who subsequently had symptoms after ingestion of peanut.
Objective: We investigated whether the peanut-related symptoms were due to cross-reactivity between pea and peanut proteins.
Methods: Peanut-related symptoms were documented according to case history or double-blind, placebo-controlled food challenge results. Skin prick tests were performed, and specific IgE levels were determined for pea and peanut with the CAP system FEIA. IgE-binding proteins in pea and peanut were identified by using immunoblot analysis. Cross-reactivity was studied by means of immunoblot and ELISA inhibition studies with whole extracts and purified allergens.
Results: Peanut-related symptoms consisted of oral symptoms in all patients, with additional urticaria and dyspnea or angioedema in 2 patients. All patients had a positive skin prick test response and an increased IgE level to pea and peanut. Immunoblotting revealed strong IgE binding to mainly vicilin in pea extract and exclusively to Ara h 1 in crude peanut extract. Immunoblot and ELISA inhibition studies with crude extracts, as well as purified proteins, showed that IgE binding to peanut could be inhibited by pea but not or only partially the other way around.
Conclusion: Clinically relevant cross-reactivity between pea and peanut does occur. Vicilin homologues in pea and peanut (Ara h 1) are the molecular basis for this cross-reactivity.
1. Sicherer S. Clinical implications of cross-reactive food allergens. J Allergy Clin Immunol 2001; 108(6):881-890.
Phil Lieberman, M.D.