Type I hypersensitivity in an asthmatic child allergic to peanuts: was soy lecithin to blame?

BACKGROUND: Soy lecithin is widely used as an emulsifier, not only in topical skin care products but also in various drugs administered either topically, orally, or intravenously or by inhalation. Patients strongly allergic to soy and/or peanuts can develop an anaphylactic reaction when exposed to soy lecithin. METHOD: We report a 3-year-old asthmatic boy, allergic to peanuts, who was treated at the emergency department for an exacerbation of asthma following an upper respiratory tract infection. Within an hour after receiving the second of two inhalations of an ipratropium bromide (Atrovent) metered dose inhaler, he developed respiratory distress and generalized urticaria, an adverse event that regressed within 48 hours of withdrawal of the suspected drug. Soy lecithin, contained as an excipient in the metered dose inhaler, was strongly suspected of being responsible for this reaction. CONCLUSION: Drug products containing soy lecithin can cause severe allergic reactions in patients allergic to peanuts or soy. Physicians should be aware that adverse drug reactions can be due to both the active medical component and the excipient ingredients.

P39, a novel soybean protein allergen, belongs to a plant-specific protein family and is present in protein storage vacuoles.

Soybean lecithins are seeing increasing use in industry as an emulsifier and food additive. They are also a growing source of human food allergies, which arise principally from the proteins fractionating with the lecithin fraction during manufacture. A previous study (Gu, X.; Beardslee, T.; Zeece, M.; Sarath, G.; Markwwell, J. Int Arch. Allergy Immunol. 2001, 126, 218-225) identified several allergenic proteins in soybean lecithins and a soybean IgE-binding protein termed P39 was discovered. However, very little was known about this protein except that it was coded by the soybean genome. This paper investigates key biological and immunological properties of this potential soybean lecithin allergen. P39 is encoded by a multigene family in soybeans and in several other higher plants. The soybean P39-1 protein and its essentially indistinguishable homologue, P39-2, have been cloned and studied. These proteins and their homologues belong to a family of plant-specific proteins of unknown function. In soybeans, P39-1 is seed specific, and its transcript levels are highest in developing seeds and decline during seed maturation. In contrast, P39 protein was detectable only in the fully mature, dry seed. Subcellular fractionation revealed that P39 protein was strongly associated with oil bodies; however, immunolocalization indicated P39 was distributed in the matrix of the protein storage vacuoles, suggesting that association with oil bodies was an artifact arising from the extraction procedure. By the use of recombinant techniques it has also been documented that IgE-binding epitopes are present on several different portions of the P39-1 polypeptide.