Allergies to cross-reactive plant proteins. Latex-fruit syndrome is comparable with pollen-food allergy syndrome.

Both latex-fruit syndrome and oral allergy syndrome concomitant with pollinosis (pollen-food allergy syndrome) are considered to be caused by cross-reactivity between sensitizers and symptom elicitors. The cross-reactive food allergens relevant to these syndromes are mostly sensitive to heat and digestive enzymes. Such a vulnerable antigen cannot sensitize people perorally but provokes allergic reactions in already sensitized patients based on its cross-reactivity to the corresponding sensitizer. These types of food allergens are often called incomplete food allergens or nonsensitizing elicitors. Their features contrast with those of complete food allergens that have the capacity for peroral sensitization as well as symptom elicitation. Although highly antigenic and cross-reactive, carbohydrate epitopes do not generally elicit allergic reactions and often disturb in vitro IgE tests. Recent research has revealed that some of the cross-reactive allergens responsible for the two syndromes are proteins related to the defense responses of higher plants. Plant defense-related proteins are relatively conserved in the course of evolution and can supply cross-reactive epitopes. It is important to note that various stresses can stimulate the expression of these proteins, which implies that allergens increase in plants under stressful conditions like severe growing situations and exposure to some kinds of chemicals. Because defense-related proteins usually provide a plant with resistance to stresses, varieties that are apt to intensively induce such proteins are agriculturally valuable. Less toxic substances that cause crops to express defensive proteins are being investigated as a new type of agrochemical. Moreover, some defense-related proteins are going to be constantly produced in genetically modified plants. Even though these proteins can be useful agriculturally, their allergenicity should be evaluated carefully.