Litchi chinensis is a tropical fruit belonging to the Sapindaceae family, in which a 16 kDa allergen (Lit c 1) has just been identified (1), corresponding to a profilin.
There are currently very few studies which describe adverse reactions after ingestion of lychee (1–6) and the majority of these describe a concurrent sensitization to plants from the Compositae family. However, the possible existence of cross-reactivity between both allergenic sources has not been studied.
We describe two patients (case a, case b) with anaphylaxis after the first ingestion of lychee fruit. They were previously diagnosed of respiratory allergy to Compositae pollen (Artemisia vulgaris among others) and food allergy to sunflower seed.
A lychee extract (10% w/v) was prepared from raw lychees for in vivo and in vitro analyses.
Prick–prick test with lychee and skin-prick test with other commercial foods and aeroallergens showed positive results for lychee, Artemisia pollen, sunflower seed, pistachio nut and different pollens in both cases. Serum immunoglobulin (Ig) E detection (CAP-System, Pharmacia, Uppsala, Sweden) was positive, among others, for Artemisia pollen (33.6 kU/l) and sunflower seed (0.88 kU/l) in one case (a), and for lychee (0.45 kU/l) and Artemisia pollen (2.62 kU/l) in the other case (b). Provided that the diagnostic performance of the CAP for some vegetable allergens is limited, we could not carry out CAP-inhibition assays of lychee in order to quantify cross-reactivity among Artemisia pollen, sunflower seed and lychee.
To support the diagnostic procedure, in vitro cellular stimulation test: basophil activation test (BAT), antigen-specific sulphidoleukotriene production test (CAST) and histamine release test (HRT) were performed with lychee (0.3 and 0.15 μg/ml), Artemisia pollen (1.5 and 0.4 μg/ml) and sunflower seed (1.25 and 0.3 mg/ml) for FAST and sLT, and with the higher concentration of protein for HRT.
Cellular stimulation tests were positive in both cases for lychee, Artemisia pollen and sunflower seed in all of the concentrations tested with the exception of sunflower seed at the lowest concentration for BAT and CAST techniques in one case (a).
In addition, negative results were obtained using these three techniques for the same concentrations of tested allergens in five control patients.
Lychee, Artemisia pollen and sunflower seed allergens were characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunodetection in both cases.
Electrophoresis showed a pattern of protein bands within a range of molecular weight of 24–70 kDa in the three extracts. A protein band of approximately 70 kDa was recognized by serum IgE antibodies of both patients in lychee, Artemisia pollen and sunflower seed extracts. The inhibition of the immunodetection by means of the preincubation with Artemisia pollen extract (allergen in liquid phase) disabled specific IgE union to this lychee protein but was not enough to inhibit completely itself nor the 70 kDa protein in sunflower seed (Fig. 1).
A new allergen of 70 kDa protein identified in lychee and also present in Artemisia pollen and sunflower seed, is a possible candidate of the cross-reactive mechanism among Compositae family and lychee fruit. This protein has not been reported as an allergen up till now.
To our knowledge, there have only been six studies in which cases of allergy to lychee were reported. In one of these (1) a 16 kDa profilin (Lit c 1) was identified, which cross-react with that of Compositae plants, including sunflower seed. Niggemann et al. (2) described a case of cross-reactivity between lychee and latex by CAP inhibition but without identifying the responsible allergen.
In the other four cases published (3–6) only a description of the reactions which occurred after lychee ingestion was given but no mention was made of the allergenic proteins responsible for these.