Shrimp Serology: We Need Tests with More and Less Cross-reactivity

Abstract

with a positive skin test to shrimp extract, of whom 58 were established to be allergic. IgE to a panel of 10 recombinant crustacean allergens (mostly muscle proteins) was tested in a dot-blot assay. As expected, tropomyosin was the dominating component being positive not only in 83% of the 58 allergic subjects but also in 44% of the 16 tolerant subjects. Its false-negativity rate of 17% is disappointing and intriguing. Of the other components tested, arginine kinase had the highest sensitivity (48%), followed by myosin light chain (38%) and sarcoplasmic calcium-binding protein (34%). However, even with the complete panel the false-negativity rate was still 12%. This deficiency of the panel could be due to technical problems with the expression of the recombinant proteins, but could also reflect species differences. Lured by the high cross-reactivity of tropomyosin, we might be tempted to assume erroneously that our immune system is unable to distinguish invertebrates. An illustrative example to the contrary is the limited cross-reactivity of the major mite allergens. THE 4 DIMENSIONS OF ALLERGY DIAGNOSIS The first dimension is diagnostic sensitivity: the ability to identify more than 95% of the patients with allergy to the source in question. Cross-reactivity is convenient for shrimp allergy diagnosis, because of the many different shrimp species that patients may be exposed to. Without cross-reactivity, we would need to test for reactivity to all these species. From this perspective, it is a positive feature that the cross-reactivity amongst invertebrate tropomyosins is very high. On the other hand, more than 10% of the shrimp-allergic patients were found to be negative for tropomyosin. Because positivity to shrimp extract was the inclusion criterion, the potential exclusion of some patients may even have resulted in a too optimistic estimate of test sensitivities. It might be worthwhile to look for other cross-reactive shrimp allergens that might be used alone or in combination with tropomyosin to achieve a higher diagnostic sensitivity. The other 3 dimensions are all related to specificity. The second dimension is the ability to distinguish between sensitized subjects with allergy and those without allergy. Exposure to a cross-reactive substance is often (but not always, see below) better tolerated than exposure to the sensitizing substance. In the present study population 11 (as in other studies 4 ), almost all shrimp-allergic patients were sensitized to mites. It would be interesting to know how many of these mite-sensitized patients were mite-tolerant and negative for the major group 1 and group 2 mite allergens. The third dimension is the ability to distinguish between allergen source materials that do or do not induce symptoms. In the case of shellfish allergy, it is generally assumed that consumption of all species of invertebrates should be avoided. In view of the promotion of invertebrate meat sources as an alternative for mammalian meat, the general validity of this approach is under scrutiny. In a fish allergy study, consumption of crossreactive fish species was in some cases well tolerated. 12