Shrimp is the most common food allergen in Asian populations and the leading cause of food-induced anaphylaxis worldwide.¹  However, some shrimp-allergic patients only react to selected seawater (SW) or freshwater (FW) shrimp and the reasons for this are unclear.¹ During the 2024 AAAAI Annual Meeting, Professor Leung, Ting-Fan from The Chinese University of Hong Kong, presented the results from a study which compared oral food challenges to SW and FW shrimps in patients with suspected shrimp allergy and identified the major allergens in these shrimps.¹

In this study, 61 Chinese patients aged 12-60 years who experienced adverse reactions within 2 hours after shrimp ingestion over the past 2 years were recruited.¹ These patients underwent double-blind, placebo-controlled food challenge (DBPCFC) with Penaeus monodon (also known as tiger prawn, a SW shrimp) and Macrobrachium rosenbergii (also known as big head shrimp, a FW shrimp).¹  While 50 patients could tolerate both SW and FW shrimps, 6 patients reacted to SW shrimps only, 2 reacted to FW shrimps only, and 3 reacted to both types of shrimps, demonstrating that patients  with immediate-onset adverse shrimp reactions could show discordant DBPCFC outcomes to SW and FW shrimp.¹

To investigate the potential cause behind the difference in DBPCFC outcomes in patients with suspected shrimp allergy, the composition and abundance of allergens from two SW (P. monodon and Litopenaeus vannamei) and two FW (M. rosenbergii and Macrobranchium nipponense) shrimps were characterized in this study.¹ Shrimp proteins were extracted from peeled shrimp meat and resolved on a 10% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gel, before transferring to a polyvinylidene fluoride (PVDF) membrane for western blotting against the diluted sera of allergic subjects to identify immunoglobulin (IgE)-reactive allergens.¹ IgE-binding protein bands were excised from the gel, digested and subjected to matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry to produce peptide mass fingerprints for identification.¹

Compared to the two FW shrimps, L. vannamei had more high-molecular weight allergens (>72kDa), and both SW shrimps, L. vannamei and P. monodon had more small proteins (<34kDa).¹ Both tropomyosin and myosin heavy chain were cross-reactive allergens in all 4 shrimps tested, with >70% of shrimp-allergic subjects reacting to tropomyosin and fewer than 20% of subjects reacting to myosin heavy chain.¹ Aside from tropomyosin and myosin heavy chain, other common allergens including hemocyanin, arginine kinase, and myosin light chain were also observed in the SW shrimp samples.¹ While M. nipponense had the lowest abundance of muscle proteins compared to the other shrimp species tested, it showed the strongest IgE binding, suggesting that it could be a highly allergenic shrimp.¹  Nevertheless, due to the small sample size, no association between allergen sensitizations and challenge-confirmed allergy to SW and FW shrimps was observed.¹

In summary, tropomyosin was found to be the major cross-reactive allergen across the 4 edible SW and FW shrimps tested.¹ Differences in allergen composition may explain the discordant DBCFC outcomes to SW and FW shrimp observed among patients with suspected shrimp allergy.¹