To the Editor:
Shellfish allergy (SA) is a leading cause of food-induced
anaphylaxis1 and the most common cause of adult-onset
food allergy, with 1-3% of the United States (US) population
affected.2-4. Nearly half (45%) of US adults with SA
report utilizing emergency services for SA symptoms over their
lifetime,2 remaining at-risk for lethal allergic
reactions. Several allergenic proteins have been identified across
shellfish species, including tropomyosin (TM), arginine kinase (AK),
myosin light chain (MLC), sarcoplasmic calcium binding protein (SCP),
hemocyanin, troponin C, and triosephosphate
isomerase.5 The allergens of major importance in SA
are the muscle proteins TM and AK. TM, the major allergen with
specific-IgE antibodies in < 90% of SA patients, is
associated with severe clinical reactivity. AK is a pan-allergen with
cross-reactivity with crustaceans and cephalopods.5
Cross-reactivity has been observed clinically when SA patients ingest
various invertebrate species with subsequent allergic reactions, but
further study of shrimp sIgE-binding between different shrimp species is
needed.6,7 This study examined the sIgE-binding
patterns to 2 shrimp species from the Gulf of Mexico and Southeast Asia
in US SA patients.
SA patients with shrimp-induced allergic reactions and positive
immediate skin prick testing (IHST) and/or shrimp sIgE
ImmunoCAP™ levels were recruited from the Baylor
College of Medicine (BCM) Allergy and Immunology Clinics. The study was
approved by the BCM IRB and all participants provided written, informed
consent. The patients underwent IHST to shrimp extract (mixture ofPenaeus borealis , Penaeus monodon, Metapenaeus barbata and
Metapenaeopsis joyner) , raw shrimp, cooked shrimp,Dermatophagoides pteronyssinus (Der p1, Der p 10) ,Dermatophagoides farinae (Der f1) , cockroach, codfish, crab,
lobster, and oyster using extracts from Greer™.
ImmunoCAP™ ISAC™ testing
(ThermoFisher™) assessed total IgE as well as sIgE
levels for shrimp, recombinant Penaeus aztecus (TM), Der
p10 , Der p1 , Der p2 , recombinant Penaeus monodonAK, MLC, SCP, troponin C, crab, lobster, cockroach, clam, and oyster.
Western blot (WB) analysis of sIgE-binding profile to the major
allergenic proteins TM, AK, MLC, and SCP in Penaeus aztecus(Brown shrimp) and P monodon (Black tiger shrimp) was
performed.
Fifteen SA patients between the ages of 2-17 years were enrolled.(Table
1) The most frequent symptoms were urticaria and angioedema.
Forty-percent had antihistamine treatment, one required steroids, and
none required epinephrine or albuterol. When examining sIgE-binding
patterns to the major allergens, WB revealed nearly identical
sIgE-binding profiles to tropomyosin, MLC and SCP in both species in the
heated shrimp extracts.(Figure 1.) Eight subjects (53%) demonstrated
sIgE-binding to TM and six to SCP (40%). There was variability in the
binding to other shrimp proteins, particularly in the unheated
shrimp.5 The proposed sIgE-binding allergens have been
identified by molecular weight,5,6 but need to be
confirmed in future molecular studies.
The presence of Southeast Asian Black tiger shrimp sIgE has been
established and quantified through ImmunoCAP™ISAC™ testing, with over 50% of patients having
binding to TM, 33% to SCP, 27% to AK and 13% each to MLC and troponin
C.6 Nevertheless, each individual patient’s binding
pattern in our study was similar between the two species, both unheated
(Fig 1A,B) and heated proteins (Fig 1C,D). These similar sIgE-binding
patterns to the major allergens suggested conservation of the epitopes
between different species of shrimp.
According to the Food and Agricultural Organization of the United
Nations, Penaeus aztecus is native to the north-western Atlantic
Ocean and Gulf of Mexico, while Penaeus monodon is native to the
coasts of Southeast Asia, South Asia, East Africa, and Australia. Our
study demonstrates shared epitopes among the major shrimp proteins for
Gulf Brown shrimp and Southeast Asian Black tiger shrimp in US shrimp
allergic subjects, implicating shared diagnostic and therapeutic
potential for SA to varied shrimp species.