Differential IgE binding to freshwater and seawater fishes in a Chinese population offish allergic subjects

Background: Diagnosis of fish allergy is often based on a few representative seawater fishes. We sought to compare the IgE reactivity of freshwater and seawater fishes in a Chinese population where freshwater fishes are part of traditional Chinese diet.
Method: 98 subjects with physician-diagnosed immediate-type allergic reactions to fish were recruited from five hospitals in Hong Kong. To compare the IgE reactivity of freshwater and seawater fishes, blood samples were collected from the subjects and their IgE reactivities against cod, tuna, salmon, catfish and tilapia were measured by ImmunoCAP test. To compare the IgE reactivity at a component level, IgE reactivities against the major fish allergen parvalbumin from cod (rGad c 1) and com-mon carp (rCyp c 1) were also measured by ImmunoCAP.
Results: All subjects had 0.35 kUA /L IgE against at least one of the five fishes tested by ImmunoCAP. Twenty subjects (20.4%) were sensitized to catfish and/or tilapia only with no IgE reactivity detected against any of the seawater fishes. In contrast, only one subject was sensitized to tuna and salmon without detectable IgE against fresh-water fishes. Two subjects were monosensitized to tilapia, while two other subjects were monosensitized to salmon or tuna. Among the seawater fishes, IgE reactivity is significantly lower against tuna (me-dian: 0.58 kUA /L; IQR: 0.21-1.55 kUA /L) than to cod (median: 1.14kUA /L; IQR: 0.34-3.20 kUA /L) or salmon (median: 0.87 kUA /L; IQR:0.24-3.10 kUA /L), while the two freshwater fishes catfish (median:4.19 kUA /L; IQR: 1.20 — 13.3 kUA /L) and tilapia (median: 4.69 kUA /L;IQR: 1.29 — 16.23 kUA /L) had a stronger IgE reactivity than all of the above seawater fishes. Most subjects were IgE reactive to tilapia(n = 95, 96.9%) while least subjects were IgE reactive to tuna (n = 59,60.2%). For the fish components, IgE reactivity against the common carp parvalbumin rCyp c 1 (median: 5.80 kUA /L; IQR: 1.32 — 16.1kUA /L) was significantly higher than the cod parvalbumin rGad c 1(median: 3.67 kUA /L; IQR: 0.68 — 10.4 kUA /L).
Conclusion: IgE reactivity against freshwater fishes is significantly stronger than seawater fishes in our population at both extract and component levels. Freshwater fishes should be taken into consideration for better diagnosis and clinical management of fish allergy.