Differential sensitization patterns to fish allergens between populations
To understand the IgE sensitization pattern, we purified the well-characterized fish allergens including collagen, β-enolase, aldolase and β-parvalbumin from both salmon and grass carp. All allergens had >90% purity as validated by SDS-PAGE (Figures 2A & B). IgE binding to these allergens coated onto ELISA plates was evaluated using 46 serum samples from each of HK and Japan subjects. The respective sensitization rates are summarized in Table 2.
For both fishes, parvalbumin was the major allergen that showed an overall sensitization rate of 74.7% (71/95) in fish allergic subjects (Figures 2C-F) while enolase is the least common allergen (17.8% sensitization). Interestingly, the sensitization rates to salmon enolase and aldolase, the heat-labile allergens, were higher among subjects from Japan (15.2% and 23.9% respectively) than HK (4.3% and 15.2% respectively). On the other hand, the sensitization rates to salmon and grass carp collagen were higher among subjects from HK (43.5% and 30.4% respectively) than Japan (30.4% and 17.8% respectively). No remarkable difference in parvalbumin sensitization rate could be found between the two study cohorts. Mono-sensitization to salmon or grass carp parvalbumin was the most common in both populations (28.3% to 37.0%). Only 7/96 subjects did not show IgE binding to parvalbumin but other fish allergen, and collagen represented the leading sensitizer in these patients (6/7 patients reacted to collagen). IgE-binding to both parvalbumin and collagen was the most common form of co-sensitization (13.0% to 23.9%).
For both populations, the sensitization rates to grass carp parvalbumin (68.9% for Japan and 78.3% for HK) were higher than that to salmon parvalbumin (63.0% and 56.4%) (Table 2). The IgE avidity (i.e. OD450nm) of grass carp parvalbumin was also higher than salmon parvalbumin as noted in the heatmap (Figure 2). Despite of the significantly higher salmon-sIgE level than grass carp-sIgE level, IgE avidity to grass carp parvalbumin was significantly higher than that to salmon parvalbumin among the Japanese fish allergic subjects (Wilcoxon matched-pairs signed rank test, p < 0.0001). However, no difference could be detected for grass carp parvalbumin binding intensity between the two populations regardless of the significantly higher grass carp-sIgE level for the HK subjects. In contrast, both the sensitization rates and IgE avidity of salmon collagen were higher than those of grass carp collagens.
Analyses of specific sensitization were summarized in Table 3. Out of the 36 HK subjects with positive grass carp parvalbumin-specific IgE, ten were sensitized to grass carp parvalbumin only giving a monosensitization rate to grass carp at 27.8%. On the contrary, none with positive salmon parvalbumin-specific IgE (n = 26) showed IgE binding to salmon parvalbumin only. When taking both populations into consideration, the overall rate of mono-sensitization to grass carp parvalbumin (20.9%) was higher than that to salmon parvalbumin (5.5%). On the contrary, mono-sensitization to salmon collagen (44.1%) was remarkably more common than to grass carp collagen (9.1%). The two fish species did not differ with respect to sensitization rate, IgE avidity and rate of mono-sensitization to enolase and aldolase.