The low allergenicity of ray parvalbumin is confirmed in a multinational study of fish allergy
sIgE to each PV for all 263 patients was first quantified (Figure 1A ). The lowest median sIgE was observed for ray alpha-PV followed by sole and cod beta-PVs. The highest values were found for mackerel and tuna PVs (>10 kUA/L). A comparison of IgE levels to PVs from different species demonstrated statistically significant differences for most pairs (Table SIII) . In total, IgE of only 22% of the patients recognized ray PV, while for bony fish beta-PVs sensitization was observed for between 75% (sole) and 92% (tuna) of patients (Figure 1B ).
The pairwise correlation of the PV-sIgE levels showed a weak correlation between ray and any other PV (Spearman correlation coefficient ≤0.42) (Figure 1C ), while the correlations between values for beta-PV pairs were strong. The correlations were statistically significant for all PV pairs (data not shown). To further support these results, the principal component analysis (PCA) was applied to the PV-sIgE levels. PC1 and PC2 explained approximately 82.0% and 8.6% of the variance contained in the PV data, respectively (Figure S4 ). All PV-sIgE scores except for ray showed a strong correlation with PC1 while correlating weakly with PC2. Conversely, ray PV-sIgE correlated strongly with PC2. The probability of IgE test to be positive for one PV if positive for another was also determined (Figure S5 ). A positive test for any beta-PV indicated >80% probability of positivity to other beta PVs.
Next, the median IgE levels to each PV in each country were determined, and the highest were observed for the Norwegian cohort, while ray PV demonstrated lower IgE than any other in each country (Figure 1D ). To analyze whether the evolutionary distance among the PVs may be related to their different IgE levels, their sequences were aligned (Figure S6A ) and a neighbor-joining phylogenetic tree was computed (Figure S6B ). Interestingly, not only ray alpha-PV, but also sole beta-PV clustered separately from the others.