Comparison of Parvalbumin Reactivity and Levels in Different
Fishes
Considering the strong correlation between fish extract-sIgE and
parvalbumin-sIgE levels, we next examined if such allergenicity
differences in fishes are attributed by (1) differences in IgE binding
capacity of different fish parvalbumins, or (2) differences in
parvalbumin levels in different fishes. Firstly, 37 serum samples from
the sensitized group were assayed for IgE reactivity against purified
recombinant parvalbumins from tuna, salmon (β-1 and β-2), cod, grouper,
catfish, grass carp and tilapia (Fig 3A). Our data showed that IgE
binding did not increase along the allergenicity ladder (Fig 3B). No
statistical difference was detected among the tested parvalbumins even
when comparing between tuna and tilapia, despite an 11-fold lower
tuna-sIgE than tilapia-sIgE. Interestingly, salmon parvalbumin β-1 had
remarkably lower IgE binding comparing to all parvalbumins except for
tuna parvalbumin while grass carp parvalbumin had significantly stronger
IgE binding than parvalbumins from tuna, salmon β-1, cod and tilapia.
These results suggested that the difference in allergenicity is not due
to IgE binding capacity of parvalbumins.
We next compared parvalbumin levels in the extracted fish protein by
SDS-PAGE and densitometry analysis. Parvalbumin appeared as a 9-12 kDa
protein in all fish extracts, while two parvalbumin isoforms could be
visualized in halibut, grass carp and tilapia (Fig 3C). With reference
to salmon parvalbumin (relative intensity = 1), the relative parvalbumin
content showed no statistical difference among tuna, halibut and salmon,
as well as among catfish, grass carp and tilapia (Fig 3D). Parvalbumin
content was significantly higher in cod comparing to salmon, halibut,
and tuna, as well as in grouper comparing to cod. It is noted that
parvalbumin levels in catfish, grass carp (isoform 2), and tilapia
(isoform 2) were significantly higher than that in all other tested
fishes. Importantly, the relative levels of parvalbumin positively
correlated with the sIgE reactivity of the respective fish (r = 0.925, p
=.001) and incident of self-reported allergic reactions (r = 0.89, p
=.004). We also further validated the expression of parvalbumins by a
transcriptomic approach. The transcriptomic expression level of these
parvalbumins was similar to the results from protein-based analysis (Fig
3E). Yet, it is noted that the expression of GAPDH and aldolase were
remarkably higher in halibut, yellowfin tuna and salmon comparing to the
freshwater fishes, cod and grouper. These results suggested that the
difference in allergenicity is due to the amount of parvalbumin in fish
muscle.