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J Investig Allergol Clin Immunol 2019; Vol. 29(5): 378-398 © 2019 Esmon Publicidad
Selective Allergy to Conger Fish due to Parvalbumin
Argiz L1, Vega F1, Castillo M2, Pineda F2, Blanco C1,3
1Department of Allergy, Hospital Universitario de La Princesa,
Instituto de Investigación Sanitaria Princesa (IP), Madrid, Spain
2Application Laboratory, Diater Laboratories, Madrid, Spain
3RETIC ARADYAL RD16/0006/0015, Instituto de Salud Carlos
III, Madrid, Spain
J Investig Allergol Clin Immunol 2019; Vol. 29(5): 390-391
doi: 10.18176/jiaci.0412
Key words: Conger fish. Selective allergy. Parvalbumin. Fish allergy.
Food allergy.
Palabras clave: Congrio. Parvalbúmina. Alergia selectiva. Alergia a
pescado. Alergia alimentaria.
Fish is one of the most frequent causes of food allergy,
affecting up to 0.3% of the world’s population [1]. Most
fish-allergic patients show marked clinically relevant cross-
reactivity, while a minority of patients experience selective
allergy to specific fish species, with good tolerance to other
fish families [2].
We report the case of a 32-year-old woman with mild
rhinoconjunctivitis due to pollens and animal dander. In 2017,
she developed generalized urticaria, cough, oral pruritus,
dysphagia, and abdominal pain immediately after ingestion
of a small piece of fideuá, a typical Spanish dish made with
noodles, prawns, squid, and fish, which in this case was conger,
although hake or snuff are more frequently used. Conger
belongs to the subclass Actinopterygii, order Anguilliformes,
which also includes eel and moray. Broth made from the head,
thorns, and skin of fish is used as water for cooking fideuá.
The patient’s condition improved hours after symptomatic
treatment in the emergency department. She subsequently
tolerated pasta and several other types of fish (eg, hake,
monkfish, cod, sardine, tuna, salmon, and swordfish).
The allergy work-up included the following (see
Supplementary Material):
– Skin prick-tests with commercial extracts and prick-by-
prick tests with foods, which yielded positive prick-by-
prick results to both raw conger body (12×11 mm) and
cooked conger body (10×9 mm).
– Serum specific IgE (kUA/L) using ImmunoCAP, which
yielded positive results to eel (0.81), hake (0.74),
rooster (0.5), carp parvalbumin (rCyp c 1) (0.7), and
cod parvalbumin (rGad c 1) (0.65) and negative results
to cod, salmon, sole, sardine, and anchovy.
Good tolerance to prawns and squid was also confirmed.
The patient was diagnosed with anaphylaxis due to conger
allergy, and a conger-free diet was recommended.
SDS-PAGEwas performed under reducing and nonreducing
conditions (Supplementary Material). No relevant differences
between both conditions were revealed, suggesting that the
proteins involved were mainly monomeric proteins.
Immunoblotting with the patient's serum and the above-
mentioned extracts (Figure) showed that IgE recognized
multiple bands, including the following:
1. A 40-50–kDa band, which was detected in raw conger
and in all other tested raw fish extracts, but not in cooked
conger.
2. A 12-kDa band, which was detected only in raw and
cooked conger, but was absent in all other fish tested.
3. A 18-kDa band, which was detected only in the conger
eye extract.
The eye of the conger is the part of the head used for
making the broth of fideuá. This band was not further studied,
because fish eyes are not eaten in Spain and the patient had
not experienced problems with broth from other types of fish.
Immunoblotting-inhibition was performed with carp and
conger extracts under reducing and nonreducing conditions,
and the patient’s serum was preincubated with conger
extract. As a result, IgE no longer recognized the proteins in
the extracts, thus indicating that primary sensitization was
probably due to conger. Disappearance of the 40-50–kDa
bands suggests that these proteins were similar in both extracts.
Peptide mass fingerprinting was performed with conger
extract using spectrometry to characterize the 12-kDa band,
since this was thought to have induced the patient’s reaction.
The band was both conger-specific and thermoresistant. The
4 most relevant peptides were selected after a process of
enzymatic digestion, and a specific search for the MASCOT
peptide sequence combining MS (proteins) and MSMS
(peptides) was performed in NCBI Chordata. The only
match found was for an 11–amino acid peptide with the
ß-parvalbumin of the fish Scleropages formosus in 1 of the 4
peptides (Supplementary Figure). This 11–amino acid peptide
has a homology of >80% with many other fish parvalbumins.
Reducing Conditions
1
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16
5
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75
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37
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25
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Molecular Weight
Molecular Weight
Nonreducing Conditions
Figure. IgE-immunodetection performed with the patient’s serum and
the following extracts: Lane 1, Eel; 2, Eel skin; 3, Conger head; 4, Conger
body; 5, Conger bone; 6, Conger eye; 7, Conger skin; 8, Salmon; 9,
Anisakis; 10, Tuna; 11, Cod; 12, Carp; 13, Sole; 14, Hake; 15, Sardine;
16, Cooked conger.
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