Allergy
CORRESPONDENCE
Peanut anaphylaxis: the usefulness of molecular-based allergy diagnostics DOI:10.1111/all.12527
The peanut is the fruit of the herbaceous plant Arachis hypogea belonging to the Fabaceae (leguminous) family. The fruit (peanut) arises as a leguminous growing underground (hypogea), containing 2–3 seeds, commonly eaten roasted or worked to obtain oil or butter. The peanut allergy (PA) prevalence is about 1–2% in children, and PA may account also for severe food allergy (1). The severity of reactions may depend on the type of allergen component sensitization. In this regard, at least 11 peanut allergen proteins have been identified and characterized (2– 4). Ara h 1, 2 and 3 are the major peanut allergens belonging to the seed storage proteins family (Ara h 1 is a vicilin, Ara h 2 is a conglutin, Ara h 3 is a glycinin). Ara h 4 is a glycinin; Ara h 5 is a profilin. Ara h 6 and 7 are similar to Ara h 2. Ara h 8 is a PR-10 protein. Ara h 9 is a lipid transfer protein (LTP). Ara h 10 and 11 are oleosins. However, Ara h 2 is the most important peanut allergen component and positivity to Ara h 2 defines a ‘true’ PA (2). The PA diagnostic work-up is based on history, detection of allergen-specific IgE by skin prick test and/or serum assessment, and oral challenge. The raw allergen extract is available since much time. However, molecular-based allergy diagnostics allows to define and to characterize the sensitiza-
tion profile, so identifying potential dangerous proteins and suggesting a more precise prognosis and improving the management. Very recently, Klemans et al. (5) reported that the diagnostic value of sIgE to Ara h 6 on adults was as good as to Ara h 2 PA. However, reported anaphylaxis was not considered in that study. Therefore, the aim of this study was to compare children with peanut anaphylaxis to children with less severe PA investigating the role of molecular-based allergy diagnostics. We retrospectively considered 14 children with history of peanut anaphylaxis and 15 children with diagnosed PA. Specific IgE to raw peanut allergen was measured by ImmunoCAP method (Thermo Fisher, Milan, Italy). Specific IgE to molecular components of peanut, such as Ara h 1, Ara h 2, Ara h 3, Ara h 6, Ara h 8 and Ara h 9, was assayed by the semiquantitative ISAC method (Thermo Fisher). Allergen-specific IgE levels to raw peanut were significantly higher in the anaphylaxis group (P = 0.0044) (Table 1). Sensitization to either Ara h 2 or Ara h 3 was more frequently detected in the anaphylaxis group (P = 0.0209 and P = 0.0007, respectively). Receiver operating characteristic analysis showed that raw peanut cut-off > 2.1 kUA/l, Ara h
Table 1. Demographic and clinical characteristics of the studied subjects
Age at visit [year, mean (SD)] Male gender [No of subjects (%)] Total IgE (kU/l) Specific IgE to raw peanut (kUA/l) Positive pts to specific IgE (>0.35 kUA/l) Specific Ige to Ara h 1 (ISU-E) Positive pts. to Ara h 1 (≥0.3 ISU-E) [No Specific Ige to Ara h 2 (ISU-E) Positive pts. to Ara h 2 (≥0.3 ISU-E) [No Ara h 3 levels (ISU-E) Positive pts. to Ara h 3 (≥0.3 ISU-E) [No Specific Ige to Ara h 6 (ISU-E) Positive pts. to Ara h 6 (≥0.3 ISU-E) [No Specific Ige to Ara h 8 (ISU-E) Positive pts. to Ara h 8 (≥0.3 ISU-E) [No Specific Ige to Ara h 9 (ISU-E) Positive pts. to Ara h 9 (≥0.3 ISU-E) [No
[No of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)]
Peanut anaphylaxis (N = 14)
Peanut allergy (N = 15)
P#
8.32 10 890.50 24.15 14 0.29 7 0.29 8 0.29 8 0.29 1 0.29 6 0.29 1
8.21 11 809.00 1.63 14 0.29 3 0.29 2 0.29 0 0.29 3 0.29 7 0.29 1
0.11* 1.00† 0.42 0.0044 1.00† 0.09 0.13† 0.0178 0.0209† 0.0079 0.0007† 0.62 0.60† 0.75 0.84§ 0.98 1.00†
(4.60) (71.43) (627.50–480.50) (4.71–88.60) (100) (0.29–8.00) (50.00) (0.29–20.00) (57.14) (0.29–5.10) (57.14) (0.29–0.29) (7.14) (0.29–2.00) (42.86) (0.29–0.29) (7.14)
(2.96) (73.33) (257.00–1105.00) (1.00–3.50) (93.3) (0.29–0.29) (20.00) (0.29–0.29) (13.33) (0.29–0.29) (0.29–0.29) (20.00) (0.29–1.30) (46.67) (0.29–0.29) (6.67)
SD, standard deviation; ISU-E, ISAC Standardized Units. Unless otherwise specified, all data are reported as median with lower and upper quartiles in parentheses; #P values refer to the Mann–Whitney U-test unless otherwise specified; *P value refers to the unpaired t-test; §P value refers to the chi-square test; †P value refers to the Fisher exact test.
Allergy 70 (2015) 129–130 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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Correspondence
Table 2. Sensitivity, specificity, positive and negative predictive values for each test used to predict anaphylaxis
Total IgE levels (kU/l) Raw peanut levels (kUA/l) Ara h 1 levels (ISU-E) Ara h 2 levels (ISU-E) Ara h 3 levels (ISU-E) Ara h 8 levels (ISU-E) Ara h 9 levels (ISU-E)
Cut-off
AUC (IC95%)
Sensitivity %
Specificity %
PPV
NPV
358.00 2.09 1.00 4.70 0.29 1.30 0.60
0.625 0.850 0.686 0.757 0.786 0.538 0.505
100.00 90.00 50.00 57.10 57.10 42.90 7.10
44.40 75.00 93.30 100.00 100.00 80.00 100.00
61.54 75.00 87.50 100.00 100.00 66.67 100.00
80.00 90.00 66.67 71.43 71.43 60.00 53.57
(0.363–0.842) (0.634–0.963) (0.488–0.844) (0.563–0.896) (0.594–0.915) (0.344–0.724) (0.314–0.694)
Cut-off values were determined by means of the ROC curve analysis.
1 cut-off > 1 ISU, Ara h 2 cut-off > 4.7 ISU and positivity for Ara h 3 had fair reliability to predict anaphylaxis being area under the curve 0.85, 0.69, 0.76 and 0.79, respectively (Table 2). However, only 1 child of anaphylaxis group and 3 PA ones were positive to Ara h 6. These findings support the concept that both traditional specific IgE assay and microarray could be useful and should be integrated for an optimal diagnosis. Therefore, we believe that molecular-based allergy diagnostic should be performed in children with PA, mainly with anaphylaxis, for better defining the sensitization profile and improve the prognosis and the management of PA children. On the other hand, Ara h 6 seems to be scarcely relevant in paediatric population. In conclusion, high levels of IgE to raw peanut and positivity to Ara h 1, 2 and 3, mainly if multiple, may be considered marker of severe HA, and adequate counselling should be adopted.
Conflicts of interest The authors declare that they have no conflicts of interest. Author contributions All authors contributed to the paper. G. Ciprandi1, A. Pistorio2, M. Silvestri3, G. A. Rossi3, and M. A. Tosca3 1 Medicine Department, IRCCS – Azienda Ospedaliera Universitaria San Martino, 2 Epidemiology and Biostatistics Service, Istituto Giannina Gaslini, 3 Pulmonary Disease and Allergy Unit, Istituto Giannina Gaslini, Genoa, Italy E-mail: [email protected]
Funding Partially funded by Ricerca Corrente – Italian Ministry of Health. References 1. Tariq SM, Stevens M, Matthews S, Ridout S, Twiselton R, Hide DW. Cohort study of peanut and tree nut sensitisation by age of 4 years. BMJ 1996;313: 514–517. 2. Klemans RJ, Otte D, Knol M, Knol EF, Meijer Y, Gmelig-Meyling FH et al. The diagnostic value of specific IgE to Ara h 2 to predict peanut allergy in children is comparable to a validated and updated diagnostic
130
prediction model. J Allergy Clin Immunol 2013;131:157–163. 3. Asarnoj A, Moverare R, Ostblom E, Poorafshar M, Lilja G, Hedlin G et al. IgE to peanut allergen components: relation to peanut symptoms and pollen sensitization in 8-yearolds. Allergy 2010;65:1189–1195. 4. Lauer I, Dueringer N, Pokoj S, Rehm S, Zoccatelli G, Reese G et al. The non-specific lipid transfer protein, Ara h 9, is an important
allergen in peanut. Clin Exp Allergy 2009;39:1427–1437. 5. Klemans RJB, Knol EF, Bruijnzeel-Koomen CAFM, Knulst AC. The diagnostic accuracy of specific IgE to Ara h 6 in adults is as good as Ara h 2. Allergy 2014;69:1112– 1114.
Allergy 70 (2015) 129–130 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
CORRESPONDENCE
Peanut anaphylaxis: the usefulness of molecular-based allergy diagnostics DOI:10.1111/all.12527
The peanut is the fruit of the herbaceous plant Arachis hypogea belonging to the Fabaceae (leguminous) family. The fruit (peanut) arises as a leguminous growing underground (hypogea), containing 2–3 seeds, commonly eaten roasted or worked to obtain oil or butter. The peanut allergy (PA) prevalence is about 1–2% in children, and PA may account also for severe food allergy (1). The severity of reactions may depend on the type of allergen component sensitization. In this regard, at least 11 peanut allergen proteins have been identified and characterized (2– 4). Ara h 1, 2 and 3 are the major peanut allergens belonging to the seed storage proteins family (Ara h 1 is a vicilin, Ara h 2 is a conglutin, Ara h 3 is a glycinin). Ara h 4 is a glycinin; Ara h 5 is a profilin. Ara h 6 and 7 are similar to Ara h 2. Ara h 8 is a PR-10 protein. Ara h 9 is a lipid transfer protein (LTP). Ara h 10 and 11 are oleosins. However, Ara h 2 is the most important peanut allergen component and positivity to Ara h 2 defines a ‘true’ PA (2). The PA diagnostic work-up is based on history, detection of allergen-specific IgE by skin prick test and/or serum assessment, and oral challenge. The raw allergen extract is available since much time. However, molecular-based allergy diagnostics allows to define and to characterize the sensitiza-
tion profile, so identifying potential dangerous proteins and suggesting a more precise prognosis and improving the management. Very recently, Klemans et al. (5) reported that the diagnostic value of sIgE to Ara h 6 on adults was as good as to Ara h 2 PA. However, reported anaphylaxis was not considered in that study. Therefore, the aim of this study was to compare children with peanut anaphylaxis to children with less severe PA investigating the role of molecular-based allergy diagnostics. We retrospectively considered 14 children with history of peanut anaphylaxis and 15 children with diagnosed PA. Specific IgE to raw peanut allergen was measured by ImmunoCAP method (Thermo Fisher, Milan, Italy). Specific IgE to molecular components of peanut, such as Ara h 1, Ara h 2, Ara h 3, Ara h 6, Ara h 8 and Ara h 9, was assayed by the semiquantitative ISAC method (Thermo Fisher). Allergen-specific IgE levels to raw peanut were significantly higher in the anaphylaxis group (P = 0.0044) (Table 1). Sensitization to either Ara h 2 or Ara h 3 was more frequently detected in the anaphylaxis group (P = 0.0209 and P = 0.0007, respectively). Receiver operating characteristic analysis showed that raw peanut cut-off > 2.1 kUA/l, Ara h
Table 1. Demographic and clinical characteristics of the studied subjects
Age at visit [year, mean (SD)] Male gender [No of subjects (%)] Total IgE (kU/l) Specific IgE to raw peanut (kUA/l) Positive pts to specific IgE (>0.35 kUA/l) Specific Ige to Ara h 1 (ISU-E) Positive pts. to Ara h 1 (≥0.3 ISU-E) [No Specific Ige to Ara h 2 (ISU-E) Positive pts. to Ara h 2 (≥0.3 ISU-E) [No Ara h 3 levels (ISU-E) Positive pts. to Ara h 3 (≥0.3 ISU-E) [No Specific Ige to Ara h 6 (ISU-E) Positive pts. to Ara h 6 (≥0.3 ISU-E) [No Specific Ige to Ara h 8 (ISU-E) Positive pts. to Ara h 8 (≥0.3 ISU-E) [No Specific Ige to Ara h 9 (ISU-E) Positive pts. to Ara h 9 (≥0.3 ISU-E) [No
[No of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)] of subjects (%)]
Peanut anaphylaxis (N = 14)
Peanut allergy (N = 15)
P#
8.32 10 890.50 24.15 14 0.29 7 0.29 8 0.29 8 0.29 1 0.29 6 0.29 1
8.21 11 809.00 1.63 14 0.29 3 0.29 2 0.29 0 0.29 3 0.29 7 0.29 1
0.11* 1.00† 0.42 0.0044 1.00† 0.09 0.13† 0.0178 0.0209† 0.0079 0.0007† 0.62 0.60† 0.75 0.84§ 0.98 1.00†
(4.60) (71.43) (627.50–480.50) (4.71–88.60) (100) (0.29–8.00) (50.00) (0.29–20.00) (57.14) (0.29–5.10) (57.14) (0.29–0.29) (7.14) (0.29–2.00) (42.86) (0.29–0.29) (7.14)
(2.96) (73.33) (257.00–1105.00) (1.00–3.50) (93.3) (0.29–0.29) (20.00) (0.29–0.29) (13.33) (0.29–0.29) (0.29–0.29) (20.00) (0.29–1.30) (46.67) (0.29–0.29) (6.67)
SD, standard deviation; ISU-E, ISAC Standardized Units. Unless otherwise specified, all data are reported as median with lower and upper quartiles in parentheses; #P values refer to the Mann–Whitney U-test unless otherwise specified; *P value refers to the unpaired t-test; §P value refers to the chi-square test; †P value refers to the Fisher exact test.
Allergy 70 (2015) 129–130 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
129
Correspondence
Table 2. Sensitivity, specificity, positive and negative predictive values for each test used to predict anaphylaxis
Total IgE levels (kU/l) Raw peanut levels (kUA/l) Ara h 1 levels (ISU-E) Ara h 2 levels (ISU-E) Ara h 3 levels (ISU-E) Ara h 8 levels (ISU-E) Ara h 9 levels (ISU-E)
Cut-off
AUC (IC95%)
Sensitivity %
Specificity %
PPV
NPV
358.00 2.09 1.00 4.70 0.29 1.30 0.60
0.625 0.850 0.686 0.757 0.786 0.538 0.505
100.00 90.00 50.00 57.10 57.10 42.90 7.10
44.40 75.00 93.30 100.00 100.00 80.00 100.00
61.54 75.00 87.50 100.00 100.00 66.67 100.00
80.00 90.00 66.67 71.43 71.43 60.00 53.57
(0.363–0.842) (0.634–0.963) (0.488–0.844) (0.563–0.896) (0.594–0.915) (0.344–0.724) (0.314–0.694)
Cut-off values were determined by means of the ROC curve analysis.
1 cut-off > 1 ISU, Ara h 2 cut-off > 4.7 ISU and positivity for Ara h 3 had fair reliability to predict anaphylaxis being area under the curve 0.85, 0.69, 0.76 and 0.79, respectively (Table 2). However, only 1 child of anaphylaxis group and 3 PA ones were positive to Ara h 6. These findings support the concept that both traditional specific IgE assay and microarray could be useful and should be integrated for an optimal diagnosis. Therefore, we believe that molecular-based allergy diagnostic should be performed in children with PA, mainly with anaphylaxis, for better defining the sensitization profile and improve the prognosis and the management of PA children. On the other hand, Ara h 6 seems to be scarcely relevant in paediatric population. In conclusion, high levels of IgE to raw peanut and positivity to Ara h 1, 2 and 3, mainly if multiple, may be considered marker of severe HA, and adequate counselling should be adopted.
Conflicts of interest The authors declare that they have no conflicts of interest. Author contributions All authors contributed to the paper. G. Ciprandi1, A. Pistorio2, M. Silvestri3, G. A. Rossi3, and M. A. Tosca3 1 Medicine Department, IRCCS – Azienda Ospedaliera Universitaria San Martino, 2 Epidemiology and Biostatistics Service, Istituto Giannina Gaslini, 3 Pulmonary Disease and Allergy Unit, Istituto Giannina Gaslini, Genoa, Italy E-mail: [email protected]
Funding Partially funded by Ricerca Corrente – Italian Ministry of Health. References 1. Tariq SM, Stevens M, Matthews S, Ridout S, Twiselton R, Hide DW. Cohort study of peanut and tree nut sensitisation by age of 4 years. BMJ 1996;313: 514–517. 2. Klemans RJ, Otte D, Knol M, Knol EF, Meijer Y, Gmelig-Meyling FH et al. The diagnostic value of specific IgE to Ara h 2 to predict peanut allergy in children is comparable to a validated and updated diagnostic
130
prediction model. J Allergy Clin Immunol 2013;131:157–163. 3. Asarnoj A, Moverare R, Ostblom E, Poorafshar M, Lilja G, Hedlin G et al. IgE to peanut allergen components: relation to peanut symptoms and pollen sensitization in 8-yearolds. Allergy 2010;65:1189–1195. 4. Lauer I, Dueringer N, Pokoj S, Rehm S, Zoccatelli G, Reese G et al. The non-specific lipid transfer protein, Ara h 9, is an important
allergen in peanut. Clin Exp Allergy 2009;39:1427–1437. 5. Klemans RJB, Knol EF, Bruijnzeel-Koomen CAFM, Knulst AC. The diagnostic accuracy of specific IgE to Ara h 6 in adults is as good as Ara h 2. Allergy 2014;69:1112– 1114.
Allergy 70 (2015) 129–130 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
