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Clinical and Diagnostic Laboratory Immunology, March 2003, p. 229-232, Vol. 10, No. 2
1071-412X/03/$08.00+0 DOI: 10.1128/CDLI.10.2.229-232.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Detection of Cross-Reactivity for Atopic Immunoglobulin E against Multiple Allergens
Yee-Hsuan Chiou,1 Chung-Yee Yuo,2 Lin-Yu Wang,3 and Shiao-ping Huang3*
Department of Pediatrics, Kaohsiung Veterans General Hospital and National Yang-Ming University,1
Department of Biology, Kaohsiung Medical University,2
Department of Medical Technology, Fooyin University, Ta-Liao Hsiang, Kaohsiung Hsien, Taiwan, Republic of China3
Received 29 August 2002/
Returned for modification 4 September 2002/
Accepted 5 December 2002

ABSTRACT
The existence of specific immunoglobulin E (IgE) allows us to
determine the allergens that cause the allergic disease. For
the purposes of allergen avoidance and immunotherapy, the measurement
of specific IgE is widely applied in clinical laboratories.
However, if IgE from the serum of an allergic patient exhibits
reactivity to multiple allergens, it would cause a problem.
The present study analyzes whether the serum IgE with multiple
reactivity is due to the presence of unique IgE against the
common epitope shared by different allergens or the presence
of multiple IgEs against different epitopes on different allergens.
The quantitative-competitive inhibition tests and the immunoblotting
were applied to analyze the immunosimilarity among examined
allergens. The result shows that the competitive inhibition
of IgE binding between shrimp and crab allergens is higher than
those between either shrimp and cockroach or between crab and
cockroach. Furthermore, the results of immunoblotting are consistent
with those of quantitative-competitive inhibition tests. These
results allow us to detect the cross-reactivity for atopic IgE
against multiple allergens.

INTRODUCTION
Atopic allergy, the most widespread immunologic disorder in
human, is characterized by the increased and persistent level
of immunoglobulin E (IgE) in serum (
4,
11,
18). Family and twin
studies have shown that both genetic and environmental factors
are involved in the atopic reaction (
14,
20). To avoid the allergen
from environment exactly, the allergen for an atopic individual
should be identified by the measurement of the specific IgE
in serum with suspicious allergens. In particular, the cross-reactivity
among allergens has been documented (
1). Many species of grass
pollen, latex, and fruit allergens share their immunological
similarities with glycoprotein (
2,
7-
9,
16,
21). In addition,
the tropomyosin in cockroach was identified as a major allergen
with potential cross-reactivity with mite and shrimp allergens
(
12,
13,
19). Calcium-involved carbohydrate-containing IgE epitopes
also play a role in the cross-reactivity among several species
of fish (
3,
10). Furthermore, the investigation of atopic infants
revealed that human milk whey protein and cow milk ß-lactoglobulin
not only share the epitope for IgE binding in vitro but also
cause the atopic reaction in vivo (
5). Since the serum IgE with
the reactivity to multiple allergens is commonly seen in clinical
patients (
6), we wanted to characterize the immunosimilarity
among allergens. First, the atopic sera with the multiple IgE
reactivity to cockroach, crab, and shrimp were chosen for the
analysis of cross-reactivity with quantitative-competitive inhibition
tests. As a control, other atopic sera with multiple IgE reactivities
to dust mites, house dust, and dog dander were also examined
for the immunosimilarity by quantitative-competitive inhibition
tests. Then, the sera with cross-reactivity were further analyzed
by immunoblotting. The results allow us to understand the prevalence
of immunosimilarity among examined allergens.

MATERIALS AND METHODS
Study populations.
The serum samples of atopic individuals with elevated specific
IgE reactive to multiple allergens were collected from the Department
of Pediatrics, Kaohsiung Veterans General Hospital. The results
of specific IgE, examined by using a MAST CLA allergen-specific
IgE assay (Hitachi Chemical Diagnostics, Inc.), were used for
screening and selection of patients. From 36 allergens examined,
sera with reactivity to multiple allergens, i.e., two or more
allergen items, were collected. There were 67 sera collected
for this study. After the specific IgE levels were measured,
the sera were stored as 1-ml aliquots at -20°C for further
analysis.
Quantitative examination of serum IgE.
Based on the results of MAST system, the positive allergen items were chosen for the quantitative examination of atopic sera. The quantitative examinations were performed in Pharmacia CAP-FEIA system (Pharmacia & Upjohn Diagnostics AB, Uppsala, Sweden). Generally, 50 µl of the serum was used for each measurement. If the atopic serum appeared to have a titer higher than class 6 (>100 kU/liter), a 10-fold dilution was performed.
Quantitative-competitive inhibition test.
The quantitative-competitive inhibition tests were performed by using Pharmacia CAP-FEIA system. Sera were prebound with ImmunoCAP: this allergen is the candidate with cross-reactivity to the following allergens examined. After 2 h of prebinding, the level of serum IgE was determined according to the procedure of the Pharmacia CAP-FEIA system. The percentage of the quantitative-competitive inhibition test was calculated by using the IgE reactivity with or without the prebinding of allergens as follows: percent inhibition = [(IgEO - IgEA)/IgEO] x 100, where IgEO is the IgE reactivity without pre-binding and IgEA is the IgE reactivity with prebinding with allergens.
IgE immunoblotting.
The AlaBLOT specific IgE allergen strips (Diagnostic Products Co., Los Angeles, Calif.) were used to identify the serum IgE-reactive allergens by immunochemical means. According to the procedures of the AlaBLOT specific IgE allergen strips test, the diluted serum (50 µl in 500 µl) was added onto the strip, followed by incubation for 2 h at room temperature. The strip was then washed three times and incubated with enzyme-labeled anti-IgE for 30 min. After three washes, the color of the protein bands with reaction to serum IgE was developed by adding substrate reagent. The molecular weights of the proteins were estimated according to the description in each lot of strips by using relative mobility of molecular weight markers. For the inhibition of immunoblotting, the serum was also prebound with ImmunoCAP; these allergens are cross-reactive to the examined allergen. The serum was then used for the IgE immunoblotting to determine the extent of the inhibition of immunoblotting.

RESULTS AND DISCUSSION
Immunosimilarity among allergens.
The sera examined here contained IgE antibodies to multiple
allergens. After the examination with the CAP-FEIA system, 63
sera of the 67 collected samples showed reactivity to multiple
allergens (Table
1).
Since most sera with reactivity to shrimp allergens were also
reactive to crab and cockroach allergens, 15 sera were then
chosen for the analysis of cross-reactivity among shrimp, crab,
and cockroach serum samples by the quantitative-competitive
inhibition tests. As shown in Table
2, the inhibition of the
serum IgE is an average of 34% between shrimp and cockroach,
65% between shrimp and crab, and 35% between crab and cockroach.
In particular, among the 15 examined sera, 3 showed an inhibition
of >50% between shrimp and cockroach sera, 11 showed a inhibition
of >50% between shrimp and crab sera, and 4 showed a inhibition
of >50% between crab and cockroach sera. Furthermore, the
inhibition between shrimp and crab sera was shown to be significant
by the chi-square test (
P < 0.01). Therefore, this result
indicated that the immunosimilarity between shrimp and crab
sera is indeed present in the serum IgE of atopic individuals.
In addition, five sera were chosen for the analysis of cross-reactivity
among dust mites, house dust, and dog dander allergens by the
quantitative-competitive inhibition tests. As shown in Table
3, small inhibitions of the serum IgE against these allergens
were observed. The result indicated that these sera appear to
have the distinct IgEs reactive to dust mites, house dust, and
dog dander separately.
The quantitative-competitive inhibition test has been applied
to examine the level of immunosimilarity between allergens.
For example, it was used by Petersen et al. for the examination
of IgE cross-reactivity between tomato fruit and grass pollen
allergens (
17) and by Hansen et al. for the examination of IgE
cross-reactivity among different species of fish (
10). The results
of quantitative-competitive inhibition tests in our study indicate
that the extent of immunosimilarity was low among dust mites,
house dust, and dog dander and higher among shrimp, crab, and
cockroach sera.
The quantitative-competitive inhibition tests in this study were performed with ImmunoCAP for prebinding of serum to allergen. The limitation of this method is that only one dose of allergen could be applied. However, we used this method to examine the cross-reactivity between two allergens in the clinical laboratory and showed that it is appropriate to analyze the cross-reactivity between two allergens.
Immunoblotting of serum IgE against shrimp, crab, and cockroach.
To examine the molecular features of cross-reactivity among shrimp, crab, and cockroach, the immunoblotting and inhibition of immunoblotting were performed. Since the result from Table 2 showed that a high degree of immunosimilarity is present between shrimp and crab and partial immunosimilarity is evident between either shrimp and cockroach or between crab and cockroach, the serum of sample 61 was chosen for this experiment. We demonstrated (Fig. 1A) that this serum exhibited reactivity to several shrimp proteins. Moreover, reactivity to shrimp proteins was dramatically inhibited if the serum was prebound with crab allergens and slightly inhibited if the serum was prebound with cockroach allergens. Figure 1B shows the immunoblotting of crab with a major reactivity to a protein of 31 kDa. In addition, the inhibition of immunoblotting is higher by shrimp allergens (lane 3) than that by cockroach allergens (lane 2). Figure 1C shows the immunoblotting of cockroach sera, and a smear of protein bands seems to indicate that many cockroach proteins were recognized by the serum IgE. In addition, the inhibition of immunoblotting with the serum prebound by either shrimp or crab allergens was consistent with the results of the quantitative-competitive inhibition tests given in Table 2. Therefore, the results of immunoblotting appear to be consistent with those of quantitative-competitive inhibition tests.
Pascual et al. have demonstrated the cross-reactivity between
IgE binding proteins from
Anisakis simplex larvae (parasite
of seafoods),
Blattella germanica (German cockroach), and
Chironomidae (red mosquito larvae) (
15). Also, Santos et al. have identified
tropomyosin as a major allergen of cockroach (
19). However,
our results show that the inhibitions between either cockroach
and shrimp or between cockroach and crab were only partial.
In particular, our examinations, including quantitative-competitive
inhibition tests and the inhibition of immunoblotting, showed
that the inhibition between shrimp and crab seems to be higher.
These results indicate that similar epitopes of shrimp and crab
allergens are involved in IgE binding. Interestingly, Cantisani
et al. also showed that the common structure of epitopes indeed
existed in human milk whey proteins and ß-lactoglobulin
in cow's milk proteins (
5). Although cross-reactivity between
epitopes in vivo may not have correlation to cross-reactivity
in a clinical setting, further studies on the peptide sequence
and tertiary structure of common epitopes should still shed
light on the molecular mechanism of IgE cross-reactivity.
In conclusion, the immunosimilarity among several allergens was quantitated with quantitative-competitive inhibition tests and analyzed based on the inhibition of immunoblotting. A high degree of immunosimilarity between shrimp and crab allergens was determined. The result indicates that the cross-reactivity between shrimp and crab sera was induced by a similar, if not identical, allergen epitope. In addition, the result of immunoblotting indicates that the 31-kDa crab protein is involved in the binding of allergen to IgE.

ACKNOWLEDGMENTS
We thank Chi-Shan Chen for the collection of serum samples.
This study was supported by grants from National Science Council, Republic of China (NSC 89-2314-B-242-005), and the Fooyin Institute of Technology (FIT-88-Med-022).

FOOTNOTES
* Corresponding author. Mailing address: Department of Medical Technology, Fooyin University, Ta-Liao Hsiang, Kaohsiung Hsien, 831, Taiwan, Republic of China. Phone: 886-7-782-7162. Fax: 886-7-782-7162. E-mail:
sphuang{at}mail.fy.edu.tw.


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Clinical and Diagnostic Laboratory Immunology, March 2003, p. 229-232, Vol. 10, No. 2
1071-412X/03/$08.00+0 DOI: 10.1128/CDLI.10.2.229-232.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.