Specific IgE response to purified and recombinant allergens in latex allergy
© Kurup et al; licensee BioMed Central Ltd. 2005
Received: 27 June 2005
Accepted: 10 August 2005
Published: 10 August 2005
In recent years, allergy to natural rubber latex has emerged as a major allergy among certain occupational groups and patients with underlying diseases. The sensitization and development of latex allergy has been attributed to exposure to products containing residual latex proteins. Although improved manufacturing procedures resulted in a considerable reduction of new cases, the potential risk for some patient groups is still great. In addition the prevalent cross-reactivity of latex proteins with other food allergens poses a major concern. A number of purified allergens and a few commercial kits are currently available, but no concerted effort was undertaken to evaluate them.
We studied 11 purified latex allergens, Hev b 1 to Hev b 10, and Hev b 13 along with several crude allergen extracts and two commercial ImmunoCAP assays to evaluate specific IgE antibody in the sera from latex allergic patients and controls. Health care workers and spina bifida patients with clinical symptoms of latex allergy, spina bifida patients without latex allergy, and non-atopic health care workers have been studied.
The results suggest that Hev b 2, 5, 6, and 13 together identified over 80 percent health care workers with latex allergy, while Hev b 6 along with Hev b 1 or 3 detected specific IgE antibody in all sera studied from patients with spina bifida and latex allergy. The ImmunoCAP results using both Hev b 5 amplified and non-amplified closely agreed with the clinical diagnosis of latex allergy in health care workers and in spina bifida.
Although the purified allergens and crude extracts reacted diversely with IgE from different patient groups, the results indicated that use of certain combinations of purified recombinant antigens will be useful in commercial kits or in in-house assays for detecting specific IgE antibody in the sera. The results suggest that a combination of Hev b 2, 3, 5, 6, and 13 together detected specific IgE in 80% of the sera from latex allergic patients. Both ImmunoCAPs correctly identified over 95% of latex allergic patients, however, showed reactivity with a few normal control subjects
During the 1980's and 90's, allergy to natural rubber latex had posed serious concerns, particularly in certain occupational groups exposed to latex allergens [1–4]. Among these occupational groups, health care workers (HCW) and patients with spina bifida (SB) constitute the two major populations exposed to various natural rubber latex products and have a high frequency of manifestations of latex allergy. Sensitization and the development of latex allergy have been attributed to the exposure to products containing residual latex proteins. Although considerable advances have been made in the diagnosis and patient care, no standardized tests or reagents are currently available that can be reliably and safely used in the diagnosis of latex allergy [3–5]. A crude latex extract from a clone of Malaysian rubber tree Hevea brasiliensis, clone RRIM 600 has been made available for evaluation and was proposed as a candidate allergen for skin test and in in vitro specific serum IgE assays [6, 8]. This extract has been widely tested as a skin-testing reagent and has been evaluated by the multi-center latex skin testing study task force with success, although the clone is classified as an unstable phenotype with variability in the latex composition . Crude extracts are not appropriate candidates as standardized antigens due to their variability, lack of dependability, irrelevant cross reactivity, and questionable safety in in vivo use such as skin testing. In recent years a number of genes encoding relevant antigens from natural rubber latex have been cloned and the proteins expressed . However, only a few studies have been carried out to evaluate these conventionally purified or cloned and expressed allergens . Currently, there are 13 Hevea latex allergens recognized by the IUIS Allergen Nomenclature Committee .
In recent years, several semi-automated in vitro assays have been developed commercially for detecting latex specific IgE antibody. In the present study, we investigated latex specific IgE in the sera of patients and controls using purified and crude latex allergens prepared from non-ammoniated Malaysian natural rubber latex extracts and glove extracts. The extracts were evaluated in an ELISA and the results compared with ImmunoCAP, a widely used semi-automated commercial assay for IgE antibody. The purified antigens reacted diversely with different patient sera by ELISA and no single allergen reacted with IgE from all proven latex allergic patients studied. However, Hev b 2, 5, 6, and 13 together and Hev b 6 with Hev b 1 or 3 demonstrated IgE from majority of HCW patients and spina bifida patients respectively. The ELISA results were comparable to ImmunoCAP, but the latter agreed more closely with clinical diagnosis.
Patients and controls
A total of 36 HCW were studied, of which 10 had no clinical symptoms of latex allergy; the remaining 26 subjects had clinically proven latex allergy [3, 5]. Among the 21 SB patients studied, 13 had clinical latex allergy . Latex allergy in health care workers was diagnosed by (a) a history of skin and respiratory symptoms often progressing from contact dermatitis through urticaria to asthma and anaphylaxis on latex contact, usually with latex glove powder inhalation, or (b) immediate wheal and flare skin reaction to latex glove antigens, (c) a history of reaction to cross-reactive latex antigens such as bananas or other fruits, and/or (d) serum IgE antibodies to latex glove extracts carried out by ELISA. Latex allergy in SB patients was diagnosed by a history of perioperative anaphylaxis and/or the demonstration of respiratory symptoms on latex glove powder contact, and/or the demonstration of antibody to latex antigens and a history of cross-reaction to food allergens . All sera were evaluated for latex specific IgE antibody using a Malaysian non-ammoniated latex extract, two glove extracts routinely used in our laboratory to confirm the diagnosis [11, 12].
Purified Latex Allergens and their Characteristics
Molecular Size kDa
Significance in the Diagnosis
Hev b 1
Biosynthesis of polyisoprene
Rubber elongation factor
Hev b 2
Beta 1-3-glucanase defense protein
Hev b 3
Biosynthesis of polyisoprene
Hev b 4
Micro helix protein
Hev b 5
Hev b 6
Hev b 7
Esterase inhibitor of polyisoprene
Hev b 8
Hev b 9
Hev b 10
Manganese superoxide dismutase
Hev b 13
Three of the allergens Hev b 2, Hev b 4, and Hev b 13 were purified from latex by the Malaysian laboratory (HYY) as previously described [5, 16, 17]. The genes for Hev b 1, 3, 5, 6, 7, 8, 9, and 10 were cloned from cDNA libraries and Hev b 1, 3, 5, and 6 were expressed in the Medical College of Wisconsin laboratory (VPK), while Hev b 7, 8, 9, and 10 were cloned and expressed in the University of Vienna laboratory (HB) [18, 27].
Characterization of latex antigens
The protein profile of the extract was studied by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Electrophoresis was carried out by loading 10 micrograms of proteins on a 12% SDS polyacrylamide mini gel and running at 200 mv/cm for 40 to 50 minutes . The gels were stained with Coomassie brilliant blue R-250 and the stained bands in the gel were compared and the molecular sizes ascertained. The reactivity of antigens to serum IgE was studied using pooled sera from HCW and SB patients with latex allergy and controls by ELISA and Western blot.
Latex specific IgE by ELISA
The MNA, Clone RRIM 600, glove extract antigens, and purified latex proteins were coated at a concentration of 5-μg protein/ml. All dilutions and coating concentrations of the antigens and reagents were derived from checkerboard titration using latex positive and negative sera. The ELISA was performed as previously described . Briefly, one hundred micro liters of the preparations were added to the wells of polystyrene micro titer plates (Immunolon II HB, Therma Lab Systems, Franklin, MA). The plates were incubated at room temperature for 3 hours, followed by a further incubation at 4°C overnight. After washing the plates with PBS, containing 0.05% Tween 20 (PBS-T), the wells were blocked with 0.5% BSA in PBS-T. The wells were again washed and 100-μl of 1:25 dilution of the serum added to each well, incubated at room temperature for 3 hours, and washed as before. One hundred-μl of biotinylated mouse, anti-human IgE monoclonal antibody (Zymed Laboratories, Inc., San Francisco, CA) was added to each well and the plates were incubated for 1 hour at room temperature, washed as before and 100 μl of 1:2000 dilution of streptavidin peroxidase was added to the wells. This was followed by incubation for 30 minutes and washing again. Finally, the peroxidase activity was developed with o-phenylenediamine substrate in citrate buffer. The color was developed for 15 minutes in a dark chamber and the reaction stopped by the addition of 25 μl of 2N H2SO4 solution. The color was read in an ELISA plate reader using a 490 nm filter (Molecular Devices; Sterling, VA). The optical density (O.D) values were corrected by subtracting the blank values and the average of three wells was taken. A value exceeding mean plus two standard deviation (SD) of HCW and SB patients without latex allergy was taken as a cut off value for positivity.
The Pharmacia ImmunoCAP was used to demonstrate latex specific IgE in the sera of patients and controls according to the instructions of the manufacturer. Both Hev b 5 amplified (rk82) and non-amplified (k82) ImmunoCAPs were used. The protocol of the manufacturer was followed, and a value of 0.35 kUA/L or more was considered positive.
The mean O.D values for all allergens were calculated and the results were analyzed by the multivariate analysis of variance (MANOVA). A P-value of 0.05 was considered significant. When a significant difference was detected, a stepwise discriminant analysis was also performed to select the significant allergens that delineate the positive and negative groups by their reactivity or non-reactivity with IgE by ELISA. The variables with P-value of < 0.05 were chosen as the significant variables, while the variables with P-value > 0.20 were removed at each step of the discriminant analysis. Using all the significant allergens, Fisher discriminant functions for the latex allergic and non-allergic HCW and SB subjects were calculated. Based on this, each case was assigned two Fisher discriminant scores, one for the latex allergic group and the other one for the non-allergic group. Each subject was classified into a group (latex allergic or non-allergic) based on the higher corresponding Fisher discriminant score value as the case may be [5, 28].
Characteristics of the antigens
Latex specific IgE in the sera
The binding of IgE to allergens Hev b 1 to Hev b 6 and Hev b 13 showed a significant difference (P < 0.05) between SB patients with and without latex allergy when studied individually. Hev b 7 to Hev b 10 failed to show any significant IgE binding reactivity between these two groups. Among the HCW patients with latex allergy studied, strong reactivity was detected only with Hev b 2, Hev b 5, Hev b 6, and Hev b 13. When all 11 purified latex proteins were used together and analyzed the data by MANOVA, a significant difference was detected with latex allergic and non-allergic subjects from both HCW and SB groups (P < 0.05).
Stepwise discriminant analysis of the ELISA data from SB patients selected Hev b 1, Hev b 3, and Hev b 6 and together these antigens delineated all the latex allergic and non-allergic subjects. The Fisher discrimination function for the positive group is -10.549 + 11.569 Hev b 1 -9.189 Hev b 3 + 5.443 Hev b 6, and for the negative group is -0.694 + 0.098 Hev b 1 -0.068 Hev b 3 + 0.027 Hev b 6. All the SB subjects studied could be classified into latex allergic or non-allergic, and the specificity and sensitivity were found to be 100% by ELISA using these allergens.
Sensitivity and specificity of purified latex allergens in the diagnosis of latex allergy in health care workers (HCW)
Overall Correct Agreement
Hev b 6
Hev b 2, 5, 6, & 13
All allergens Hev b 1 to Hev b 13
The results indicate that crude NRL allergens including an extract from Clone RRIM600 demonstrate strong reactivity with IgE from latex allergic HCW patients. Both glove extracts, in spite of their differences in protein content and failure to show distinct bands in SDS-PAGE, demonstrated similar reactivity as shown by MNA and Clone RRIM600 with both groups of patients. The single patient negative by unamplified ImmunoCAP reacted strongly to the amplified ImmunoCAP with Hev b 5 indicating that Hev b 5 is important for the diagnosis of some of the HCW patients with latex allergy. None of the other purified latex allergens studied reacted with IgE from this patient. Our results indicate that Hev b 1, 3, 4, and 7 through 10 have little or no value in the demonstration of IgE in HCW patients with latex allergy. In a previous study, we have shown that Hev b 2, 6, and 7 were useful in demonstrating IgE in the sera of HCW patients with latex allergy . Since we did not test Hev b 5 and 13 in the previous study, the present results indicate a more complete representation of all the relevant latex allergens and their reactivity with the sera from different groups of patients and controls. The results of the present study suggest the usefulness of Hev b 2, 5, 6, and 13 together in the diagnosis of latex allergy in HCW.
SB patients with latex allergy showed antibody responses to a different set of latex allergens. Both ELISA and ImmunoCAP showed strong agreement in demonstrating latex specific IgE in the sera of most of these patients. The findings indicate that a combination of Hev b 6 and Hev b 1 or 3 would demonstrate specific IgE in the sera of all patients with SB and latex allergy.
Although crude latex antigens are efficient in demonstrating IgE antibodies in latex allergic patients, such extracts are not appropriate as standardizable allergen reagents due to the inherent variability, complexity of allergenic components, and in the presence of cross reactive allergens. The present study suggests that by selecting significant antigens and by reconstituting known amounts of purified allergens, it may be possible to obtain standardizable preparations to demonstrate IgE antibody in the sera of HCW and SB patients with latex allergy. From the present study and from previous multi-center studies, it has been shown that the presence of latex specific IgE in HCW patients' sera can be demonstrated using a mixture of Hev b 2, 5, 6, and 13 and in SB patients with latex allergy by the use of Hev b 6 along with Hev b 1 or Hev b 3. It is not possible to derive a cut-off value for delineating the allergic patients from normal controls due to the high variability in the responses of the patients. However, additional patients may be studied before finally selecting the allergens and their proportions in the mixture for a more standardizable reagent and for devising a delineation titer.
The present study suggests the need to develop more specific reliable and reproducible allergen preparations for in vitro detection of latex allergen specific IgE. Kim and coworkers demonstrated that specific IgE levels to latex allergens in the sera of patients were symptom dependent and that patients with asthma showed higher levels of specific IgE compared to those with dermatitis alone [29, 30]. Although other investigators demonstrated false positives and false negative reactions with ImmunoCAP, Alastat and HY-TEC methods, in the present study our results were more clear -cut with less false positive and false negative reactions [7, 8]. In the present study, we have observed a more stronger reactivity with patient serum by Hev b 5 complemented ImmunoCAP compared to regular ImmunoCAP. However, the Hev b 5 amplified CAPs also showed more reactivity with normal control subjects without latex allergy. Moreover, the reactivities of HCW and SB patients' serum IgE with the purified antigens were more consistent than with crude latex extracts and no false reactivity was detected. Taken together, the present results indicate that ImmunoCAP system using purified relevant allergens, could be more dependable and reliable in in vitro demonstration of latex allergen specific IgE in the sera of latex allergic patients. The results suggest that a combination of Hev b 2, 3, 5, 6, and 13 would demonstrate IgE antibody in the majority of latex allergic patients.
The results indicate that ImmunoCAP, particularly amplified with Hev b 5, was useful in demonstrating specific IgE in the sera of latex allergic patients. When all purified latex allergens were used together in ELISA, about 89% of patients with latex allergy were correctly identified. We conclude from these results that selection of significant recombinant allergens and reconstitution of these purified antigens in immunoassays, such as ELISA, will provide standardizable reagents for demonstrating specific IgE in the sera of patients with latex allergy. These selected purified allergens can be used for more reliable results in automated assays such as ImmunoCAP.
Supported by the US Veterans Affairs, CDC-NIOSH #U60/CCU514541-01, Ansell International, Children's Research Institute of the Children's Hospital of Wisconsin, the Austrian Science Fund Grant #P12838-GEN, and by the Ministry of Science, Technology, and Environment, Malaysia under IRPA Grant 06-04-04-0001.
Part of this data was presented at the World Allergy Organization Congress-XVIII ICACA, Vancouver, Canada, September 2003
The technical assistance of Laura Castillo and Abe Resnick and the editorial assistance of Donna Schrubbe are gratefully acknowledged.
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