Science behind the discovery of IgE
2005; Elsevier BV; Volume: 115; Issue: 3 Linguagem: Inglês
10.1016/j.jaci.2004.12.007
ISSN1097-6825
Autores Tópico(s)Asthma and respiratory diseases
ResumoThe race for identification of the reagin or serum factor that could spontaneously sensitize skin and mediate a positive immediate-type skin reaction began in 1921 with the report of Prausnitz and Kustner.1Prausnitz C, Kustner H. Studien uber Uberempfindlicht. Centralb Bakerterial 1 Abt Orgi 1921;86:160-9. Published in English, in: Gel PGH, Coombs RRA, editors. Clinical aspects of immunology. Oxford Blackwell; 1962. p. 808-16.Google Scholar In their classic experiment, Prausnitz passively sensitized the skin in his forearm to fish by injecting serum from his coworker allergic to fish, Kustner. The following day, Prausnitz had an immediate-type wheal and flare, or so-called P-K reaction, after injection of fish extract into the same site in the skin. A detailed account of this exciting discovery has been eloquently presented in the Allergy Archives of the Journal,2Cohen S.G. Prausnitz and Kustner phenomenon: the P-K reaction.J Allergy Clin Immunol. 2004; 114: 705-710Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar and it is not further discussed here. Once human serum was known to carry the reagin, many investigators attempted to identify it over a period of more than 40 years. Eventually, 2 groups took advantage of newly developed analytical methods for serum protein fractionation and the availability of IgE myeloma proteins and adsorbed IgE (reagin-γE-ND) specific antisera. They would independently arrive at the conclusion in 1967 that the reagin was in fact a unique immunoglobulin class.3Bennich H.H. Ishizaka K. Johansson S.G. Rowe D.S. Stanworth D.R. Terry W.D. Immunoglobulin E: a new class of human immunoglobulin.Immunochemistry. 1968; 5: 327-328Crossref PubMed Scopus (22) Google Scholar This report reviews the scientific observations that led them to the discovery that IgE is a unique human immunoglobulin class and the elusive reagin or skin-sensitizing factor in serum. Once the science has been discussed, the report provides a personal reflection on the significance that the discovery of IgE has played in improving the clinical diagnosis and management of patients with allergy and facilitating basic research involved in studying mechanisms of human allergic disease. By 1960, several analytical techniques including ammonium sulfate precipitation, Cohn fractionation with ethanol, zone electrophoresis, anion exchange resin chromatography, and sucrose density gradient ultracentrifugation had been used by researchers to conclude that reaginic antibodies were different from IgG (γG) and IgM (γM). Many of the key scientific observations leading to this conclusion are listed in Table I. After identification of IgA (γA, originally known initially as β2a globulin) in 1959, many researchers began examining the potential association between human IgA and reaginic activity in serum. The γA fraction of human atopic sera was initially shown to have skin-sensitizing activity, and γA globulin but not γG or γM from normal serum was able to block passive sensitization of human skin with reagin. These and other experimental data (Table I) lead some scientists to conclude that reaginic activity was associated with IgA. Others, however, remained skeptical about this conclusion because there was a possibility of impurities in the IgA preparations containing the reaginic activity that might not have been detected by the immunochemical methods available at the time. The sensitivity of the P-K reaction in human beings was thought to be comparable with that of the passive cutaneous anaphylaxis (PCA) reaction in guinea pigs, in which 0.03 to 0.1 μg nitrogen/mL antibody was required for a positive reaction. However, because some reaginic sera with a γA concentration of 0.3 mg nitrogen/mL titered out to 1:10,000, this would have meant that all of the γA in these sera would have had be specific for a single allergen specificity (which was considered unlikely). To shed further doubt on the association between reaginic activity and γA, a serum was identified with reaginic activity that lacked any detectable γA. Finally, human anti-γA isoagglutinin studies indicated no detectable γG, γA, or γM antibodies in sensitized skin.19Loveless M.H. Reagin production in a healthy male who forms no detectable β2a immunoglobulins.Fed Proc. 1964; 23: 403-409Google Scholar, 20Ishizaka K. Ishizaka T. Sugahara T. Biological activity of soluble antigen-antibody complexes, VII: role of an antibody fragment in the induction of biological activities.J Immunol. 1962; 88: 690-694Google ScholarTable ISelected historical events associated with the discovery of IgE as the reaginDateObservationMethodReferences1930-1937Reaginic antibodies present in pseudoglobulin fraction rather than euglobulin fraction of human serumAmmonium sulfate precipitation4Scherrer E.L. The distribution of reagins in the blood plasma.J Allergy. 1930; 2: 467-472Abstract Full Text PDF Scopus (4) Google Scholar, 5Stull A. Sherman W.B. Cooke R.A. The association with pseudoglobulin of the skin sensitizing substance of allergic hay fever serum.J Allergy. 1937; 9: 7-14Abstract Full Text PDF Scopus (1) Google Scholar1952Reaginic activity concentration in fraction III containing principally β-globulinCohn ethanol-low temperature Fractionation6Vaughan J.H. Favour C.B. Jaffee I.H. Partition of the skin sensitizing antibody among alcohol-fractionated plasma proteins.J Allergy. 1952; 23: 489-492Abstract Full Text PDF PubMed Scopus (2) Google Scholar1954-1957Maximum reaginic activity found in β to γ 1-globulin regionZone electrophoresis7Campbell D.H. Cann J.R. Friedman T.B. Brown R. The relation of allergy reagins to electrophoretic components of serum.Science. 1954; 119: 289-291Crossref PubMed Scopus (1) Google Scholar, 8Sehon A.H. Fyles T.W. Rose B. Electrophoretic separation of skin sensitizing antibody from the sera of ragweed sensitive patients.J Allergy. 1955; 26: 329-339Abstract Full Text PDF PubMed Scopus (3) Google Scholar, 9Cann J.R. Loveless M.H. Biophysical characterization of reaginic and blocking sera.J Allergy. 1957; 28: 379-391Abstract Full Text PDF PubMed Scopus (2) Google Scholar1957-1959DEAE γG immunoglobulin fraction usually lacked reaginic activityDiethyl amino ethyl cellulose (DEAE) column chromatography10Humphrey J.H. Porter R.R. Reagin content of chromatographic fractions of human gamma globulin.Lancet. 1957; 272: 196-197Abstract PubMed Scopus (5) Google Scholar, 11Stanworth D.R. Studies on the physio-chemical properties of reagin to horse dandruff.Immunology. 1959; 2: 384-402PubMed Google Scholar1961-1964Reaginic activity found at 7.8 (average) between 7S (monomeric) and 19S (pentameric) fractionsSedimentation coefficient by sucrose density gradient ultracentrifugation12Gyenes L. Gordon J. Sehon A.H. Ultracentrifugal characterization of antibodies in sera of ragweed sensitive individuals.Immunology. 1961; 4: 177-191PubMed Google Scholar, 13Andersen B.R. Vannier W.E. The sedimentation properties of the skin sensitizing antibodies of ragweed sensitive patients.J Exp Med. 1964; 120: 31-42Crossref PubMed Scopus (5) Google Scholar1962-1964Reports that γA fraction of human atopic sera had skin-sensitizing activityImmunoprecipitation14Heremans J.F. Vaerman J.P. β2a Globulin as a possible carrier of allergic reaginic activity.Nature. 1962; 193: 1091-1092Crossref PubMed Scopus (14) Google Scholar, 15Vaerman J.P. Epstein W. Fudenberg H. Ishizaka K. Direct demonstration of reagin activity in purified γ1a globulin.Nature. 1964; 203: 1046-1048Crossref PubMed Scopus (10) Google Scholar, 16Fireman P. Vannier W.E. Goodman H.C. The association of skin sensitizing antibody with the β2a globulins in sera from ragweed sensitive patients.J Exp Med. 1963; 117: 603-620Crossref PubMed Scopus (22) Google Scholar1963γA globulin but not γG or γM from normal serum blocked passive sensitization of human skin with reaginP-K testing17Ishizaka K. Ishizaka T. Hornbrook M.M. Blocking of Prausnitz-Kustner sensitivity with reagin by normal human β2a globulin.J Allergy. 1963; 34: 395-403Abstract Full Text PDF PubMed Scopus (16) Google Scholar1963Ragweed-specific IgA (γA) antibodies detected in sera of patient with allergyRadioimmunoelectrophoresis18Yagi Y. Maier P. Pressman D. Arbesman C.E. Reisman R.E. The presence of the ragweed binding antibodies in the β2a, β2m and γ globulins of sensitive individuals.J Immunol. 1963; 91: 83-89PubMed Google Scholar1964Reaginic activity detected in human serum that lacked detectable γAImmunoprecipitation19Loveless M.H. Reagin production in a healthy male who forms no detectable β2a immunoglobulins.Fed Proc. 1964; 23: 403-409Google Scholar1962Human anti-A isoagglutinin studies indicated no γG, γA, or γM antibodies in sensitized skinImmunohistology20Ishizaka K. Ishizaka T. Sugahara T. Biological activity of soluble antigen-antibody complexes, VII: role of an antibody fragment in the induction of biological activities.J Immunol. 1962; 88: 690-694Google Scholar1966Reaginic activity did not parallel IgG or IgA concentrations in fractions of serum from patients allergic to ragweed and egg processed with DEAE chromatography and Sephadex G-200 (Pharmacia, Uppsala, Sweden) gel filtrationP-K test, immunodiffusion21Ishizaka K. Ishaizaka T. Physicochemical properties of reaginic antibody, I: association of reaginic activity with an immunoglobulin other than γA and γG globulin.J Allergy. 1966; 37: 169-185Abstract Full Text PDF PubMed Scopus (113) Google Scholar1966Precipitation of γA and γD from reagin-rich serum fractions with added γA isoagglutinin resulted in reaginic activity remaining in supernatant and indication that the reaginic antibody is not associated with γG, γA, γM, or γD globulins; labeled γE-globulinChromatography, precipitation, electrophoresis, immunodiffusion, hemagglutination, P-K test22Ishizaka K. Ishizaka T. Lee E.H. Physicochemical properties of reaginic antibody, II: characteristic properties of reaginic antibody different from γA isohemagglutinin and γD globulin.J Allergy. 1966; 37: 336-349Abstract Full Text PDF PubMed Scopus (29) Google Scholar, 23Ishizaka K. Ishizaka T. Physicochemical properties of reaginic antibody, III: further studies on the reaginic antibody in γA globulin preparation.J Allergy. 1966; 38: 108-119Abstract Full Text PDF PubMed Scopus (24) Google Scholar, 24Ishizaka K. Ishizaka T. Hornbrook M.M. Physicochemical properties of reaginic antibody, IV: presence of a unique immunoglobulin as a carrier of reaginic activity.J Immunol. 1966; 97: 75-85PubMed Google Scholar1996Confirmation of lack of correlation between reaginic activity and γG, γA, or γD concentrations in reaginic seraChromatography–P-K27Perelmutter L. Rose B. Goodfriend L. The relationship between the skin sensitizing antibody and gA protein in the sera of ragweed allergic individuals.J Allergy. 1966; 37: 236-245Abstract Full Text PDF PubMed Scopus (3) Google Scholar1966-1967Lack of association of reaginic activity with γG2, γG3, and γG4, supporting conclusion that reaginic antibody belongs to a unique immunoglobulin class not yet describedChromatography, precipitation, electrophoresis, immunodiffusion24Ishizaka K. Ishizaka T. Hornbrook M.M. Physicochemical properties of reaginic antibody, IV: presence of a unique immunoglobulin as a carrier of reaginic activity.J Immunol. 1966; 97: 75-85PubMed Google Scholar, 28Ishizaka K. Ishizaka T. Terry W.D. Antigenic structure of γE globulin and reaginic antibody.J Immunol. 1967; 99: 849-858PubMed Google Scholar1967Preparation of γE antiserum and use of radioimmunodiffusion to show that γE precipitin bands with serum from individuals allergic to ragweed bind radioiodinated antigen E (Amb a 1)Radioimmunodiffusion28Ishizaka K. Ishizaka T. Terry W.D. Antigenic structure of γE globulin and reaginic antibody.J Immunol. 1967; 99: 849-858PubMed Google Scholar, 29Ishizaka K. Ishizaka T. Hornbrook M.M. Allergen binding activity of γE, γG and γA antibodies in sera from atopic patients: in vitro measurements of reaginic antibody.J Immunol. 1967; 98: 480-501Google Scholar, 30Ishizaka K. Ishizaka T. Identification of γE antibodies as a carrier of reaginic activity.J Immunol. 1967; 99: 1187-1198PubMed Google Scholar1967Identification and physicochemical characterization of γE-myeloma (ND)Chromatography, precipitation, electrophoresis, immunodiffusion radioimmunoassay32Johansson S.G.O. Bennich H. Immunological studies of an atypical myeloma immunoglobulin.Immunology. 1967; 13: 381-394PubMed Google Scholar, 34Johansson S.G.O. Raised levels of a new immunoglobulin class (IgND) in asthma.Lancet. 1967; 2: 951-953Abstract PubMed Google Scholar Open table in a new tab By the mid-1960s, Drs Kimishige and Teruko Ishizaka had begun repeating some of their earlier experiments, this time by using more specific antisera for reagin and chromatographically separated fractions of human serum from individuals allergic to ragweed and egg. They observed that skin-sensitizing activity in the chromatographic fractions of these sera did not parallel γA or γG levels. Precipitation of γG and γA from these fractions with γG and γA specific antisera left reaginic activity in the supernatant, which was then precipitated out with anti-κ and anti-λ light chain antisera. Together, these results indicated that skin-sensitizing reagin was an antibody that was neither IgG nor IgA but possibly a unique protein having light chains of immunoglobulins.21Ishizaka K. Ishaizaka T. Physicochemical properties of reaginic antibody, I: association of reaginic activity with an immunoglobulin other than γA and γG globulin.J Allergy. 1966; 37: 169-185Abstract Full Text PDF PubMed Scopus (113) Google Scholar These results were confirmed with a reaginic serum fraction in which γA isoagglutinin was added to insure IgA precipitation. The Ishizakas then went on to show the sucrose sedimentation velocity of reaginic antibody was between the polymeric (10.5S) and monomeric (7S) forms of γA. γA isoagglutinin also exhibited a faster electrophoretic mobility than reaginic antibodies.22Ishizaka K. Ishizaka T. Lee E.H. Physicochemical properties of reaginic antibody, II: characteristic properties of reaginic antibody different from γA isohemagglutinin and γD globulin.J Allergy. 1966; 37: 336-349Abstract Full Text PDF PubMed Scopus (29) Google Scholar, 23Ishizaka K. Ishizaka T. Physicochemical properties of reaginic antibody, III: further studies on the reaginic antibody in γA globulin preparation.J Allergy. 1966; 38: 108-119Abstract Full Text PDF PubMed Scopus (24) Google Scholar Multiple groups were able to confirm that γA precipitin bands from ragweed-sensitive sera bound radioactive ragweed allergen and that anti-ragweed γA antibody was precipitated by anti-γA antibody, but it left essentially all of the reaginic activity in the supernatant.24Ishizaka K. Ishizaka T. Hornbrook M.M. Physicochemical properties of reaginic antibody, IV: presence of a unique immunoglobulin as a carrier of reaginic activity.J Immunol. 1966; 97: 75-85PubMed Google Scholar, 25Reisman R.E. Arbesman C.E. Yagi Y. Radioimmunoelectrophoresis of ragweed binding antibodies in allergic sera.J Allergy. 1965; 36: 362-365Abstract Full Text PDF Scopus (3) Google Scholar, 26Ishizaka K. Ishizaka T. Hornbrook M.M. Physicochemical properties of reaginic antibody, V: correlation of reaginic activity with gamma-E-globulin antibody.J Immunol. 1966; 97: 840-853PubMed Google Scholar Only few groups such as Fireman et al16Fireman P. Vannier W.E. Goodman H.C. The association of skin sensitizing antibody with the β2a globulins in sera from ragweed sensitive patients.J Exp Med. 1963; 117: 603-620Crossref PubMed Scopus (22) Google Scholar continued to believe that reaginic activity was associated with γA because their γA antisera precipitated the reaginic activity. In retrospect, the antiserum used by this group for precipitation must have contained antibodies specific for IgE as a result of a low level of IgE contaminant in the γA preparation used for rabbit immunization. To prove that reaginic antibodies belonged to a distinct immunoglobulin class, the Ishizaka group prepared rabbit antibodies to the reaginic-rich fractions of serum from ragweed-sensitized individuals. The antisera were then adsorbed against normal human γG and myeloma γA and γD proteins to render them specific for reagin. The reagin-rich supernatants from γA and γG precipitation studies produced a distinct precipitin line with this reagin-specific rabbit antiserum. The precipitin bands were also shown to bind radioiodinated purified ragweed antigen E (Amb a 1). The reagin precipitin line did not contain γG, γA, γM, or γD, and the Ishizakas tentatively designated the antibody γE-globulin.24Ishizaka K. Ishizaka T. Hornbrook M.M. Physicochemical properties of reaginic antibody, IV: presence of a unique immunoglobulin as a carrier of reaginic activity.J Immunol. 1966; 97: 75-85PubMed Google Scholar, 29Ishizaka K. Ishizaka T. Hornbrook M.M. Allergen binding activity of γE, γG and γA antibodies in sera from atopic patients: in vitro measurements of reaginic antibody.J Immunol. 1967; 98: 480-501Google Scholar Confirmation of γE's association with reaginic activity continued with repeat studies using fractionated reaginic sera from multiple ragweed-sensitive patients. γE-globulin specific antiserum was used in radioimmunodiffusion studies to show that precipitated antibody bands also bound radioiodinated purified antigen E.29Ishizaka K. Ishizaka T. Hornbrook M.M. Allergen binding activity of γE, γG and γA antibodies in sera from atopic patients: in vitro measurements of reaginic antibody.J Immunol. 1967; 98: 480-501Google Scholar, 30Ishizaka K. Ishizaka T. Identification of γE antibodies as a carrier of reaginic activity.J Immunol. 1967; 99: 1187-1198PubMed Google Scholar γE-globulin was also shown to contain κ and λ light chains, and it was shown to not be associated with any of the subclasses of IgG or IgA.31Ishizaka K. Ishizaka T. Human reaginic antibodies and immunoglobulin E.J Allergy. 1968; 42: 330-363Abstract Full Text PDF PubMed Scopus (127) Google Scholar In 1967, Drs S.G.O. Johansson and Hans Bennich described an E myeloma protein (myeloma ND [after the patient's initials]) with physical and chemical properties that were similar to those of the γE-globulin used in the Ishizakas' experiments.32Johansson S.G.O. Bennich H. Immunological studies of an atypical myeloma immunoglobulin.Immunology. 1967; 13: 381-394PubMed Google Scholar, 33Johansson S.G.O. Bennich H. Wide L. A new class of immunoglobulin in human serum.Immunology. 1968; 14: 265-272PubMed Google Scholar The anti-IgND serum specific for the Fc portion of the ND myeloma produced a single precipitin band (line of identify) in immunodiffusion studies. Anti-IgND also precipitated reagin activity from a ragweed-sensitive serum. The molecular weight of the IgND myeloma protein was slightly higher than that of γG, and the monomeric form of γA and its carbohydrate content was similar to γM.32Johansson S.G.O. Bennich H. Immunological studies of an atypical myeloma immunoglobulin.Immunology. 1967; 13: 381-394PubMed Google Scholar By using a newly developed radioimmunosorbent test (RIST) that used IgND specific antiserum as a capture and labeled detection antibody, the Swedish group measured and reported the concentration of total IgND in sera of nonallergic (normal) individuals to range from 0.1 to 0.7 μg/mL, with an average concentration of 0.33 μg/mL.34Johansson S.G.O. Raised levels of a new immunoglobulin class (IgND) in asthma.Lancet. 1967; 2: 951-953Abstract PubMed Google Scholar This contrasted with IgG levels ranging from 7 to 15 mg/mL in the human serum. With the RIST assay, sera from atopic individuals with asthma and hay fever were shown to contain elevated levels of IgND.35Bennich H, Johansson SGO. Studies on a new class of human immunoglobulin, II: chemical and physical properties. In: Lundquist A, Wiksell H, editors. Nobel Symposium III. Stockholm: 1967: 99-103.Google Scholar Wide et al36Wide L. Bennich H. Johannson S.G.O. Diagnosis by an in vitro test for allergen antibodies.Lancet. 1967; 2: 1105-1107Abstract PubMed Google Scholar then modified the RIST, replacing the solid phase anti-IgND with a solid phase allergen (allergosorbent) and using the same radiolabeled antihuman IgND as a detection antibody. The RAST was thus born as the first clinically useful assay for allergen-specific IgE antibody in human serum.36Wide L. Bennich H. Johannson S.G.O. Diagnosis by an in vitro test for allergen antibodies.Lancet. 1967; 2: 1105-1107Abstract PubMed Google Scholar A new era in the diagnosis and research of allergic disease dawned with a World Health Organization (WHO) meeting in which the research findings of the 2 groups were merged. After a consensus that was arrived at at the WHO International Reference Center for Immunoglobulins in Lausanne, Switzerland, in February 1968, the term IgE was accepted as that component in serum that carried reaginic activity.37Bennich H.H. Ishizaka K. Johansson S.G. Rowe D.S. Stanworth D.R. Terry W.D. Immunoglobulin E: a new class of human immunoglobulin.Immunology. 1968; 3: 323-324Google Scholar IgE replaced other terminology such as γE-globulin, IgND, and reagin that had been previously used in the literature to refer to skin-sensitizing antibodies present in serum of individuals with allergy. IgE was shown to have antigenic determinants in common with the other 4 human immunoglobulin classes (IgG, IgA, IgM, and IgD), and IgE from nonmyeloma sources was shown to contain both light chains (κ and λ). Studies with 2 IgE myeloma proteins (ND and PS) confirmed the molecular weights of the IgE heavy and light polypeptide chains as 75,500 and 22,500, respectively.38Dorrington K. Bennich H.H. Structure-function relationships in human immunoglobulin E.Immunol Rev. 1978; 41: 3-25Crossref PubMed Scopus (123) Google Scholar IgE's overall molecular weight was 180,000, and its sediment coefficient was shown to be 7.925 (Table II).32Johansson S.G.O. Bennich H. Immunological studies of an atypical myeloma immunoglobulin.Immunology. 1967; 13: 381-394PubMed Google Scholar The heat-labile nature of IgE was shown to be localized to the Fc region, and it correlated with structural changes within the Cε3 and Cε4 regions but not the Cε2 region of the molecule.Table IIPhysicochemical properties of human immunoglobulinsPropertyγGγMγAγDγEMyeloma NDReaginSedimentation coefficient S20 w6.6186.67.08.08.2∼8.0Electrophoretic mobilityγ1-γ2γ1γ1γ1γ1γ1γ1Molecular weight150,000900,000180,000NANA200,000NACarbohydrate %2.911.87.5NANA10.7NAModified from J Allergy Clin Immunol, Volume 42, Ishizaka K, Ishizaka T, “Human reaginic antibodies and immunoglobulin E,” Pages 330-63, Copyright 1968, with permission from the American Academy of Allergy, Asthma and Immunology. Open table in a new tab Modified from J Allergy Clin Immunol, Volume 42, Ishizaka K, Ishizaka T, “Human reaginic antibodies and immunoglobulin E,” Pages 330-63, Copyright 1968, with permission from the American Academy of Allergy, Asthma and Immunology. The identification of IgE as the reagin has had a major effect on all aspects of the clinical diagnosis and treatment of patients with allergy, as well as on research investigations into the immunochemical pathways involved in the induction of effector cell degranulation and the elicitation of allergic symptoms. After acceptance of IgE as the reagin in 1968, the Swedish investigators moved rapidly to develop a clinically useful serological assay for total (RIST) and allergen-specific IgE antibody (RAST). For the first time, the diagnosis of human allergic disease could be accomplished by an in vitro alternative to skin testing that involved detection of allergen-specific IgE in serum. The first commercially available RAST for clinical laboratories used a paper disk allergosorbent to bind specific IgE antibody and radioiodinated antihuman IgE Fc was then used to detect bound IgE.39DeFilippi I. Yman L. Schroder H. Clinical accuracy of updated version of the Phadebas RAST test.Ann Allergy. 1981; 46: 249-255PubMed Google Scholar Bound radioactivity detected in the assay was translated into estimates of IgE and IgE antibody concentration by interpolation from a reference curve constructed with 5 dilutions of IgE antibirch reference serum. Total IgE results were reported in kilo international units per liter and specific IgE antibody levels in Phadebas relative units per milliliter. These results were often translated into arbitrarily chosen class groupings that were analogous to those being used to grade skin tests. This serological assay for identifying the presence of IgE antibody (sensitization to an allergen) was a useful diagnostic tool, especially for the evaluation of individuals with severe eczema or dermagraphism and children who were being investigated for allergies. Over the 36 years since the 1968 WHO consensus meeting, many versions of IgE antibody assays have come and gone. It was clear from a consensus meeting held by the National Committee on Clinical Laboratory Standards40Matsson P, Hamilton RG, Adkinson NF Jr, Esch R, Homburger H, Maxim P, et al. Evaluation methods and analytical performance characteristics of immunological assays for human IgE antibody of defined allergen specificities. Consensus Guideline I/LA20-A. Wayne (PA): National Committee on Clinical Laboratory Standards; 1997.Google Scholar that sufficient quantities of human serum containing IgE antibodies to each of the ∼200 clinically important allergen specificities would not be available to calibrate each allergen-specific IgE antibody test with homologous standards. Thus, an alternative approach was adopted, the method of heterologous interpolation,41Butler J.E. Hamilton R.G. Quantitation of specific antibodies: methods of expression, standards, solid phase considerations and specific applications.in: Butler J.E. Immunochemistry of solid phase immunoassays. CRC Press, Boca Raton (FL)1991: 173-198Google Scholar in which allergen-specific IgE results were interpolated from a (heterologous) total serum IgE dose response curve. If the assay response (CPM-bound, OD, or fluorescent units) obtained for the total IgE calibration curve paralleled the responses obtained in the same assay with dilutions of test sera in the allergen-specific IgE antibody component of the assay, then the assay could be considered quantitative. Fortunately, this calibration scheme maintained parallelism, and the total IgE calibration curve has been traced in all clinically used IgE antibody assays to well-characterized human serum reference preparations with defined levels of total serum IgE.42Rowe D.S. Tackett L. Bennich H. Ishizaka K. Johansson S.G.O. Anderson S.G. A research standard for human serum immunoglobulin E.Bull World Health Organ. 1970; 43: 609-611PubMed Google Scholar, 43Rowe D.S. Grab B. Anderson S.G. An international reference preparation for human serum immunoglobulin E.Bull World Health Organ. 1973; 49: 310-321Google Scholar, 44Seagroatt V. Anderson S.G. The second international reference preparation for human serum immunoglobulin E and the first British standard for human serum immunoglobulin E.J Biol Stand. 1981; 9: 431-437Crossref PubMed Scopus (34) Google Scholar, 45Evans R. A U.S. reference for human immunoglobulin E.J Allergy Clin Immunol. 1981; 68: 79-82Abstract Full Text PDF PubMed Scopus (9) Google Scholar The quantitative nature especially of the commercially available third-generation allergen-specific IgE assays has allowed the identification of IgE antibody 95% confidence limits for some food allergen specificities. The consequence has been the option to avoid cumbersome and risky double-blind, placebo-controlled food challenges when assessing some children for the presence of clinical sensitivity to some allergic foods.46Hamilton R.G. Adkinson Jr., N.F. Clinical laboratory assessment of IgE-dependent hypersensitivity.J Allergy Clinical Immunol. 2003; 111: 687-701Abstract Full Text Full Text PDF Scopus (126) Google Scholar, 47Hamilton R.G. Adkinson Jr., N.F. In vitro assays for IgE mediated sensitivities.J Allergy Clin Immunol. 2004; 114: 213-225Abstract Full Text Full Text PDF PubMed Scopus (157) Google Scholar With regard to management of allergic disease, the identification of IgE as the reagin has led to development and licensing of anti-IgE (Omalizumab, Xolair [Genentech and Novartis, S. San Francisco, Calif]) therapy. Pretreatment total serum IgE levels are used to define the dose of Omalizumab to be administered. For traditional immunotherapy, pretreatment serological analyses for IgE antibody can aid in identifying the allergic sensitivities of patients with allergy so immunotherapy can be more effectively targeted. Changes in IgE antibody levels can also be used to assess the efficacy of treatment in patients with allergy receiving a combination of avoidance, pharmacotherapy, immunotherapy, and anti-IgE therapy. Finally, as more recombinant allergens are identified and purified, more precise characterization of the patient's IgE antibody specificity may allow more targeted therapy.48Hiller R. Laffer S. Harwanegg C. Huber M. Schmidt W.M. Twardosz A. et al.Microarrayed allergen molecules: diagnostic gatekeepers for allergy treatment.FASEB J. 2002; 16: 414-416PubMed Google Scholar The competitive inhibition format of the RAST, and its modern nonisotopic counterparts such as the ImmunoCAP System (Pharmacia, Kalamazoo, Mich) and Immulite 2000 (Diagnostic Products Corporation, Los Angeles, Calif), have become important assays to allergen manufacturers and regulatory agencies for assessing allergenic potency of biological extracts and to the food industry for detecting and quantifying residual allergenic proteins in food products for purposes of labeling. More specifically, the power of IgE-based competitive inhibition immunoassays to quantify the presence and amount of allergens with immunoreactive epitopes from egg (lysozyme) and soy and wheat has remained unsurpassed in comparison with total protein assays, antigen immunoassays, and PCR-based DNA assays. Possibly nowhere has the discovery of IgE had such a large effect as on the investigator performing research on human allergic diseases. Selection of subjects with allergy for studies has been enhanced with quantitative total and allergen-specific IgE antibody assays. Often inclusion and exclusion criteria are set on the basis of the presence of certain IgE antibody specificities or levels of total serum IgE. IgE antibodies have been extensively used to study the presence of IgE and Fcɛ receptors on mast cell and basophil surfaces. Basophil mediator release assays have become a useful research and clinical tool for qualifying individuals who have discordant skin and serologic tests for IgE antibody. In vitro IgE-mediated activation of basophils has become a useful indicator of activation to identify better the biochemical pathways leading to in vivo mediator release. Even studies to identify genes that associate with allergy and asthma have used total and allergen-specific IgE antibody levels in serum to define probands and investigate associations between gene polymorphisms and allergic disease. The discovery of IgE has had sweeping effects on all aspects of research in the field of human allergic disease. We owe a debt of gratitude to all those researchers, especially Drs Ishizaka, Johannson, and Bennich, who worked tirelessly with early immunochemical methods and often less than specific antisera to identify IgE as the reagin or skin-sensitizing antibody. Knowledge that IgE is the reagin that mediates allergic reactions has touched every aspect of our discipline. It has put a face on the elusive reagin that has plagued patients with allergy since the beginning of recorded time. Knowledge of its role in the immediate-type hypersensitivity reaction has led to improved diagnostic methods and enhanced clinical management. The discovery of IgE is that critical event in history that will have a lasting effect on the study of human allergic disease into our distant future.
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