Immunoelectrophoresis: a Possible Source of Error
Total Page:16
File Type:pdf, Size:1020Kb
J Clin Pathol: first published as 10.1136/jcp.33.5.500 on 1 May 1980. Downloaded from J Clin Pathol 1980; 33: 500-504 Detection of monoclonal immunoglobulins by immunoelectrophoresis: a possible source of error AM SMITH, RA THOMPSON, AND MR HAENEY From the Supra Regional Protein Reference Unit, Department ofImmunology, East Birmingham Hospital, Bordesley Green East, Birmingham, B9 5ST, UK SUMMARY The technique of immunoelectrophoresis (IEP) is widely employed in the qualitative analysis of serum immunoglobulins. The most commonly used support media are agarose or agar gels, but the mobility of immunoglobulins is different in these two media. The presence of a small amount of a cathodal monoclonal immunoglobulin G may not be detected on IEP in agar if it is masked by larger amounts of polyclonal immunoglobulin of the same class. In these circum- stances the use of agarose imparts to the monoclonal protein a different mobility from that of the bulk of the serum IgG and allows its positive identification. Since its introduction' immunoelectrophoresis (IEP) phoresis may then be interpreted as an artefact. has proved a valuable tool in the qualitative investi- This paper reports five cases in which the presence gation of proteins, particularly human serum of a monoclonal protein could not be shown immunoglobulins. Classically, the technique involves convincingly on IEP in agar, although all were the separation of proteins by electrophoresis in a clearly visible after IEP in agarose. gel support medium, followed by visualisation of the separated proteins using specific antisera. Initial Material and methods separation of the proteins depends on the charge carried by each protein. Polyclonal immuno- IEP in agar was carried out using 1-5 % agar in http://jcp.bmj.com/ globulins, being of varying amino-acid composition, 0-045 M barbitone buffer pH 8-6. The agar was will exhibit a spectrum of mobility, moving as a poured on to a glass plate (8 x 8 cm) to give a depth broad band on electrophoresis and producing a of agar of 1-7 mm. The pattern of sample wells and pattern of smooth arcs with monospecific antisera antiserum troughs was cut as required. Electro- to IgG, IgA, and IgM. A single clone of plasma phoresis of sera was carried out in an electrophoresis cells synthesises immunoglobulin of one molecular tank (Shandon Southern Limited) containing type only. A number of such molecules possessing 0045 M barbitone buffer pH 8-6 at a current of on September 29, 2021 by guest. Protected copyright. identical charge will travel as a discrete band on approximately 20 mA per plate for 45 minutes. The electrophoresis, producing characteristic distortion troughs were then filled with the relevant antisera of the polyclonal arc on visualisation with specific and the plates incubated at room temperature antisera. overnight. The diagnosis of a monoclonal immunoglobulin In this laboratory, a mixture of three monospecific is suggested by serum protein electrophoresis on antisera (anti-IgG, anti-IgA, and anti-IgM) is cellulose acetate, agarose, or some other support employed. These antisera were raised in sheep and medium. Its verification requires visual interpretation absorbed where necessary to render them mono- of precipitation patterns on IEP. If only a small specific. Antisera to kappa or lambda light chains amount of monoclonal protein is present, there may were obtained from Kallestadt Laboratories. be insufficient distortion of the polyclonal arc to IEP in agarose was carried out using the Corning- allow identification of the monoclonal protein, ACI agarose film cassette system. This system particularly in the presence of a polyclonal increase includes pre-poured gel plates of 1 % agarose in of the same immunoglobulin class, and a faint 0-065 M barbital buffer, containing 0-035 % disodium gamma band seen on cellulose acetate electro- EDTA pH 8 6 and 50 g/l sucrose. The pre-formed plates contain wells for the addition of test serum and troughs for the addition of antisera after Received for publication 3 September 1979 electrophoresis. Electrophoresis is carried out in 500 J Clin Pathol: first published as 10.1136/jcp.33.5.500 on 1 May 1980. Downloaded from A Hpp iation wel "' Serum .iiiill' P utients seru m NdrmaI Cathode Anode AniIgG Normal Normal k :A serum Test AkapaAntichain _ _ = X {~~~~~~~ightchain Test C Normal Anti lambda light chain 0 Test Serum Test _... =4. Anti whole Nlormal human serum Fig. I Putient 1: Anti lgG (a) Electrophopre.si.s Test of serum in agartose. http://jcp.bmj.com/ (b) Ininuno- electrophoresis of .serum in cigar. (c) Inmmuno- Anti IgA electrophoresis of' Normat .serumn in Jgar-ose. on September 29, 2021 by guest. Protected copyright. Anti IgM Test Anti kappa Normal light chain Anti lambdda Test light chain Anti IgG, Normtl IgA, IgM J Clin Pathol: first published as 10.1136/jcp.33.5.500 on 1 May 1980. Downloaded from 2D Application wel Serum Patients Normal serum .:.=....... Cathode Anode Test z~~~~~~~~~A;'tLIgG Normal Normal serum ~Anti kappa Test light chain Normal *_4 "1111kAnti lambda Te = _ light chain Serum Test IX ............ Anti whole Normal ; human serum Anti IgO Test http://jcp.bmj.com/ ..- ... Fig. 2 Patient 7: (a) Electrop/wresis Normal Anhi IgA of serum in agarose. (b) Immuzno- electrophlresis of serum in cigar. (c) Iuniuno- A nti 1g M electroplmresis of on September 29, 2021 by guest. Protected copyright. serum in agcarose. Test Anti kappa Normal light chain Anti lambda -light chain Test Anti IgG. *^kt>*- <- ^IgA. Ig M Normal J Clin Pathol: first published as 10.1136/jcp.33.5.500 on 1 May 1980. Downloaded from Detection ofmonoclonal immunoglobulins by immunoelectrophoresis; a possible source oferror 503 barbital buffer 005 M containing 0.035% EDTA Discussion at pH 8-6. The cassette system comprises an electro- phoresis tank and pre-set power supply, the time All five sera cited in this report contained a mono- for an electrophoretic run being 30-40 minutes. clonal IgG on IEP in agarose, which were difficult After electrophoresis and the addition of antisera to visualise by IEP in agar. None of the patients the plates are incubated overnight. The antisera had multiple myelomata as defined by accepted usually employed are provided by Corning Medical criteria:2 all were probable examples of 'monoclonal as part of the above system and were found on gammopathy'. It is well recognised that paraproteins testing to be monospecific for the stated antigen. may be detected in as many as 3 % of patients aged The precipitation lines so formed may be enhanced over 70 years.3 by staining with Amido Black. The increasing use of cellulose acetate electro- phoresis to screen serum samples undergoing Results biochemical or immunological investigations has led to the frequent accidental detection of many Figures 1 and 2 show comparisons of electro- asymptomatic monoclonal proteins. phoresis and immunoelectrophoresis of two of the Occasionally difficulty is found in the definitive five sera in agar and agarose. In all cases the mono- identification of the nature of this monoclonal band. clonal protein in question is the IgG class. The Positive identification of the immunoglobulin class results for IEP in agar show only the anti-IgG and involved is important in the long-term follow-up of anti-light chain plates. The Corning agarose system such patients since serum paraproteins may be employs a battery of antisera, and the full results detected many years before clinical presentation with have been shown. malignant immunocytoma. Also, in patients receiv- In each case diagnosis of the monoclonal IgG ing chemotherapy for myeloma, assessment of the was difficult on the agar plates, but in the agarose tumour size by serum paraprotein studies allows system, the presence of a monoclonal IgG was quite important monitoring during treatment. It is obvious. Relevant laboratory details for each of the important, therefore, to establish that the apparent five cases are shown in the Table. IEP in agarose failure to detect a monoclonal protein on IEP is not has also been of value in the confirmation of the an artefact due to the use of an inappropriate presence of monoclonal IgM in sera. support medium. We have shown that, in some of Since the purpose of this study was to show a these cases, the use of a different gel allows positive variation in results using different media, it was identification of the immunoglobulin class of the http://jcp.bmj.com/ necessary to use the same antisera for both methods. paraprotein. The antisera usually employed in this laboratory were used in the Corning system in place of the References Corning antisera. (A previous comparison of our Grabar P, Williams CA. Methode permettant l'etude in-house antisera and the Corning antisera had, in conjugee des proprietes electrophoretiques et im- fact, shown identical results.) Preincubation of the munochimiques d'un melange de prot6ines. Applica- test sera with agar or agarose did not affect the tion au serum sanguin. Biochem Biophys Acta on September 29, 2021 by guest. Protected copyright. mobility of the monoclonal immunoglobulin. 1953;10:193-4. Table Laboratory details offive cases Case AgelSex Band on IEP findings in Immunoglobulin levels (g/litre) cellulose acetate electrophoresis Agar Agarose IgG IgA IgM 1 85 M Normal Monoclonal 8.45 1 90 1-40 IgG (A) 2 98 F y Normal Monoclonal 12-55 3.55 0 65 IgG (A) 3 73 F y Normal Monoclonal 14-40 2.65 050 IgG (K) 4 69 F y Equivocal Monoclonal 19-40 5.40 1-40 IgG (A) 5 84 M y Equivocal Monoclonal 7-15 2 85 1-30 IgG (K) J Clin Pathol: first published as 10.1136/jcp.33.5.500 on 1 May 1980.