anti-idiotype antibodies for the diagnosis of...

LCDC REPORT

Anti-idiotype antibodies for the diagnosis of infectious diseases

BERNARD R BRODEUR, PHD, JOSEE HAMEL, PHD, EILLEEN TACKABERRY, MSC

IMMUNOASSAYS ARE WELL-ESTABLISHED AS PRACTICAL.

rapid tests for detecting many infectious agents in the clinical laboratory. Immunoassays for infectious pathogens include the traditional radioimmunoassay and the more recent enzyme-linked immunosorbent assay (ELISA). which allows numerou s different configurations of antigen and antibody. Most immuneassays use primary antibodies (either polyclonal or monoclonal) directed against specific epitopes of the infectious agent; the amount of primary a ntibody bound via a second antibody subsequently is quantitated by tagging with an easily identifia ble ma rker. Despite tl1e general success of this a pproach . effective in1munoassays for certain infectious agents have been very d ifficult to develop, prompting investigators to search for a lternatives in the design of rapid immunological tests.

A recent strategy taken by the a utl1ors ' laboratory has exploited llie idiotype network of the immune system to develop novel reagents for improved detection of microbia l antigens. The highly specific antibodies generated during an immune response contain combining s ites with structural complementarity to th e epitope of the target antigen. The hypervariable region of the immunoglobulin molecule, which forms the antibodycombining site and is responsible for defining the specificity of tl1e antibody, also carries a unique set of antigen ic determinants, which collectively a re termed the idiotype of that antibody. These idiotypic determinants are antigenic , and as such may stimula te the formation of anti-idiotype antibodies (Figure 1). Studies from many laboratories h ave confirmed that the combining s ite of some of the anti -idiotype antibodies func-

National Laboratory for Immunology. Laboratory Centre for Disease Control. Health and Welfare Canada, Ottawa

Correspondence: Dr BR B rodeur. Chief National Laboratory for Immunology. Laboratory Centre for Disease Control. Health Protection Building. Room 18 1. Tunney·s Pasture. Ottawa. Ontario KIA OL2. Te lephone (613) 957-0179. Fax (613) 941 -9020

CAN J INFECT D IS VOL 3 No 6 N OVEMBER/DECEMBER 1992

tionally will mimic the conforma tion of tl1e original epitope . representing its ·internal image' (1-5). These pa rticula r a nti -idiotype a ntibodies . tl1us . can substitute for U1 e antigen in primary antibody binding.

Much of tl1e evidence for tl1e ability of anti-idiotype antibodies to act as s urrogate antigens has been provided by research into tl1e development of a nti idiotype vaccines. In recent years . anti -idiotype a nti bodies h ave been used to immunize e:>..lJerimental anin1als against a variety of viruses. bacteria and parasites (6.7). The anti-anti-idiotype response induced in tl1e hosts against llie nomina l paU1ogen has included development of protective immunity (eg. for hepatitis B virus. Streptococcus pneumoniae and Trypanosoma

rlwdesiense). production of viral neutralizing antibodies (eg. for poliovirus type II a nd rabies virus) and s timula tion of cell-mediated immunity (eg. for Sendai virus and reovirus type 3).

Observations such as t hese have not only demonstrated U1e vaccine potential of a nti -idiotype a ntibodies. but also suggested that U1 ey might be u seful tools for improved immunodetection of infectious agents. As for otl1er immunoassays. tl1e particular details of any protocol may be varied considerably. But tl1e essence of an a nti -idiotype immunoassay lies in the structural s imila ri ty between llie anti-idiotype and tl1e target epitope fo r tl1e primary antibody, such that on e may substitute for the ot11er in binding to tl1at a ntibody. An example of a n anti-idiotype assay is sh own in Figure 2.

In a n inhibition assay. when antigen (present in the test sample) is a llowed to bind to a specific a ntibody. s ubsequent interaction between the antibody and complem entary anti-idiotype antibody will be blocked (compared willi a control in which no antigen is present). The inhibition of binding between idiotype and a nti idiotype can be quantitated . and will refl ect tl1e concentration of antigen present in the test sample. Alternatively. competitive immunoassays could be establish ed, willi labelled anti -idiotype a ntibodies competing with a ntigen for binding to a s pecific antibody.

319

l CDC Report

to/ - ~ - ~ microbial primary anti-idiotype antigen antibody antibody

Figure 1) ldiotypes a nd a nti-idiotypes. Antigen induces the fonnation of primary specific a nt ibody . which bears an idiotype with complementarity to the microbia l epitope. S ince the idiotypic detenninants are antigenic. the anti-idiotype antibodiesfonned against this primary antibody may mimic the structure of the original epitope

Given th e variety of existing immunoassays for infectiou agen ts. what advantages migh t be expected from an li- idiotype assays? First. there are many complex microbia l an tigens which a re d iffi cult to obta in in pu rifi ed form; by gen era ting an ti -idiotype antibodies. purified protein subs ti tu tes for th ese an tigens can be used. Second. certain antigens may have few exposed epitopes to any particular an tibody; thus. sandwich immunoassays - \.vhich require a minim u m of two accessible bindin g s ites - are n ot s u ccessful. Third . in ce rtain configurations s uch as competitive ass ays , it may be possible to achieve greater sen s itivi ty u s ing a n ti-idiotype antibod ies tha n otherwise is possible .

As a model system to te t the feasibility of this concept. Brodeu r et al recently developed an anti idiotype ELISA for human cytomegalovirus (HCMV) . HCMV is a s low growing virus . a nd curren t immuneassays for the virus in the clinical la boratory a re n ot ideal. The a uthors used a highly neu tralizin g anli HCMV a n tibody (CMVBl) and generated monoclonal anti-idiotype antibodies agains t it. Th e an ti -idiotype antibodies exhibited properties tl1at indicated they were ideal candidates for assay development: in pa r ticu la r. they completely inhibited tl1e reactivity of CMVB 1

towards its viral antigen (8). The anti -idiotype inhibition ELISA was developed with a la bora tOiy s tra in of HCMV. following the s trategy outl in ed in Figure 2 . The assay was able to detect HCMV a nd measured viral a n tigen in a dose-dependen t mann er over a clinically relevant range (20 to 0.6x l 03 pla que form ing uni ts per millili tre of urine). Th ese en couraging result have prompted tl1e authors· fu rther evalu a tion of tl1e assay wi th clin ical specimens.

Th ere is widespread interest in idiotypes and anti idiotypes for their role in regula ting the immune respon se. as probes for various cellula r receptors and a pos ible vaccines agains t tumours a nd infectious agen ts. Anti- idiotype antibodies as potential reagen ts fo r in vitro immunoassays can n ow be added to tl1is list. To the curren t workers· knowledge. n o other repor ts in the scien tific li terature h ave investigated tl1e a ppli cabil ity of tl1is idea. Non etheless. it em s likely U1 a t

320

A. Test Sample B. Control

Figure 2 ) Illustration of an a nt i-idiotype inhib it ion immunoassay. Microtitre wells a re coated w ith anti-idiotype antibodies. A Antigen is a llowed to interact w ith p rimary a ntibody a nd w ill b loclc subsequent binding of the antibody to the immobilized anti-idiotype. Inhibit ion of binding is quantitated by measuring the amount of tagged a ntibody present in the test wells versus control wells. B No antigen is p resent

an ti -idiotype antibodies a r e poised to ta ke tl1eir place among other immunological reagen ts as a valua ble option in the des ign of fu ture immunodiagnostics for infectiou s agents .

ACKNOWLEDGEMENT: Eilleen Tackaberry. a PhD stu den t in U1e Depar tm en t of Microbiology and Immunology. Universi ty of Ottawa. is supported by a Studen tship Award from the Medical Research Council of Canada.

REFERENCES I . Nisonoff A. ldiotypes: Con cepts and applica tion s.

J lmmunol199 1: 147:2429-38. 2. Kohler H. Kaveri S. Kieber -Emmon s T. Morrow WJW.

Muller S. Raychaudhuri S. ldiotypic networks and nature of m olecular mimicry: An overv iew. In: Abelson J N. Simon MI. eels. Methods in Enzymology: Antibodies. Antigen s. and Molecular Mimicry. vol 178. San Diego: Academic Press. 1989:3-35.

3. Hamel J . Brodeur BR. Induction of an immune response to Ule porin of H injluenzae type b by mon oclonal antiicliotypic an tibodies . Microb Pathogenesis 1990:9:81-93.

4. Brodeu r BR. Fauch er S, O'Shaughnessy MY. Hamel J. Mon oclonal idiotypic and an ti -id iolypic an tibodies to human immunodeficiency virus type 1 envelope glycoprotein. J Gen Virol 199 1:72 :5 1-8 .

5. Wiley J A. Hamel J. Brodeur BR. Monoclon al anti- idiotypes induce n eut:ralizing antibodies to En lerovirus-70 conformational ep i topes. J V irol 1992:66:5744-5 1.

6. Hiem aux JR. lcliotypic vaccines and infectiou s diseases. In fect lmmu n 1988:56 :1407- 13.

7. Finberg RW. Ertl H . The u se of an ti -idiotypic an tibodies as vaccines against infectiou agents. CRC Critical Rev lmmunoll987:7:269-84.

8. Tackberry ES. Han1el J. La ro e Y. Kuhl R. Brodeu r BR. Monoclonal an ti- id iotypes for Ule rapid detection of human cytom egalovirus. J Virol Melil 1992 (In press)

CAN J INFECT D IS VOL 3 N o 6 N OVEMBER/DECEMBER 1992

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