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Basic science
Original research
Development of a novel magnetic particle-based agglutination immunoassay for anticardiolipin antibody detection in syphilis
  1. Mayur R Shukla1,
  2. John W Deutsch2,
  3. Lara E Pereira1,
  4. Ellen N Kersh1,
  5. Yetunde F Fakile1
  1. 1 Division of STD Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
  2. 2 Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee, USA
  1. Correspondence to Dr Mayur R Shukla, Division of STD Prevention, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA; iun9{at}cdc.gov

Abstract

Objectives Serological tests of non-treponemal and treponemal types are the most frequently used for syphilis diagnosis. Treponemal tests are available in wide variety of assay formats; however, limited advances have been made for the improvement of conventional non-treponemal tests. The objective of this work was to develop a novel non-treponemal magnetic particle-based agglutination assay (NT-MAA) and evaluate its feasibility for syphilis testing.

Methods Cardiolipin was modified and coupled to magnetic microbeads. Serum diluted in phosphate-buffered saline was mixed with cardiolipin-coupled beads and incubated in a round bottom microplate for 90–120 min followed by visual inspection. A panel of reported syphilis (n=127) and non-reactive (n=244) specimens was prepared to evaluate the NT-MAA performance in comparison to conventional rapid plasma reagin (RPR). Treponema pallidum particle agglutination (TP-PA) assay and enzyme immunoassay (EIA) were included. Analytical sensitivity and reproducibility of NT-MAA were also determined.

Results The non-treponemal NT-MAA and RPR showed sensitivity of 90.6% and 88.2% and specificity of 96.7% and 100%, respectively. The treponemal TP-PA and EIA yielded sensitivity of 100% and 99.2%, respectively, and 100% specificity by both assays. The per cent agreement between NT-MAA and RPR was 97% (kappa=0.931, 95% CI 0.891 to 0.971). Analytical sensitivity determined with IgM anticardiolipin antibody (ACA) was 2.6 µg/mL for both NT-MAA and RPR, while IgG ACA yielded 0.9 µg/mL and 1.7 µg/mL for NT-MAA and RPR, respectively. Qualitative results of intra-assay and interassay reproducibility revealed 100% consistency for NT-MAA.

Conclusion Preliminary evaluation of the novel NT-MAA validated proof of concept using laboratory-characterised syphilis sera and demonstrated performance comparable to RPR. Further validation of NT-MAA using additional specimens with better clinical staging may broaden the scope of developed test for syphilis diagnosis.

  • syphilis
  • diagnostics
  • immunology
  • testing
  • antibodies
http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/sextrans-2020-054437

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    Footnotes

    • Handling editor Federico Garcia

    • Contributors MRS and JWD participated in test concept design, specimen testing, validation and data analysis. All authors contributed equally for writing this manuscript. All authors read and approved the final manuscript.

    • Funding The study was funded by the CDC (Atlanta, Georgia, USA).

    • Disclaimer The opinions, interpretations and conclusions in this study are those of the author(s) and are not necessarily endorsed by the CDC. The use of trade names is for identification purposes only and does not constitute endorsement by the CDC or the US Department of Health and Human Services.

    • Competing interests None declared.

    • Patient consent for publication Not required.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.