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Köppert S, Wolf C, Becza N, Sautto GA, Franke F, Kuerten S, Ross TM, Lehmann PV, Kirchenbaum GA. Affinity Tag Coating Enables Reliable Detection of Antigen-Specific B Cells in Immunospot Assays. Cells 2021; 10:cells10081843. [PMID: 34440612 PMCID: PMC8394687 DOI: 10.3390/cells10081843] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 07/09/2021] [Accepted: 07/16/2021] [Indexed: 11/26/2022] Open
Abstract
Assessment of humoral immunity to SARS-CoV-2 and other infectious agents is typically restricted to detecting antigen-specific antibodies in the serum. Rarely does immune monitoring entail assessment of the memory B-cell compartment itself, although it is these cells that engage in secondary antibody responses capable of mediating immune protection when pre-existing antibodies fail to prevent re-infection. There are few techniques that are capable of detecting rare antigen-specific B cells while also providing information regarding their relative abundance, class/subclass usage and functional affinity. In theory, the ELISPOT/FluoroSpot (collectively ImmunoSpot) assay platform is ideally suited for antigen-specific B-cell assessments since it provides this information at single-cell resolution for individual antibody-secreting cells (ASC). Here, we tested the hypothesis that antigen-coating efficiency could be universally improved across a diverse set of viral antigens if the standard direct (non-specific, low affinity) antigen absorption to the membrane was substituted by high-affinity capture. Specifically, we report an enhancement in assay sensitivity and a reduction in required protein concentrations through the capture of recombinant proteins via their encoded hexahistidine (6XHis) affinity tag. Affinity tag antigen coating enabled detection of SARS-CoV-2 Spike receptor binding domain (RBD)-reactive ASC, and also significantly improved assay performance using additional control antigens. Collectively, establishment of a universal antigen-coating approach streamlines characterization of the memory B-cell compartment after SARS-CoV-2 infection or COVID-19 vaccinations, and facilitates high-throughput immune-monitoring efforts of large donor cohorts in general.
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Affiliation(s)
- Sebastian Köppert
- Research & Development Department, Cellular Technology Limited, Shaker Heights, OH 44122, USA; (S.K.); (C.W.); (N.B.); (F.F.); (P.V.L.)
- Institute of Anatomy and Cell Biology, Friedrich-Alexander University Erlangen-Nürnberg, 91054 Erlangen, Germany;
| | - Carla Wolf
- Research & Development Department, Cellular Technology Limited, Shaker Heights, OH 44122, USA; (S.K.); (C.W.); (N.B.); (F.F.); (P.V.L.)
- Institute of Anatomy and Cell Biology, Friedrich-Alexander University Erlangen-Nürnberg, 91054 Erlangen, Germany;
| | - Noémi Becza
- Research & Development Department, Cellular Technology Limited, Shaker Heights, OH 44122, USA; (S.K.); (C.W.); (N.B.); (F.F.); (P.V.L.)
| | - Giuseppe A. Sautto
- Center for Vaccines and Immunology, University of Georgia, Athens, GA 30602, USA; (G.A.S.); (T.M.R.)
| | - Fridolin Franke
- Research & Development Department, Cellular Technology Limited, Shaker Heights, OH 44122, USA; (S.K.); (C.W.); (N.B.); (F.F.); (P.V.L.)
| | - Stefanie Kuerten
- Institute of Anatomy and Cell Biology, Friedrich-Alexander University Erlangen-Nürnberg, 91054 Erlangen, Germany;
- Institute of Neuroanatomy, Medical Faculty, University of Bonn, 53115 Bonn, Germany
| | - Ted M. Ross
- Center for Vaccines and Immunology, University of Georgia, Athens, GA 30602, USA; (G.A.S.); (T.M.R.)
- Department of Infectious Diseases, University of Georgia, Athens, GA 30602, USA
| | - Paul V. Lehmann
- Research & Development Department, Cellular Technology Limited, Shaker Heights, OH 44122, USA; (S.K.); (C.W.); (N.B.); (F.F.); (P.V.L.)
| | - Greg A. Kirchenbaum
- Research & Development Department, Cellular Technology Limited, Shaker Heights, OH 44122, USA; (S.K.); (C.W.); (N.B.); (F.F.); (P.V.L.)
- Correspondence: ; Tel.: +1-(216)-791-5084
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Abstract
Nonspecific staining in ELISpot assay is a major obstacle in accurate quantification of experimental data. The appearance of nonspecific spots may be caused by different factors including cell- and immunoassay-related issues. In our study, we have shown that nonspecific spots can result from either cells or their debris sticking to the membranes in ELISpot plates, as well as by impurities in wash buffers and precipitation of aggregated detection antibodies. Although there is a growing interest in using Fluorospot assays allowing for simultaneous detection of multiple cell-secreted proteins, it appears that these fluorescence assays are more susceptible to developing nonspecific profiles resembling specific spots. In this chapter, we outline necessary ELISpot controls that need to be employed to tell the difference between bona fide spots vs. stained artifacts.
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