Testing Antigens, Antibodies, and Immune Cells in COVID-19 as a Public Health Topic-Experience and Outlines

Abstract

The current COVID-19 pandemic has triggered an accelerated pace in all research domains, including reliable diagnostics methodology. Molecular diagnostics of the virus and its presence in biological samples relies on the RT-PCR method, the most used and validated worldwide. Nonconventional tests with improved parameters that are in the development stages will be presented, such as droplet digital PCR or CRISPR-based assays. These molecular tests were followed by rapid antigen testing along with the development of antibody tests, whether based on ELISA platform or on a chemiluminescent microparticle immunoassay. Less-conventional methods of testing antibodies (e.g., lateral flow immunoassay) are presented as well. Left somewhere in the backstage of COVID-19 research, immune cells and, furthermore, immune memory cells, are gaining the spotlight, more so in the vaccination context. Recently, methodologies using flow-cytometry evaluate circulating immune cells in infected/recovered patients. The appearance of new virus variants has triggered a surge for tests improvement. As the pandemic has entered an ongoing or postvaccination era, all methodologies that are used to monitor public health focus on diagnostic strategies and this review points out where gaps should be filled in both clinical and research settings.

Keywords: SARS-CoV-2; detection; methodology.

Figure 1

Main molecular targets and antigens detected in SARS-Cov2 infection used in diagnosis. Created with BioRender.com. (access on 1 October 2021).

Figure 2

Generated antibody types during viral infections. (A) Neutralizing antibodies can link to the viral particle, hindering its entrance in the target cell. (B) Antibodies that can link to the specific receptor that is used by the viral particle, hindering its entrance in the target cell. (C) Low-affinity antibodies linked to the viral particle that can activate Fc-receptor on the target cell and thus favor viral entry into the cell generating ADE-related mechanisms. Created with BioRender.com. (access on 15 September 2021).

Figure 3

Cellular immune response upon infection detected using flow cytometry. Activated DCs present antigen and co-stimulatory molecules to specific naïve T cells, which become activated and further differentiate into effector cells (T CD8+ cytotoxic cells), T helper cells (CD4+). Activated DCs can directly activate specific B cells and induce B cell differentiation. T follicular helper (TFH) cells help B cells to differentiate into plasma cells that secrete specific antibodies and further generate B memory cells. Generated antibodies physically hinder the entrance of new viral particles into cells. Memory T cells are generated to sustain the long-time cellular immune memory, and CD4+ T cells memory cells secrete cytokines that induce the cytotoxic activity of T cells CD8+ that attack infected cells, stopping the further viral reproduction. T and B memory cells sustain long-lasting memory of the infection, and upon a second encounter with the same virus, quickly trigger all the necessary immune pathways. Created with BioRender.com. (access on 15 September 2021).