AUTHOR=Makatsa Mohau S. , Tincho Marius B. , Wendoh Jerome M. , Ismail Sherazaan D. , Nesamari Rofhiwa , Pera Francisco , de Beer Scott , David Anura , Jugwanth Sarika , Gededzha Maemu P. , Mampeule Nakampe , Sanne Ian , Stevens Wendy , Scott Lesley , Blackburn Jonathan , Mayne Elizabeth S. , Keeton Roanne S. , Burgers Wendy A. 

TITLE=SARS-CoV-2 Antigens Expressed in Plants Detect Antibody Responses in COVID-19 Patients

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.589940

DOI=10.3389/fpls.2021.589940

ISSN=1664-462X

ABSTRACT=<p><bold>Background</bold>: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has swept the world and poses a significant global threat to lives and livelihoods, with 115 million confirmed cases and at least 2.5 million deaths from Coronavirus disease 2019 (COVID-19) in the first year of the pandemic. Developing tools to measure seroprevalence and understand protective immunity to SARS-CoV-2 is a priority. We aimed to develop a serological assay using plant-derived recombinant viral proteins, which represent important tools in less-resourced settings.</p><p><bold>Methods</bold>: We established an indirect ELISA using the S1 and receptor-binding domain (RBD) portions of the spike protein from SARS-CoV-2, expressed in <italic>Nicotiana benthamiana</italic>. We measured antibody responses in sera from South African patients (<italic>n</italic> = 77) who had tested positive by PCR for SARS-CoV-2. Samples were taken a median of 6 weeks after the diagnosis, and the majority of participants had mild and moderate COVID-19 disease. In addition, we tested the reactivity of pre-pandemic plasma (<italic>n</italic> = 58) and compared the performance of our in-house ELISA with a commercial assay. We also determined whether our assay could detect SARS-CoV-2-specific IgG and IgA in saliva.</p><p><bold>Results:</bold> We demonstrate that SARS-CoV-2-specific immunoglobulins are readily detectable using recombinant plant-derived viral proteins, in patients who tested positive for SARS-CoV-2 by PCR. Reactivity to S1 and RBD was detected in 51 (66%) and 48 (62%) of participants, respectively. Notably, we detected 100% of samples identified as having S1-specific antibodies by a validated, high sensitivity commercial ELISA, and optical density (OD) values were strongly and significantly correlated between the two assays. For the pre-pandemic plasma, 1/58 (1.7%) of samples were positive, indicating a high specificity for SARS-CoV-2 in our ELISA. SARS-CoV-2-specific IgG correlated significantly with IgA and IgM responses. Endpoint titers of S1- and RBD-specific immunoglobulins ranged from 1:50 to 1:3,200. S1-specific IgG and IgA were found in saliva samples from convalescent volunteers.</p><p><bold>Conclusion</bold>: We demonstrate that recombinant SARS-CoV-2 proteins produced in plants enable robust detection of SARS-CoV-2 humoral responses. This assay can be used for seroepidemiological studies and to measure the strength and durability of antibody responses to SARS-CoV-2 in infected patients in our setting.</p>