Modulation of porcine alphacoronavirus pathogenesis by antibodies to SARS-CoV-2

BACKGROUND: A variety of antibodies against the SARS-CoV-2 with different functional activities can lead to immune pathology and/or modulation of infection due to antibody-dependent enhancement. An important role in the development of ADE, as exemplified by Dengue fever, is played by low-affinity antibodies, which interacting with the virus, do not neutralize it, but on the contrary forms the virus-antibody complex to immune cells (monocytes/macrophages, B-cells). There are conflicting data on the antibody-dependent enhancement presence in COVID-19 coronavirus infection. Some studies indicate a relationship between the severity of infection in patients infected by SARS-СoV-2 and the level of antibodies to closely related coronaviruses.

AIM: The aim of the study was to understand the possibility of interaction between antibodies to SARS-CoV-2 with closely related porcine coronavirus (alphacoronavirus) and their ability to modulate the development of infection in vitro.

MATERIALS AND METHODS: In the study serums and leukocytes from patients, who are convalescent after COVID-19 infection in 2020, was used. Antibody titers (IgG/IgM) was checked by commercial kit (VektorBest, Russia), based on ELISA method. In the eukaryotic expression system — Chinese hamster ovary cells, monoclonal antibody to SARS-CoV-2 spike protein and its Fab version without Fc domain were obtained. As a model, swine alphacoronavirus- transmissible gastroenteritis virus (TGEV) was used. Replication activity of TGEV was studied in porcine leukocyte cell culture. The ability of this virusto induce the interferon gamma synthesis in leukocytes from convalescents was assessed TigraTest SARS-CoV-2 Enzyme-Linked SPOT analysis (Russia). Virus titration and neutralization assay with sera and monoclonal antibodies were carried out in porcine kidney PK-15 cell line.

RESULTS: Serum samples from 43 donors (59% female, 41% male) aged from 21 to 56 was studied for the presence of class M and G antibodies to SARS-CoV-2 by ELISA method. Class M antibodies were found in only one donor. The highest titers of class G antibodies (>1:400 to >1:1600) were detected among donors 40–50 years old. For four donors with the highest antibody titers, HLA-II type was determined. The DQA1 allele in 3 patients was found to have the *0501 variant, which, according to literature data, is associated with autoimmune thyroid diseases. For the DQB1 allele, two convalescents had exactly the same variants (*0602-8). Among HLA DRB1, all patients had different allele variants (*09, *11, *01,*03,*13,*15,*08,*13).

Among the samples, studied by ELISPOT method, in 45,5% of samples a positive T-cell response was noted after stimulation of macrophages with the S peptides of the SARS-CoV-2 protein and in 22.7% of samples in response to the pool of N peptides of the SARS-CoV-2 protein. Interestingly, infection of macrophages from convalescents with the transmissible gastroenteritis virus caused interferon-gamma expression in 31,8% of cases.

The monoclonal antibody to the Spike protein SARS-CoV-2 and its Fab variant were not able to neutralize the TGEV. Interestingly, serum samples from 16 donor’s convalescent after COVID-19 caused virus neutralization in PK-15 cell culture at dilutions of 1:4-1:8.

CONCLUSIONS: We have shown that porcine alphacoronavirus induces (in 31.8% of cases) the synthesis of interferon gamma in macrophages of recovered afterCOVID-19 donors, which may indicate cross-recognition of the antigen of a closely related coronavirus. However, monoclonal antibodies against the Spike protein SARS-CoV-2 did not demonstrate to TGEV neutralization. In turn, the neutralization of the TGEV by sera from recovered COVID-19 donors suggests that not only Spike protein, but also other coronavirus antigens can play a significant role in antigenic imprinting and antibody-dependent enhancement of COVID-19.