In vitro, classical complement activation differs by disease severity and between SARS-CoV-2 antigens (preprint)

Antibodies specific for the spike glycoprotein (S) and nucleocapsid (N) SARS-CoV-2 proteins are typically present during severe COVID-19, and induced to S after vaccination. The binding of viral antigens by antibody can initiate the classical complement pathway. Since complement could play pathological or protective roles at distinct times during SARS-CoV-2 infection we determined levels of antibody-dependent complement activation along the complement cascade. Here, we used an ELISA assay to assess complement protein binding (C1q) and the deposition of C4b, C3b, and C5b to S and N antigens in the presence of anti-SARS-CoV-2 antibodies from different test groups: non-infected, single and double vaccinees, non-hospitalised convalescent (NHC) COVID-19 patients and convalescent hospitalised (ITU-CONV) COVID-19 patients. C1q binding correlates strongly with antibody responses, especially IgG1 levels. However, detection of downstream complement components, C4b, C3b and C5b shows some variability associated with the antigen and subjects studied. In the ITU-CONV, detection of C3b-C5b to S was observed consistently, but this was not the case in the NHC group. This is in contrast to responses to N, where median levels of complement deposition did not differ between the NHC and ITU-CONV groups. Moreover, for S but not N, downstream complement components were only detected in sera with higher IgG1 levels. Therefore, the classical pathway is activated by antibodies to multiple SARS-CoV-2 antigens, but the downstream effects of this activation may differ depending on the specific antigen targeted and the disease status of the subject. O_LISpike- and nucleocapsid-specific antibodies activate complement in vitro C_LIO_LIC1q binding correlates with IgG1 antibody levels C_LIO_LIGeneration of C4b, C3b and C5b relates to the antigen targeted and the patient group tested C_LI

Longitudinal protection following natural SARS-CoV-2 infection and early vaccine responses: insights from a cohort of community based dental health care professionals (preprint)

Abstract Background The threshold of protection for anti-SARS-CoV-2 spike glycoprotein antibodies and their longevity are not known. Interpretation of serological results in with respect to international reference material can inform this essential question. Methods 1,507 West Midlands dental care professionals were recruited into this study in June 2020. Baseline seroprevalence of antibodies directed against the SARS-CoV-2 spike glycoprotein was determined and the cohort was followed longitudinally for 6 months until January/February 2021 through the second wave of the COVID-19 pandemic in the United Kingdom, and commencement of vaccination. Results Baseline seroprevalence was 16.3% in this cohort, compared to estimates in the general population of between 6-7%. Seropositivity was retained in over 70% of participants at 3 and 6-month follow up and conferred a 74% reduced risk of infection. During follow-up, no PCR-proven infections occurred in individuals with a baseline anti-SARS-CoV-2 IgG level greater than 147.6 IU/ml with respect to the World Health Organization international standard 20-136. Post-vaccination, antibody responses were more rapid and of higher magnitude in individuals with who were seropositive at baseline. Conclusion Natural infection leads to a serological response that remains detectable in over 70% of individuals 6 months after initial sampling and 9 months from the peak of the first wave of the pandemic. This response is associated with protection from future infection. Even if serological responses wane, a single dose of the Pfizer-BioNTech vaccine is associated with an antibody response indicative of immunological memory. Funding The Association of Clinical Biochemistry and Laboratory Medicine and The Institute for Global Innovation (IGI) of the University of Birmingham.