Factors influencing the immune response over 15 months after SARS-CoV-2 infection: A longitudinal population-wide study in the Faroe Islands.

BACKGROUND: The durability of SARS-CoV-2 antibody response and the resulting immunity to COVID-19 is unclear. OBJECTIVES: To investigate long-term humoral immunity to SARS-CoV-2. METHODS: In this nationwide, longitudinal study, we determined antibody response in 411 patients aged 0-93 years from two waves of infections (March to December 2020) contributing 1063 blood samples. Each individual had blood drawn on 4-5 occasions 1-15 months after disease onset. We measured total anti-SARS-CoV-2 receptor-binding domain (RBD) antibody using a qualitative RBD sandwich ELISA, IgM, IgG and IgA levels using an quantitative in-house ELISA-based assay  and neutralizing antibodies (NAbs) using an in-house ELISA-based pseudoneutralizing assay. IgG subclasses were analyzed in a subset of samples by ELISA-based assay. We used nonlinear models to study the durability of SARS-CoV-2 antibody responses and its influence over time. RESULTS: After 15 months, 94% still had detectable circulating antibodies, mainly the IgG isotype, and 92% had detectable NAbs. The distribution of IgG antibodies varied significantly over time, characterized by a biphasic pattern with an initial decline followed by a plateau after approximately 7 months. However, the NAbs remained relatively stable throughout the period. The strength of the antibody response was influenced by smoking and hospitalization, with lower IgG levels in smokers and higher levels in hospitalized individuals. Antibody stability over time was mainly associated with male sex and older age with higher initial levels but more marked decrease. CONCLUSIONS: The humoral immune response to SARS-CoV-2 infection varies depending on behavioral factors and disease severity, and antibody stability over 15 months was associated with sex and age.

Humoral and cellular immune responses after three or four doses of BNT162b2 in patients with hematological malignancies.

OBJECTIVES: Initial responses to coronavirus disease 2019 vaccination are impaired in patients with hematological malignancies. We investigated immune responses after three or four doses of BNT162b2 in patients with myeloid and lymphoid malignancies compared to controls, and identified risk factors for humoral and cellular nonresponse 1 year after first vaccination. METHODS: In 407 hematological patients (45 myeloid, 362 lymphoid) and 98 matched controls, we measured immunoglobulin G (IgG) and neutralizing antibodies specific for the receptor-binding domain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at baseline, 3 weeks, 2, 6, and 12 months, and interferon-γ release at 12 months. RESULTS: In patients with lymphoid malignancies, SARS-CoV-2 receptor-binding domain IgG concentration and mean neutralizing capacity was lower than in controls at all time points. A diagnosis of chronic lymphocytic B-cell leukemia (CLL) or lymphoma was associated with humoral nonresponse at 12 months compared to having multiple myeloma/amyloidosis (p < .001 and p = .013). Compared to controls, patients with lymphoid malignancies had increased risk of cellular nonresponse. A lymphoma diagnosis was associated with lower risk of cellular nonresponse compared to patients with multiple myeloma/amyloidosis, while patients with CLL had comparable response rates to patients with multiple myeloma/amyloidosis (p = .037 and p = .280). CONCLUSIONS: In conclusion, long-term humoral and cellular immune responses to BNT162b2 were impaired in patients with lymphoid malignancies.

SARS-CoV-2 antibody dynamics over time and risk factors associated with infection and long COVID-19 symptoms in large working environments.

BACKGROUND: Factors influencing SARS-CoV-2 antibody dynamics, transmission, waning and long COVID-19 symptomatology are still not fully understood. METHODS: In the Danish section of the Novo Nordisk Group, we performed a prospective seroepidemiological study during the first and second waves of the COVID-19 pandemic. All employees and their household members (>18 years) were invited to participate in a baseline (June-August 2020), 6-month follow-up (December 2020-January 2021), and 12-month follow-up (August 2021) sampling. In total, 18,614 accepted and provided at least one blood sample and completed a questionnaire regarding socioeconomic background, health status, previous SARS-CoV-2 infection, and persistent symptoms. Total antibody and specific IgM, IgG and IgA levels against recombinant receptor binding domain were tested. RESULTS: At baseline, the SARS-CoV-2-antibody seroprevalence was 3.9%. At 6-month follow-up, the seroprevalence was 9.1%, while at 12-month follow-up, the seroprevalence was 94.4% (after the vaccine roll-out). Male sex and younger age (18-40 years) were significant risk factors for seropositivity. From baseline to the 6-month sampling, we observed a substantial waning of IgM, IgG and IgA levels (p < 0.001), regardless of age, sex and initial antibody level. An increased antibody level was found in individuals infected prior to vaccination compared to vaccinated infection naïves (p < 0.0001). Approximately a third of the seropositive individuals reported one or more persistent COVID-19 symptoms, with anosmia and/or ageusia (17.5%) and fatigue (15.3%) being the most prevalent. CONCLUSION: The study provides a comprehensive insight into SARS-CoV-2 antibody seroprevalence following infection and vaccination, waning, persistent COVID-19 symptomatology and risk factors for seropositivity in large working environments.

Short-Lived Antibody-Mediated Saliva Immunity against SARS-CoV-2 after Vaccination.

Knowledge about the effect of vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on immunity reflected in the saliva is sparse. We examined the antibody response in saliva compared to that in serum 2 and 6 months after the first vaccination with the BNT162b2 vaccine. Four hundred fifty-nine health care professionals were included in a prospective observational study measuring antibody levels in saliva and corresponding serum samples at 2 and 6 months after BNT162b2 vaccination. Vaccinated, previously SARS-CoV-2-infected individuals (hybrid immunity) had higher IgG levels in saliva at 2 months than vaccinated, infection-naive individuals (P < 0.001). After 6 months, saliva IgG levels declined in both groups (P < 0.001), with no difference between groups (P = 0.37). Furthermore, serum IgG levels declined from 2 to 6 months in both groups (P < 0.001). IgG antibodies in saliva and serum correlated in individuals with hybrid immunity at 2 and 6 months (ρ = 0.58, P = 0.001, and ρ = 0.53, P = 0.052, respectively). In vaccinated, infection-naive individuals, a correlation was observed at 2 months (ρ = 0.42, P < 0.001) but not after 6 months (ρ = 0.14, P = 0.055). IgA and IgM antibodies were hardly detectable in saliva at any time point, regardless of previous infection. In serum, IgA was detected at 2 months in previously infected individuals. BNT162b2 vaccination induced a detectable IgG anti-SARS-CoV-2 RBD response in saliva at both 2 and 6 months after vaccination, being more prominent in previously infected than infection-naive individuals. However, a significant decrease in salivary IgG was observed after 6 months, suggesting a rapid decline in antibody-mediated saliva immunity against SARS-CoV-2, after both infection and systemic vaccination. IMPORTANCE Knowledge about the persistence of salivary immunity after SARS-CoV-2 vaccination is limited, and information on this topic could prove important for vaccine strategy and development. We hypothesized that salivary immunity would wane rapidly after vaccination. We measured anti-SARS-CoV-2 IgG, IgA, and IgM concentrations in saliva and serum in both previously infected and infection-naive individuals, 2 and 6 months after first vaccination with BNT162b2, in 459 hospital employees from Copenhagen University Hospital. We observed that IgG was the primary salivary antibody 2 months after vaccination in both previously infected and infection-naive individuals, but dropped significantly after 6 months. Neither IgA nor IgM was detectable in saliva at either time point. Findings indicate that salivary immunity against SARS-CoV-2 rapidly declines following vaccination in both previously infected and infection-naive individuals. We believe this study shines a light on the workings of salivary immunity after SARS-CoV-2 infection, which could prove relevant for vaccine development.

High anti-SARS-CoV-2 seroprevalence among unvaccinated mother-child pairs from a rural setting of north-eastern Tanzania during the second wave of COVID-19.

Background: The reported infection rates, and the burden of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in low- and middle-income countries, including sub-Saharan Africa, are relatively low compared to Europe and America, partly due to limited testing capabilities. Unlike many countries, in Tanzania, neither mass screening nor restrictive measures such as lockdowns have been implemented to date. The prevalence of SARS-CoV-2 infection in rural mainland Tanzania is largely unknown. Methods: Between April and October 2021, we conducted a cross-sectional study to assess anti-SARS-CoV-2 seroprevalence among mother-child pairs (n=634 children, n=518 mothers) in a rural setting of north-eastern Tanzania. Findings: We found a very high prevalence of anti-SARS-CoV-2 antibody titres with seroprevalence rates ranging from 29% among mothers and 40% among children, with a dynamic peak in seropositivity incidence at the end of July/early in August being revealed. Significant differences in age, socioeconomic status and body composition were associated with seropositivity in mothers and children. No significant associations were observed between seropositivity and comorbidities, including anaemia, diabetes, malaria, and HIV. Interpretations: The SARS-CoV-2 transmission in a rural region of Tanzania during 2021 was high, indicating a much higher infection rate in rural Tanzania compared to that reported in the UK and USA during the same period. Ongoing immune surveillance may be vital to monitoring the burden of viral infection in rural settings without access to molecular genotyping where a load of communicable diseases may mask COVID-19. Surveillance could be implemented in tandem with the intensification of vaccination strategies.

Humoral and T-cell response 12 months after the first BNT162b2 vaccination in solid organ transplant recipients and controls: Kinetics, associated factors, and role of SARS-CoV-2 infection.

Introduction: We investigated humoral and T-cell responses within 12 months after first BNT162b2 vaccine in solid organ transplant (SOT) recipients and controls who had received at least three vaccine doses. Furthermore, we compared the immune response in participants with and without previous SARS-CoV-2 infection. Methods: We included adult liver, lung, and kidney transplant recipients, and controls were selected from a parallel cohort of healthcare workers. Results: At 12th-month, the IgG geometric mean concentrations (GMCs) (P<0.001), IgA GMCs (P=0.003), and median IFN-γ (P<0.001) were lower in SOT recipients than in controls. However, in SOT recipients and controls with previous infection, the neutralizing index was 99%, and the IgG, and IgA responses were comparable. After adjustment, female-sex (aOR: 3.6, P<0.009), kidney (aOR: 7.0, P= 0.008) or lung transplantation (aOR: 7.5, P= 0.014), and use of mycophenolate (aOR: 5.2, P=0.03) were associated with low IgG non response. Age (OR:1.4, P=0.038), time from transplantation to first vaccine (OR: 0.45, P<0.035), and previous SARS-CoV-2 infection (OR: 0.14, P<0.001), were associated with low IgA non response. Diabetes (OR:2.4, P=0.044) was associated with T-cell non response. Conclusion: In conclusion, humoral and T-cell responses were inferior in SOT recipients without previous SARS-CoV-2 infection but comparable to controls in SOT recipients with previous infection.

Humoral and T-cell response 12 months after the first BNT162b2 vaccination in solid organ transplant recipients and controls: Kinetics, associated factors, and role of SARS-CoV-2 infection

Introduction We investigated humoral and T-cell responses within 12 months after first BNT162b2 vaccine in solid organ transplant (SOT) recipients and controls who had received at least three vaccine doses. Furthermore, we compared the immune response in participants with and without previous SARS-CoV-2 infection. Methods We included adult liver, lung, and kidney transplant recipients, and controls were selected from a parallel cohort of healthcare workers. Results At 12th-month, the IgG geometric mean concentrations (GMCs) (P<0.001), IgA GMCs (P=0.003), and median IFN-γ (P<0.001) were lower in SOT recipients than in controls. However, in SOT recipients and controls with previous infection, the neutralizing index was 99%, and the IgG, and IgA responses were comparable. After adjustment, female-sex (aOR: 3.6, P<0.009), kidney (aOR: 7.0, P= 0.008) or lung transplantation (aOR: 7.5, P= 0.014), and use of mycophenolate (aOR: 5.2, P=0.03) were associated with low IgG non response. Age (OR:1.4, P=0.038), time from transplantation to first vaccine (OR: 0.45, P<0.035), and previous SARS-CoV-2 infection (OR: 0.14, P<0.001), were associated with low IgA non response. Diabetes (OR:2.4, P=0.044) was associated with T-cell non response. Conclusion In conclusion, humoral and T-cell responses were inferior in SOT recipients without previous SARS-CoV-2 infection but comparable to controls in SOT recipients with previous infection.

Waning humoral and cellular immunity after COVID-19 vaccination in patients with psoriasis treated with methotrexate and biologics: a cohort study.

BACKGROUND: mRNA-based COVID-19 vaccines have short- and long-term efficacy in healthy individuals, but their efficacy in patients with psoriasis receiving immunomodulatory therapy is less studied. OBJECTIVES: To investigate long-term immunity after COVID-19 vaccination in patients with psoriasis receiving immunomodulatory therapy. METHODS: A prospective cohort study including patients (n = 123) with psoriasis receiving methotrexate (MTX) or biologics and controls (n = 226). Only mRNA-based COVID-19 vaccines administered with standard intervals between doses were investigated. Markers of immunity included SARS-CoV-2 spike glycoprotein-specific IgG and IgA, neutralizing capacity, and interferon-γ release from T cells stimulated with peptides of the SARS-CoV-2 spike glycoprotein. RESULTS: The proportion of IgG responders was lower 6 months after vaccination in patients receiving anti-tumour necrosis factor (TNF) treatment compared with controls. Anti-TNF treatment was associated with lower IgG levels (ß = -0.82, 95% confidence interval -1.38 to -0.25; P = 0.001). The median neutralizing index was lower in the anti-TNF group [50% inhibition (interquartile range [IQR] 37-89)] compared with controls [98% inhibition (IQR 96-99)]; P < 0.001. Cellular responses were numerically lowest in the anti-TNF group. CONCLUSIONS: Treatment with anti-TNF has an impact on the immunity elicited by mRNA-based COVID-19 vaccination in patients with psoriasis, resulting in a faster waning of humoral and cellular markers of immunity; however, the clinical implications are unknown.

Lectin Pathway Enzyme MASP-2 and Downstream Complement Activation in COVID-19.

Mannose-binding lectin-associated serine protease 2 (MASP-2) is the main activator of the lectin complement pathway and has been suggested to be involved in the pathophysiology of coronavirus disease 2019 (COVID-19). To study a possible association between MASP-2 and COVID-19, we aimed at developing a sensitive and reliable MASP-2 ELISA. From an array of novel mouse-monoclonal antibodies using recombinant MASP-2 as antigen, two clones were selected to create a sandwich ELISA. Plasma samples were obtained from 216 healthy controls, 347 convalescent COVID-19 patients, and 147 prospectively followed COVID-19 patients. The assay was specific towards MASP-2 and did not recognize the truncated MASP2 splice variant MAP-2 (MAp19). The limit of quantification was shown to be 0.1 ng/mL. MASP-2 concentration was found to be stable after multiple freeze-thaw cycles. In healthy controls, the mean MASP-2 concentration was 524 ng/mL (95% CI: 496.5-551.6). No significant difference was found in the MASP-2 concentrations between COVID-19 convalescent samples and controls. However, a significant increase was observed in prospectively followed COVID-19 patients (mean: 834 ng/mL [95% CI: 765.3-902.7, p < 0.0001]). In these patients, MASP-2 concentration correlated significantly with the concentrations of the terminal complement complex (ρ = 0.3596, p < 0.0001), with the lectin pathway pattern recognition molecules ficolin-2 (ρ = 0.2906, p = 0.0004) and ficolin-3 (ρ = 0.3952, p < 0.0001) and with C-reactive protein (ρ = 0.3292, p = 0.0002). Overall, we developed a specific quantitative MASP-2 sandwich ELISA. MASP-2 correlated with complement activation and inflammatory markers in COVID-19 patients, underscoring a possible role of MASP-2 in COVID-19 pathophysiology.

Antibody responses and risk factors associated with impaired immunological outcomes following two doses of BNT162b2 COVID-19 vaccination in patients with chronic pulmonary diseases.

INTRODUCTION: Responses to COVID-19 vaccination in patients with chronic pulmonary diseases are poorly characterised. We aimed to describe humoral responses following two doses of BNT162b2 mRNA COVID-19 vaccine and identify risk factors for impaired responses. METHODS: Prospective cohort study including adults with chronic pulmonary diseases and healthcare personnel as controls (1:1). Blood was sampled at inclusion, 3 weeks, 2 and 6 months after first vaccination. We reported antibody concentrations as geometric means with 95% CI of receptor binding domain (RBD)-IgG and neutralising antibody index of inhibition of ACE-2/RBD interaction (%). A low responder was defined as neutralising index in the lowest quartile (primary outcome) or RBD-IgG <225 AU/mL plus neutralising index <25% (secondary outcome), measured at 2 months. We tested associations using Poisson regression. RESULTS: We included 593 patients and 593 controls, 75% of all had neutralising index ≥97% at 2 months. For the primary outcome, 34.7% of patients (n=157/453) and 12.9% of controls (n=46/359) were low responders (p<0.0001). For the secondary outcome, 8.6% of patients (n=39/453) and 1.4% of controls (n=5/359) were low responders (p<0.001). Risk factors associated with low responder included increasing age (per decade, adjusted risk ratio (aRR) 1.17, 95% CI 1.03 to 1.32), Charlson Comorbidity Index (per point) (aRR 1.15, 95% CI 1.05 to 1.26), use of prednisolone (aRR 2.08, 95% CI 1.55 to 2.77) and other immunosuppressives (aRR 2.21, 95% CI 1.65 to 2.97). DISCUSSION: Patients with chronic pulmonary diseases established functional humoral responses to vaccination, however lower than controls. Age, comorbidities and immunosuppression were associated with poor immunological responses.

Decline in Antibody Concentration 6 Months After Two Doses of SARS-CoV-2 BNT162b2 Vaccine in Solid Organ Transplant Recipients and Healthy Controls.

Background: Previous studies have indicated inferior responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccination in solid organ transplant (SOT) recipients. We examined the development of anti-receptor-binding domain (RBD) immunoglobulin G (IgG) after two doses of BNT162b2b in SOT recipients 6 months after vaccination and compared to that of immunocompetent controls. Methods: We measured anti-RBD IgG after two doses of BNT162b2 in 200 SOT recipients and 200 matched healthy controls up to 6 months after first vaccination. Anti-RBD IgG concentration and neutralizing capacity of antibodies were measured at first and second doses of BNT162b2 and 2 and 6 months after the first dose. T-cell responses were measured 6 months after the first dose. Results: In SOT recipients, geometric mean concentration (GMC) of anti-RBD IgG increased from first to second dose (1.14 AU/ml, 95% CI 1.08-1.24 to 11.97 AU/ml, 95% CI 7.73-18.77) and from second dose to 2 months (249.29 AU/ml, 95% CI 153.70-385.19). Six months after the first vaccine, anti-RBD IgG declined (55.85 AU/ml, 95% CI 36.95-83.33). At all time points, anti-RBD IgG was lower in SOT recipients than that in controls. Fewer SOT recipients than controls had a cellular response (13.1% vs. 59.4%, p < 0.001). Risk factors associated with humoral non-response included age [relative risk (RR) 1.23 per 10-year increase, 95% CI 1.11-1.35, p < 0.001], being within 1 year from transplantation (RR 1.55, 95% CI 1.30-1.85, p < 0.001), treatment with mycophenolate (RR 1.54, 95% CI 1.09-2.18, p = 0.015), treatment with corticosteroids (RR 1.45, 95% CI 1.10-1.90, p = 0.009), kidney transplantation (RR 1.70, 95% CI 1.25-2.30, p = 0.001), lung transplantation (RR 1.63, 95% CI 1.16-2.29, p = 0.005), and de novo non-skin cancer comorbidity (RR 1.52, 95% CI, 1.26-1.82, p < 0.001). Conclusion: Immune responses to BNT162b2 are inferior in SOT recipients compared to healthy controls, and studies aiming to determine the clinical impact of inferior vaccine responses are warranted.

Modeling of waning immunity after SARS-CoV-2 vaccination and influencing factors.

SARS-CoV-2 vaccines are crucial in controlling COVID-19, but knowledge of which factors determine waning immunity is limited. We examined antibody levels and T-cell gamma-interferon release after two doses of BNT162b2 vaccine or a combination of ChAdOx1-nCoV19 and BNT162b2 vaccines for up to 230 days after the first dose. Generalized mixed models with and without natural cubic splines were used to determine immunity over time. Antibody responses were influenced by natural infection, sex, and age. IgA only became significant in naturally infected. A one-year IgG projection suggested an initial two-phase response in those given the second dose delayed (ChAdOx1/BNT162b2) followed by a more rapid decrease of antibody levels. T-cell responses correlated significantly with IgG antibody responses. Our results indicate that IgG levels will drop at different rates depending on prior infection, age, sex, T-cell response, and the interval between vaccine injections. Only natural infection mounted a significant and lasting IgA response.

Prediction of Respiratory Failure and Mortality in COVID-19 Patients Using Long Pentraxin PTX3.

The course of COVID-19 is unpredictable, ranging from asymptomatic to respiratory failure and death. Prognostic biomarkers are urgently needed. We hypothesized that long pentraxin PTX3 could be a valuable plasma biomarker due to its essential role in inflammatory processes. In a prospective hospitalized COVID-19 derivation cohort (n = 126) during the spring of 2020, we measured PTX3 within 4 days of admission. The predictive value of mechanical ventilation (MV) and 30-day mortality compared with clinical parameters and other markers of inflammation were assessed by logistic regression analysis and expressed as odds ratio (OR) with 95% confidence interval (CI). Analyses were repeated in a prospective validation cohort (n = 112) of hospitalized patients with COVID-19 treated with remdesivir and dexamethasone. Thirty-day mortality in the derivation cohort was 26.2%. In patients who died, the median PTX3 concentration upon admission was 19.5 ng/mL (IQR: 12.5-33.3) versus 6.6 ng/mL (IQR 2.9-12.3) (p < 0.0001) for survivors. After adjustment for covariates, the odds of 30-day mortality increased two-fold for each doubling of PTX3 (OR 2.03 [95% CI: 1.23-3.34], p = 0.006), which was also observed in the validation cohort (OR 1.70 [95% CI: 1.09-2.67], p = 0.02). Similarly, PTX3 levels were associated with MV. After adjustment for covariates, OR of MV was 2.34 (95% CI: 1.33-4.12, p = 0.003) in the derivation cohort and 1.64 (95% CI: 1.03-2.62, p = 0.04) in the validation cohort. PTX3 appears to be a useful clinical biomarker to predict 30-day respiratory failure and mortality risk in COVID-19 patients treated with and without remdesivir and dexamethasone.

Humoral response to two doses of BNT162b2 vaccination in people with HIV.

BACKGROUND: People with HIV (PWH) are at increased risk of severe COVID-19. We aimed to determine humoral responses in PWH and controls who received two doses of BNT162b2. METHODS: In 269 PWH and 538 age-matched controls, we measured IgG and neutralizing antibodies specific for the receptor-binding domain of SARS-CoV-2 at baseline, 3 weeks and 2 months after the first dose of BNT162b2. RESULTS: IgG antibodies increased from baseline to 3 weeks and from 3 weeks to 2 months in both groups, but the concentrations of IgG antibodies were lower in PWH than that in controls at 3 weeks and 2 months (p = 0.025 and <0.001), respectively. The IgG titres in PWH with a humoral response at 2 months were 77.9% (95% confidence interval [62.5%-97.0%], age- and sex-adjusted p = 0.027) of controls. CONCLUSIONS: Reduced IgG antibody response to vaccination with BNT162b2 was found in PWH, and thus increased awareness of breakthrough infections in PWH is needed.

SARS-CoV-2 Antibodies Mediate Complement and Cellular Driven Inflammation.

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to constitute a serious public health threat worldwide. Protective antibody-mediated viral neutralization in response to SARS-CoV-2 infection has been firmly characterized. Where the effects of the antibody response are generally considered to be beneficial, an important biological question regarding potential negative outcomes of a SARS-CoV-2 antibody response has yet to be answered. We determined the distribution of IgG subclasses and complement activation levels in plasma from convalescent individuals using in-house developed ELISAs. The IgG response towards SARS-CoV-2 receptor-binding domain (RBD) after natural infection appeared to be mainly driven by IgG1 and IgG3 subclasses, which are the main ligands for C1q mediated classical complement pathway activation. The deposition of the complement components C4b, C3bc, and TCC as a consequence of SARS-CoV-2 specific antibodies were depending primarily on the SARS-CoV-2 RBD and significantly correlated with both IgG levels and disease severity, indicating that individuals with high levels of IgG and/or severe disease, might have a more prominent complement activation during viral infection. Finally, freshly isolated monocytes and a monocyte cell line (THP-1) were used to address the cellular mediated inflammatory response as a consequence of Fc-gamma receptor engagement by SARS-CoV-2 specific antibodies. Monocytic Fc gamma receptor charging resulted in a significant rise in the secretion of the pro-inflammatory cytokine TNF-α. Our results indicate that SARS-CoV-2 antibodies might drive significant inflammatory responses through the classical complement pathway and via cellular immune-complex activation that could have negative consequences during COVID-19 disease. We found that increased classical complement activation was highly associated to COVID-19 disease severity. The combination of antibody-mediated complement activation and subsequent cellular priming could constitute a significant risk of exacerbating COVID-19 severity.

SARS-CoV-2 Neutralizing Antibody Responses towards Full-Length Spike Protein and the Receptor-Binding Domain.

Tools to monitor SARS-CoV-2 transmission and immune responses are needed. We present a neutralization ELISA to determine the levels of Ab-mediated virus neutralization and a preclinical model of focused immunization strategy. The ELISA is strongly correlated with the elaborate plaque reduction neutralization test (ρ = 0.9231, p < 0.0001). The neutralization potency of convalescent sera strongly correlates to IgG titers against SARS-CoV-2 receptor-binding domain (RBD) and spike (ρ = 0.8291 and 0.8297, respectively; p < 0.0001) and to a lesser extent with the IgG titers against protein N (ρ = 0.6471, p < 0.0001). The preclinical vaccine NMRI mice models using RBD and full-length spike Ag as immunogens show a profound Ab neutralization capacity (IC50 = 1.9 × 104 to 2.6 × 104 and 3.9 × 103 to 5.2 × 103, respectively). Using a panel of novel high-affinity murine mAbs, we also show that a majority of the RBD-raised mAbs have inhibitory properties, whereas only a few of the spike-raised mAbs do. The ELISA-based viral neutralization test offers a time- and cost-effective alternative to the plaque reduction neutralization test. The immunization results indicate that vaccine strategies focused only on the RBD region may have advantages compared with the full spike.

SARS-CoV-2 Antibody Responses Are Correlated to Disease Severity in COVID-19 Convalescent Individuals.

Globally, the COVID-19 pandemic has had extreme consequences for the healthcare system and has led to calls for diagnostic tools to monitor and understand the transmission, pathogenesis, and epidemiology, as well as to evaluate future vaccination strategies. In this study, we have developed novel, to our knowledge, flexible ELISA-based assays for specific detection of human SARS-CoV-2 Abs against the receptor-binding domain, including an Ag sandwich ELISA relevant for large population screening and three isotype-specific assays for in-depth diagnostics. Their performance was evaluated in a cohort of 350 convalescent participants with previous COVID-19 infection, ranging from asymptomatic to critical cases. We mapped the Ab responses to different areas on protein N and S and showed that the IgM, A, and G Ab responses against receptor-binding domain are significantly correlated to the disease severity. These assays and the data generated from them are highly relevant for diagnostics and prognostics and contribute to the understanding of long-term COVID-19 immunity.