Relationship between SARS-CoV-2 antibody titer and the severity of COVID-19

Primary SARS-CoV-2 variant of concern infections elicit broad antibody Fc-mediated effector functions and memory B cell responses

Neutralization of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by human sera is a strong correlate of protection against symptomatic and severe Coronavirus Disease 2019 (COVID-19). The emergence of antigenically distinct SARS-CoV-2 variants of concern (VOCs) and the relatively rapid waning of serum antibody titers, however, raises questions about the sustainability of serum protection. In addition to serum neutralization, other antibody functionalities and the memory B cell (MBC) response are suggested to help maintaining this protection. In this study, we investigate the breadth of spike (S) protein-specific serum antibodies that mediate effector functions by interacting with Fc-gamma receptor IIa (FcγRIIa) and FcγRIIIa, and of the receptor binding domain (RBD)-specific MBCs, following a primary SARS-CoV-2 infection with the D614G, Alpha, Beta, Gamma, Delta, Omicron BA.1 or BA.2 variant. Irrespectively of the variant causing the infection, the breadth of S protein-specific serum antibodies that interact with FcγRIIa and FcγRIIIa and the RBD-specific MBC responses exceeded the breadth of serum neutralization, although the Alpha-induced B cell response seemed more strain-specific. Between VOC groups, both quantitative and qualitative differences in the immune responses were observed, suggesting differences in immunogenicity. Overall, this study contributes to the understanding of protective humoral and B cell responses in the light of emerging antigenically distinct VOCs, and highlights the need to study the immune system beyond serum neutralization to gain a better understanding of the protection against emerging variants.

Regulatory T and CXCR3+ Circulating Tfh Cells Concordantly Shape the Neutralizing Antibody Responses in Individuals Who Have Recovered from Mild COVID-19

Regulatory T (Treg) cells are involved in the antiviral immune response in patients with coronavirus disease 2019 (COVID-19); however, whether Treg cells are involved in the neutralizing antibody (nAb) response remains unclear. Here, we found that individuals who recovered from mild but not severe COVID-19 had significantly greater frequencies of Treg cells and lower frequencies of CXCR3+ circulating T follicular helper (cTfh) cells than healthy controls. Furthermore, the frequencies of Treg and CXCR3+ cTfh cells were negatively and positively correlated with the nAb responses, respectively, and Treg cells was inversely associated with CXCR3+ cTfh cells in individuals who recovered from mild COVID-19 but not in those with severe disease. Mechanistically, Treg cells inhibited memory B-cell differentiation and antibody production by limiting the activation and proliferation of cTfh cells, especially CXCR3+ cTfh cells, and functional molecule expression. This study provides novel insight showing that mild COVID-19 elicits concerted nAb responses, which are shaped by both Treg and Tfh cells.

Tracking the evolution of anti-SARS-CoV-2 antibodies and long-term humoral immunity within 2 years after COVID-19 infection

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that gave rise to COVID-19 infection produced a worldwide health crisis. The virus can cause a serious or even fatal disease. Comprehending the complex immunological responses triggered by SARS-CoV-2 infection is essential for identifying pivotal elements that shape the course of the disease and its enduring effects on immunity. The span and potency of antibody responses provide valuable perspicuity into the resilience of post-infection immunity. The analysis of existing literature reveals a diverse controversy, confining varying data about the persistence of particular antibodies as well as the multifaceted factors that impact their development and titer, Within this study we aimed to understand the dynamics of anti-SARS-CoV-2 antibodies against nucleocapsid (anti-SARS-CoV-2 (N)) and spike (anti-SARS-CoV-2 (N)) proteins in long-term immunity in convalescent patients, as well as the factors influencing the production and kinetics of those antibodies. We collected 6115 serum samples from 1611 convalescent patients at different post-infection intervals up to 21 months Study showed that in the fourth month, the anti-SARS-CoV-2 (N) exhibited their peak mean value, demonstrating a 79% increase compared to the initial month. Over the subsequent eight months, the peak value experienced a modest decline, maintaining a relatively elevated level by the end of study. Conversely, anti-SARS-CoV-2 (S) exhibited a consistent increase at each three-month interval over the 15-month period, culminating in a statistically significant peak mean value at the study's conclusion. Our findings demonstrate evidence of sustained seropositivity rates for both anti-SARS-CoV-2 (N) and (S), as well as distinct dynamics in the long-term antibody responses, with anti-SARS-CoV-2 (N) levels displaying remarkable persistence and anti-SARS-CoV-2 (S) antibodies exhibiting a progressive incline.

Clinical and serological predictors of post COVID-19 condition-findings from a Canadian prospective cohort study

Introduction

More than 3 years into the pandemic, there is persisting uncertainty as to the etiology, biomarkers, and risk factors of Post COVID-19 Condition (PCC). Serological research data remain a largely untapped resource. Few studies have investigated the potential relationships between post-acute serology and PCC, while accounting for clinical covariates.

Methods

We compared clinical and serological predictors among COVID-19 survivors with (n = 102 cases) and without (n = 122 controls) persistent symptoms ≥12 weeks post-infection. We selected four primary serological predictors (anti-nucleocapsid (N), anti-Spike, and anti-receptor binding domain (RBD) IgG titres, and neutralization efficiency), and specified clinical covariates a priori.

Results

Similar proportions of PCC-cases (66.7%, n = 68) and infected-controls (71.3%, n = 87) tested positive for anti-N IgG. More cases tested positive for anti-Spike (94.1%, n = 96) and anti-RBD (95.1%, n = 97) IgG, as compared with controls (anti-Spike: 89.3%, n = 109; anti-RBD: 84.4%, n = 103). Similar trends were observed among unvaccinated participants. Effects of IgG titres on PCC status were non-significant in univariate and multivariate analyses. Adjusting for age and sex, PCC-cases were more likely to be efficient neutralizers (OR 2.2, 95% CI 1.11-4.49), and odds was further increased among cases to report deterioration in quality of life (OR 3.4, 95% CI 1.64-7.31). Clinical covariates found to be significantly related to PCC included obesity (OR 2.3, p = 0.02), number of months post COVID-19 (OR 1.1, p < 0.01), allergies (OR 1.8, p = 0.04), and need for medical support (OR 4.1, p < 0.01).

Conclusion

Despite past COVID-19 infection, approximately one third of PCC-cases and infected-controls were seronegative for anti-N IgG. Findings suggest higher neutralization efficiency among cases as compared with controls, and that this relationship is stronger among cases with more severe PCC. Cases also required more medical support for COVID-19 symptoms, and described complex, ongoing health sequelae. More data from larger cohorts are needed to substantiate results, permit subgroup analyses of IgG titres, and explore for differences between clusters of PCC symptoms. Future assessment of IgG subtypes may also elucidate new findings.

High interleukin-6 levels induced by COVID-19 pneumonia correlate with increased circulating follicular helper T cell frequency and strong neutralization antibody response in the acute phase of Omicron breakthrough infection

Background

Acute immune responses to coronavirus disease 2019 (COVID-19) are influenced by variants, vaccination, and clinical severity. Thus, the outcome of these responses may differ between vaccinated and unvaccinated patients and those with and without COVID-19-related pneumonia. In this study, these differences during infection with the Omicron variant were investigated.

Methods

A total of 67 patients (including 47 vaccinated and 20 unvaccinated patients) who were hospitalized within 5 days after COVID-19 symptom onset were enrolled in this prospective observational study. Serum neutralizing activity was evaluated using a pseudotyped virus assay and serum cytokines and chemokines were measured. Circulating follicular helper T cell (cTfh) frequencies were evaluated using flow cytometry.

Results

Twenty-five patients developed COVID-19 pneumonia on hospitalization. Although the neutralizing activities against wild-type and Delta variants were higher in the vaccinated group, those against the Omicron variant as well as the frequency of developing pneumonia were comparable between the vaccinated and unvaccinated groups. IL-6 and CXCL10 levels were higher in patients with pneumonia than in those without it, regardless of their vaccination status. Neutralizing activity against the Omicron variant were higher in vaccinated patients with pneumonia than in those without it. Moreover, a distinctive correlation between neutralizing activity against Omicron, IL-6 levels, and cTfh proportions was observed only in vaccinated patients.

Conclusions

The present study demonstrates the existence of a characteristic relationship between neutralizing activity against Omicron, IL-6 levels, and cTfh proportions in Omicron breakthrough infection.

Evaluation of antibody titers in COVID-19 patients with cerebral or pulmonary symptoms and mild symptoms

Background and Objectives

This study aimed to compare the production of antibodies in three different groups of patients with COVID-19. These groups included patients with pulmonary and cerebral symptoms, as well as those with mild symptoms.

Materials and Methods

Blood samples were collected from 80 patients admitted to COVID-19-specific hospitals. The patients had various forms of SARS-CoV-2 disease, including those with pulmonary symptoms, brain involvement, and those with positive PCR test results but mild symptoms. The enzyme-linked immunosorbent assay (ELISA) technique was used to determine the levels of IgM and IgG antibody titers.

Results

The levels of IgM and IgG antibody production differed significantly between groups of patients experiencing pulmonary symptoms and cerebral symptoms, with mild symptom patients also showing differences (P=0.0068), (P=0.0487), (P<0.0001), and (P=0.0120), respectively. Furthermore, there was no significant relationship between IgM antibody secretion and age or pulmonary involvement (P=0.1959). However, there was a direct and significant relationship between age and brain involvement (P=0.0317).

Conclusion

The findings of this study revealed that the risk of central nervous system involvement increases with age and that older people have lower antibody levels than younger people. Consequently, strengthening the immune systems of people over the age of 78 during this pandemic through vaccination and nutrition is very effective in reducing mortality in this age group.

A Correlation Study to Comprehend the SAR-CoV-2 Viral Load, Antiviral Antibody Titer, and Severity of COVID-19 Symptoms Post-infection Amongst the Vaccinated Population in Kamrup District of As sam, Northeast India

BACKGROUND

As per the recommendation of the United States Food and Drug Administration, more research is needed to determine the antibody titer against COVID-19 vaccination.

OBJECTIVE

The study aimed to understand the relationship between the antibody titer to the demographics, infection severity, and cycle threshold (CT) values of confirmed COVID-19 patients.

METHODS

Initially, we obtained consent from 185 populations and included sixty RT-PCRpositive COVID-19 patients from Kamrup District in the Northeast State of Assam, India. The vaccination status was recorded and tested for the level of serum immunoglobulin (IgG). The CT values, gender, and clinical symptoms-based scoring (CSBS) correlated with their IgG value.

RESULTS

Around 48% of participants gained an antibody titer more than the threshold value and showed CT values between 18-25. Moreover, the maximum distributed score above the average was found between the CT values 18-25.

CONCLUSION

The IgG titer value differs significantly amongst the vaccinated population, which may depend upon their genetic and demographic variability.

Longitudinal Analysis of Antibody Response Following SARS-CoV-2 Infection Depending on Disease Severity: A Prospective Cohort Study

OBJECTIVE

Severe coronavirus disease 19 (COVID-19) is characterized by a dysregulated inflammatory response, with humoral immunity playing a central role in the disease course. The objective of this study was to assess the immune response and the effects of vaccination in recovered individuals with variable disease severity up to one year following natural infection.

METHODS

A prospective cohort study was conducted including patients with laboratory-confirmed COVID-19. Disease severity was classified as mild, moderate, and severe based on clinical presentation and outcomes. Anti-RBD (receptor binding domain) and neutralizing antibodies were evaluated at multiple timepoints during the first year after COVID-19 diagnosis.

RESULTS

A total of 106 patients were included; of them, 28 were diagnosed with mild, 38 with moderate, and 40 with severe disease. At least one vaccine dose was administered in 58 individuals during the follow-up. Participants with mild disease presented significantly lower anti-RBD and neutralizing antibodies compared to those with moderate and severe disease up to the 3rd and 6th months after the infection, respectively. After adjusting for covariates, in the third month, severe COVID-19 was associated with significantly higher anti-RBD (β: 563.09; 95% confidence intervals (CI): 257.02 to 869.17) and neutralizing (β: 21.47; 95% CI: 12.04 to 30.90) antibodies. Among vaccinated individuals, at the 12th month, a history of moderate disease was associated with significantly higher anti-RBD levels (β: 5615.19; 95% CI: 657.92 to 10,572.46).

CONCLUSIONS

Severe COVID-19 is associated with higher anti-RBD and neutralizing antibodies up to 6 months after the infection. Vaccination of recovered patients is associated with a remarkable augmentation of antibody titers up to one year after COVID-19 diagnosis, regardless of disease severity.

Predictive values of immune indicators on respiratory failure in the early phase of COVID-19 due to Delta and precedent variants

Background

Immune response indicators in the early phase of COVID-19, including interferon and neutralizing responses against SARS-CoV-2, which predict hypoxemia remains unclear.

Methods

This prospective observational study recruited patients hospitalized with COVID-19 (before emergence of omicron variant). As the immune indicators, we assessed the serum levels of IFN-I/III, IL-6, CXCL10 and VEGF, using an ELISA at within 5 days after the onset of symptoms, and serum neutralizing responses using a pseudovirus assay. We also assessed SARS-CoV-2 viral load by qPCR using nasal-swab specimens and serum, to assess the association of indicators and viral distribution.

Results

The study enrolled 117 patients with COVID-19, of which 28 patients developed hypoxemia. None received vaccine before admission. Serum IFN-I levels (IFN-α and IFN-β), IL-6, CXCL10, LDH and CRP were significantly higher in patients who developed hypoxemia. A significant association with nasopharyngeal viral load was observed only for IFN-I. The serum levels of IFN-α, IL-6, CXCL10 were significantly associated with the presence of RNAemia. Multivariable analysis showed higher odds ratio of IFN-α, with cut-off value of 107 pg/ml, in regard to hypoxemia (Odds ratio [OR]=17.5; 95% confidence interval [CI], 4.7-85; p<0.001), compared to those of IL-6, >17.9 pg/ml (OR=10.5; 95% CI, 2.9-46; p<0.001).

Conclusions

This study demonstrated that serum IFN-α levels in the early phase of SARS-CoV-2 infection strongly predict hypoxemic respiratory failure in a manner different from that of the other indicators including IL-6 or humoral immune response, and instead sensitively reflect innate immune response against SARS-CoV-2 invasion.

An update on lateral flow immunoassay for the rapid detection of SARS-CoV-2 antibodies

Over the last three years, after the outbreak of the COVID-19 pandemic, an unprecedented number of novel diagnostic tests have been developed. Assays to evaluate the immune response to SARS-CoV-2 have been widely considered as part of the control strategy. The lateral flow immunoassay (LFIA), to detect both IgM and IgG against SARS-CoV-2, has been widely studied as a point-of-care (POC) test. Compared to laboratory tests, LFIAs are faster, cheaper and user-friendly, thus available also in areas with low economic resources. Soon after the onset of the pandemic, numerous kits for rapid antibody detection were put on the market with an emergency use authorization. However, since then, scientists have tried to better define the accuracy of these tests and their usefulness in different contexts. In fact, while during the first phase of the pandemic LFIAs for antibody detection were auxiliary to molecular tests for the diagnosis of COVID-19, successively these tests became a tool of seroprevalence surveillance to address infection control policies. When in 2021 a massive vaccination campaign was implemented worldwide, the interest in LFIA reemerged due to the need to establish the extent and the longevity of immunization in the vaccinated population and to establish priorities to guide health policies in low-income countries with limited access to vaccines. Here, we summarize the accuracy, the advantages and limits of LFIAs as POC tests for antibody detection, highlighting the efforts that have been made to improve this technology over the last few years.

Multisystem inflammatory syndrome in children: A dysregulated autoimmune disorder following COVID-19

Multisystem inflammatory syndrome in children (MIS-C) is a dysregulated autoimmune-mediated illness in genetically susceptible patients following COVID-19 with an interval of 2-6 weeks. The median age of patients with MIS-C is 6-11 years. Most common manifestations are involvement of gastrointestinal tract, cardiovascular system, hematological system, and mucocutaneous system. Respiratory tract, neurological system, musculoskeletal system, and kidney are less frequently affected. Mucocutaneous manifestations and coronary artery abnormalities characteristic for Kawasaki disease (KD) may be observed in a significant proportion of MIS-C patients that may make the differential diagnosis be difficult for some patients, especially in the post-pandemic era. The mortality rate is 1-3%. Management and prognosis of MIS-C are similar to that of KD. MIS-C and KD may share a common pathogenic process. Based on the observation of MIS-C-like illness in uninfected neonates, i.e. multisystem inflammatory syndrome in neonates, both MIS-C and KD may be a consequence of dysregulated, over-exaggerated humoral immune responses triggered by a specific infectious agent.

COVID-19 vaccination boosts the potency and breadth of the immune response against SARS-CoV-2 among recovered patients in Wuhan

The immunity of patients who recover from coronavirus disease 2019 (COVID-19) could be long lasting but persist at a lower level. Thus, recovered patients still need to be vaccinated to prevent reinfection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or its mutated variants. Here, we report that the inactivated COVID-19 vaccine can stimulate immunity in recovered patients to maintain high levels of anti-receptor-binding domain (RBD) and anti-nucleocapsid protein (NP) antibody titers within 9 months, and high neutralizing activity against the prototype, Delta, and Omicron strains was observed. Nevertheless, the antibody response decreased over time, and the Omicron variant exhibited more pronounced resistance to neutralization than the prototype and Delta strains. Moreover, the intensity of the SARS-CoV-2-specific CD4+ T cell response was also increased in recovered patients who received COVID-19 vaccines. Overall, the repeated antigen exposure provided by inactivated COVID-19 vaccination greatly boosted both the potency and breadth of the humoral and cellular immune responses against SARS-CoV-2, effectively protecting recovered individuals from reinfection by circulating SARS-CoV-2 and its variants.

Immunity after COVID-19 Recovery and Vaccination: Similarities and Differences

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is associated with a robust immune response. The development of systemic inflammation leads to a hyperinflammatory state due to cytokine release syndrome during severe COVID-19. The emergence of many new SARS-CoV-2 variants across the world deteriorates the protective antiviral immunity induced after infection or vaccination. The innate immune response to SARS-CoV-2 is crucial for determining the fate of COVID-19 symptomatology. T cell-mediated immunity is the main factor of the antiviral immune response; moreover, SARS-CoV-2 infection initiates a rapid B-cell response. In this paper, we present the current state of knowledge on immunity after COVID-19 infection and vaccination. We discuss the mechanisms of immune response to various types of vaccines (nucleoside-modified, adenovirus-vectored, inactivated virus vaccines and recombinant protein adjuvanted formulations). This includes specific aspects of vaccination in selected patient populations with altered immune activity (the elderly, children, pregnant women, solid organ transplant recipients, patients with systemic rheumatic diseases or malignancies). We also present diagnostic and research tools available to study the anti-SARS-CoV-2 cellular and humoral immune responses.