The novel coronavirus 2019 (COVID-19) pandemic, caused by the novel coronavirus, severe acute respiratory syndrome 2 (SARS-CoV-2), has had a major impact on the health care system and the global economy. SARS-CoV-2 causes severe, asymptomatic infection, sometimes fatal. Scientists note that active replication of the virus occurs in the early stage of infection, while the host immune system functions critically in the later stage of infection. This is why researchers have devised a strategy to use antiviral agents to target SARS-CoV-2 in its early stage of infection.
Study: Relationship between SARS-CoV-2 antibody titer and COVID-19 severity. Image Credit: peterschreiber.media/ / Shutterstock
Several studies have evaluated the host’s immune response along with the progression of COVID-19 disease. These studies demonstrated that although the immune system plays a vital role in protecting the individual from disease, overcoming immune responses, such as a cytokine storm, negatively affects the host.
Scientists report that the role of antibody-based immune responses in COVID-19 is poorly understood. Previous studies have linked individuals with severe COVID-19 to high levels of SARS-CoV-2 antibodies. However, it is not well understood whether high titers of SARS-CoV-2 antibodies exacerbate the clinical outcome of the disease, or if severe disease leads to the production of a high concentration of antibodies.
To address the aforementioned research gap, scientists have focused on determining the cause-and-effect relationship between SARS-CoV-2 antibody titer and COVID-19 disease severity. The study was published in Journal of Microbiology, Immunology and Infection.
In this study, researchers recruited hospitalized COVID-19 patients between February 2020 and August 2020. They measured neutralizing antibodies (NAb) and receptor-binding domain (RBD) antibodies from blood samples obtained from participants. The scientists also estimated the results of chest radiographs (CXR) to determine the severity of the disease.
The study reported high antibody titers in elderly patients with COVID-19. These patients have pneumonia and need oxygen support. The scientists compared the peak time for COVID-19 antibody levels and CXR scores and observed that CXR scores were significantly maximized earlier than in NAb and RBD antibody titers. Because there is a direct relationship between highest CXR score and highest level of specific antibody to SARS-CoV-2, the authors concluded that production of high antibody titers resulted in severe clinical outcomes.
Usually, when a pathogen invades the human body (for example, a virus), the innate and adaptive immune system protects against the virus. Several studies have indicated that the cellular immune system is involved in removing pathogens from the body, while humoral immunity primarily protects against new infections.
As previous studies have linked elevated production of SARS-CoV-2 antibodies to manifestations of severe disease or mortality, this has led to the perception that massive production of SARS-CoV-2 antibodies enhances disease progression by antibody-dependent enhancement (ADE). ). ). Similar observations have been recorded for the dengue virus. Interestingly, studies evaluating the efficacy of plasma therapy in the convalescent period of COVID-19 patients did not reveal any negative effects when patients were treated with a high proportion of SARS-CoV-2 antibodies. Furthermore, the animals vaccinated with the COVID-19 vaccine showed no signs of ADE. These results prove that ADE is not the likely cause of COVID-19 disease development.
Scientists believe that uncontrolled replication of the virus and cases of excessive inflammation could be the reason for the production of high levels of SARS-CoV-2 antibodies in severely infected COVID-19 patients. In this study, scientists speculated that high levels of NAb and RBD antibodies were elicited by the high viral load, erratic immune responses, and uncontrolled viral replication in severely infected patients.
The study reported that elderly patients showed a higher level of SARS-CoV-2 antibodies compared to younger patients. This result indicates that elderly patients are more likely to develop severe infections due to the production of high titers of SARS-CoV-2 antibodies. Although the researchers studied changes in pro-inflammatory cytokines, results were obtained for only fifteen patients. This is why they failed to make a strong conclusion regarding the association between proinflammatory cytokines, T-cell and B-cell immunity, and COVID-19 disease severity. Future research should take advantage of a larger sample size to determine whether or not these relationships exist.
The authors highlight some limitations of the study, which includes the relatively small study cohort containing participants from one hospital. They did not measure the neutralizing ability of the SARS-CoV-2 antibody, and as a result, they failed to confirm whether a higher concentration of Nab had a more significant effect on neutralizing SARS-CoV-2 virus. In this study, high titers of SARS-CoV-2 antibody were closely associated with severe COVID-19 manifestations. Understanding the mechanisms behind such an association will be a critical step toward developing new vaccines and therapies to prevent, treat, and treat SARS-CoV-2 infection.