SARS-CoV-2 seroprevalence in asymptomatic or mild symptomatic people and symptomatic patients with negative PCR results: The hidden perspective in epidemiological reports

BackgroundSARS-CoV-2 has led to the current pandemic of respiratory disease. The reports of confirmed COVID-19 cases based on molecular tests do not completely cover the total number of infected people. These reports do not include the asymptomatic or mildly symptomatic patients and also the patients with false-negative RT-PCR results, while the infection is contagious in all of these conditions. ObjectiveIn this study, we tried to improve our conception of the hidden perspective of SARS-CoV-2 in epidemiological reports. MethodsFrom May 30 to June 17, 2020, blood samples were collected from two groups of people: asymptomatic or mild symptomatic volunteer participants and severe symptomatic hospitalized patients with negative PCR results. Detection of SARS-CoV-2 antibody was done with ELISA kit targeting N or S proteins. ResultsTotally 716 samples from volunteer participants and 81 samples from symptomatic hospitalized patients with negative PCR were evaluated. The test performance-adjusted seroprevalence (95% CI) of SARS-CoV-2 anti-N IgG was 17.3% (8.8%, 25.8%) for volunteers and 25.5% (12.8%, 39.7%) for anti-N and S IgM in hospitalized group. There was an association between high-risk occupations, high-risk behaviors, or symptomatic diseases with positive SARA-Cov-2 N antibody results. Among anti-N positive infected individuals, 49.2% (21.4%, 78.8%) were anti-S positive. ConclusionThe results showed that SARS-COV-2 infection occurs in asymptomatic or mildly symptomatic individuals, but in more than half of them, the produced antibody is not protective. Findings of hospitalized patients also showed that the combination of IgM assay with real-time PCR improves the detection of the disease by more than 25% in negative molecular cases.

Full length antigen priming enhances the CTL epitope-based DNA vaccine efficacy.

Although CD8+ cytotoxic T lymphocyte (CTL) epitope-based DNA vaccination is valuable experience on vaccine research but many attempts are still continued to achieve acceptable protective response. To study the role of full length antigen in CTL epitope immunization, we evaluated cellular immunity of diverse patterns of complete Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) and the immunodominant CTL epitope (498-505) DNA injection in C57BL/6 mice. Optimal immune response was observed in the group immunized with the full length of gB in the first injection and CTL epitope in the second and third vaccination as assessed by lymphocyte proliferation assay (MTT), cytokine assay (ELISA) and CTL assay. B cell and spatially CD4+ T cell epitopes in full length protein might be important for appropriate priming of CTL immune response. These findings may have important implication for the improvement of CTL epitope based DNA vaccine against HSV and other pathogens.

Evaluation of apoptotic and anti-apoptotic genes on efficacy of DNA vaccine encoding glycoprotein B of Herpes Simplex Virus type 1.

Many approaches have so far been tried to enhance the immunogenicity of DNA vaccine. These include the use of various factors that induce apoptosis or anti-apoptosis effects when co-delivered with DNA vaccine. In the present study, the effects of pro-apoptotic Bax encoding plasmid (pBax) and anti-apoptotic Bcl-X(L) encoding plasmid (pBcl-xl), intradermally co-injected with glycoprotein B (gB) of Herpes Simplex Virus (HSV)-1 encoding plasmid (pgB) into the C57BL/6 mice were evaluated. Immune responses of the mice to the antigen were assessed by antibody assay, lymphoproliferative responses as well as cytokine and cytotoxic T-lymphocyte (CTL) assay. Analysis of the humoral and cellular responses showed that the mice immunized with pBax and pgB induced higher levels of antibody and Interleukin-4 as well as stronger lymphocyte proliferative responses and cytotoxic activity compared to those mice received pgB alone. pBcl-xl when intradermally co-injected with pgB showed no significant enhancement in immune responses comparing to pgB.