Studies on aspects of the immune response in viral infections including: cross-protection between Chikungunya and Mayaro viruses; analysis of Zika virus E protein antigenic epitopes; and evaluation of response to inactivated SARS-CoV-2 vaccine

Author(s)

Marcilio Jorge Fumagalli

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2022-01-05

Examining board members

Luiz Tadeu Moraes Figueiredo; Ademilson Panunto Castelo; Benedito Antonio Lopes da Fonseca; José Luiz Proença Modena

• Advisor: Luiz Tadeu Moraes Figueiredo; Victor Hugo Aquino Quintana

Abstract

This Doctoral Thesis analyzes different aspects of immune responses to viral infections and includes 3 studies. In Part I, we have a study on the cross-protection between Chikungunya and Mayaro viruses where it was possible to conclude that: The immune response to CHIKV provides partial cross-protection against secondary MAYV infection, reducing tissue viral load and histopathological damage. Anti-CHIKV antibodies from humans and mice have low cross-neutralization against MAYV infection. After secondary MAYV infection in mice, high titers of antibodies with cross-neutralizing activity were observed. Depletion of immune system cells indicated that a combination of adaptive immune cells might be relevant in cross-protection against MAYV. The reduction of pro-inflammatory cytokines, NK cells, and inflammatory monocytes during MAYV secondary infection, suggests a role for innate immunity in cross-protection. In Part II, we have an analysis of antigenic epitopes of Zika virus E protein, where it was possible to: Select 9 linear ZIKV protein E peptides based on the cross-reactivity of anti-DENV IgG antibodies. Of the 9 peptides selected, 3 belong to the domain I (DI) of protein E, 2 to DII, supposedly being genus or group-specific, and 4 peptides to DIII, probably corresponding to immunodominant antigenic regions of flaviviruses. Serum cross-neutralization of sera from convalescent DENV patients against ZIKV infection unrelated to the 9 linear peptides mentioned was observed. Most of the DENV convalescent sera exhibited ADE, potentiating a ZIKV infection and, when depleting those with affinity for the 9 linear peptides selected, they reduced their activity, suggesting that antibodies against such peptides may be involved in ADE for ZIKV. In Part III, we have an evaluation of the immune response to the inactivated SARS-CoV-2 vaccine, where we conclude that: Individuals vaccinated twice with the inactivated SARS-CoV-2 seroconvert, producing high levels of IgG anti-Spike (S) viral protein with significant neutralizing capacity, which is significantly reduced against SARS-CoV-2 and the Gamma and Zeta variants after 6 months. Antibodies from animals vaccinated by the inactivated virus vaccine were less neutralizing against the Gamma and Zeta variants of SARS-CoV-2, but with a significant increase 3 days after infection. The stimulation of mouse splenic cells from immunized mice with SARS-CoV-2 inactivated antigens induced lymphoproliferation even to the antigens of the different viral variants. Prior immunization with inactivated SARS-CoV-2 reduced the burden of Gamma and Zeta variants in mouse lungs by almost 100 times. Undetectable levels of IL-6 and TNF-α in mice immunized after infection with WT strains and the Zeta variant were associated with a reduction in the pulmonary inflammatory infiltrate, evidencing a protective role of previous immunization by inactivated SARS-CoV-2. (AU)

• FAPESP's process: 18/09383-3 - Study about Flavivirus epitopes with medical importance in Brazil and its antibodies
• Grantee: Marcilio Jorge Fumagalli
• Support Opportunities: Scholarships in Brazil - Doctorate