Fig. 6

Bacterial SyBV overexpressing spike protein S1 stimulate virus-specific immunity through antibody production and T-cell activation. a Schematic representation of the structure of the chimeric Lpp-OmpA construct with SARS-CoV-2 spike protein S1 in the bacterial outer membrane. b TEM images of engineered SyBV overexpressing S1 (SyBV^S1). Scale bars, 200 nm. c Western blot analysis of IPTG-induced bacterial lysates and SyBV^S1 with anti-His Tag antibody. The filled triangle indicates the Lpp-OmpA-S1 complex. d S1-specific IgG titers after the last immunization with OMV^S1 or SyBV^S1 (n = 5). e The level of S1-specific CD4⁺ T-cell-derived IFN-γ after CD4⁺ T-cells were isolated from immunized spleens (three independent samples). All data are presented as the mean ± s.e.m. ^***P < 0.001; ns, not significant by two-way ANOVA with Tukey’s post-test versus the sham group