AUTHOR=Yu Xiaoli , Wang Li , Yang Xinru , Zhang Songsong , Li Guiwei , Zhang Lanlan , Li Jiaxuan , Wang Xiaona , Zhou Han , Jiang Yanping , Cui Wen , Li Yijing , Tang Lijie , Qiao Xinyuan 

TITLE=Lactobacillus casei Ghosts as a Vehicle for the Delivery of DNA Vaccines Mediate Immune Responses

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.849409

DOI=10.3389/fimmu.2022.849409

ISSN=1664-3224

ABSTRACT=<p>We developed <italic>Lactobacillus casei</italic> bacterial ghosts (BGs) as vehicles for delivering DNA vaccines and analyzed their effects on immune responses. Uptake of the plasmids encoding the enhanced green fluorescent protein (pCI-EGFP) and BGs loaded with pCI-EGFP by macrophages was investigated using fluorescence microscopy and flow cytometry. The results showed that pCI-EGFP-loaded <italic>L. casei</italic> BGs were efficiently taken up by macrophages. <italic>Lactobacillus casei</italic> BGs loaded with plasmids encoding VP6 protein of PoRV (pCI-PoRV-VP6) significantly upregulated the mRNA expression of <uri xlink:href="http://dict.youdao.com/w/interleukin/" xmlns:xlink="http://www.w3.org/1999/xlink">interleukin</uri> (IL)-1β, IL-10, <uri xlink:href="http://dict.youdao.com/w/tumor%20necrosis%20factor/" xmlns:xlink="http://www.w3.org/1999/xlink">tumor necrosis factor</uri> (TNF)-α, inducible nitric oxide synthase (iNOS), arginase-1 (Arg-1), Mannose receptor (CD206) toll-like receptor (TLR)-2, TLR4, and TLR9 in macrophages. The levels of markers of M1 polarization (IL-10 and TNF-α) and M2 polarization (Arg-1 and CD206) were increased in macrophages incubated with pCI-PoRV-VP6-loaded BGs compared with the control group. The results of the enzyme-linked immunosorbent assay showed that the secretion of IL-1β, IL-10, and TNF-α in macrophages was significantly upregulated compared with the control group. Flow cytometry demonstrated that <italic>L. casei</italic> BGs loaded with pCI-PoRV-VP6 promoted the maturation of dendritic cells (DCs). Following incubation with pCI-PoRV-VP6-loaded BGs, the mRNA expression levels of IL-1β, IL-6 and interferon (IFN)-γ in DCs were significantly increased. ELISA assay showed the secretion of the IL-1β, IL-6, IFN-γ IL-10 and TNF-α in DCs were upregulated significantly. Thus, <italic>L. casei</italic> BGs promoted the maturation and activation of DCs. We analyzed the stimulatory capacity of DCs in a mixed lymphocyte reaction with allogeneic T cells. T cell proliferation increased upon incubation with DCs stimulated by BGs. After immunizing mice with BGs loaded with pCI-PoRV-VP6, the specific IgG levels in the serum were higher than those elicited by BGs loaded with pCI-PoRV-VP6. BGs loaded with pCI-PoRV-VP6 on Th1 and Th2 cytokines polarized T cells into the Th1 type and increased the proportion of CD4<sup>+</sup>/CD8<sup>+</sup> T cells. These results indicate <italic>L. casei</italic> BGs effectively mediate immune responses and can be used as delivery system for DNA vaccination.</p>