Abstract
Probiotics are essential for the prevention of virus invasion and the maintenance of the immune balance. However, the mechanism of competition between probiotics and virus are unknown. The objectives of this study were to isolate the surface layer (S-layer) protein from L. acidophilus ATCC 4356 as a new antiviral material, to evaluate the stimulatory effects of the S-layer protein on mouse dendritic cells (DCs) and to verify its ability to inhibit the invasion of H9N2 avian influenza virus (AIV) in DCs. We found that the S-layer protein induced DCs activation and up-regulated the IL-10 secretion. The invasion and replication of the H9N2 virus in mouse DCs was successfully demonstrated. However, the invasion of H9N2 virus into DCs could be inhibited by treatment with the S-layer protein prior to infection, which was verified by the reduced hemagglutinin (HA) and neuraminidase (NA) mRNA expression, and nucleoprotein (NP) protein expression in the DCs. Furthermore, treatment with the S-layer protein increases the Mx1, Isg15, and Ddx58 mRNA expressions, and remits the inflammatory process to inhibit H9N2 AIV infection. In conclusion, the S-layer protein stimulates the activation of mouse DCs, inhibits H9N2 virus invasion of DCs, and stimulates the IFN-I signaling pathway. Thus, the S-layer protein from Lactobacillus is a promising biological antiviral material for AIV prevention.
Highlights
The mucosa contains a diverse microbial community called the microbiota, which included numerous viruses
The surface layer (S-layer) protein was extracted from L. acidophilus ATCC 4356 with guanidine hydrochloride (GuHCl) (Figure 1A)
To determine the cytotoxic effect of the S-layer protein extracted from L. acidophilus ATCC 4356, we used the Cell Counting Kit-8 (CCK-8) assay to detect cell viability after treatment with different concentrations of the S-layer protein (Figure 1B)
Summary
The mucosa contains a diverse microbial community called the microbiota, which included numerous viruses. Dendritic cells (DCs) underneath the epithelial mucosa are important antigen presenting cells (APC) that play an important role in the immune response and the maintenance of the mucosal barrier (Foligne et al, 2007). DCspecific ICAM-3-grabbing nonintegrin (DC-SIGN) is a C-type lectin receptor (CLR) that can bind to mannose and other sugars commonly expressed on the surfaces of a range of viruses (Drickamer, 1992). DC-SIGN plays both a positive and a negative role in immune regulation (Svajger et al, 2010). DC-SIGN has been reported to recognize mannose and fucose on the surfaces of viruses such as HIV-1 and SARS and to mediate viral immune evasion by DCs (Alen et al, 2009; Hoorelbeke et al, 2011)
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