The Outer Membrane Vesicles of Salmonella enterica Serovar Typhimurium Activate Chicken Immune Cells through Lipopolysaccharides and Membrane Proteins.

Hongxiao Cui,Hua Lin,Xin Zhao,Yajun Sun,Yan Zhao

doi:10.3390/pathogens11030339

Abstract

Salmonella is a common pathogen which can secrete outer membrane vesicles (OMVs). However, the effect of OMVs from Salmonella enterica Serovar Typhimurium (S. Typhimurium) of poultry origin on cells of the chicken innate immune system is not well known. In this study, S. Typhimurium OMVs were first isolated from three different poultry strains of Salmonella, Salmonella CVCC542, SALA, and SALB. In order to investigate the effect of OMVs on the maturation of monocytes into macrophages, both bone marrow-derived (BMD) monocytes and macrophage cell line HD11 cells were used. OMVs promoted the formation of monocyte dendrites in both types of cells, enabled BMD cells to become larger, and stimulated expression of LPS-induced TNF-αfactor (LITAF), IL-6, and inducible nitric oxide synthase (iNOS) genes in HD11 cells. These results demonstrated the capability of OMVs to promote the development of chicken monocytes into macrophages and the maturation of macrophages. In order to study the effect of OMVs on the phagocytosis of macrophages, chicken spleen-derived monocytes and HD11 cells were used. Phagocytosis of FITC-Salmonella and FITC-dextran by these two types of cells was enhanced after stimulation with OMVs. To determine which components in OMVs were responsible for the above observed results, OMVs were treated with proteinase K(PK) or polymyxin B (PMB). Both treatments reduced the phagocytosis of FITC-Salmonella by HD11 cells and chicken spleen mononuclear cells and reduced the secretion of IL-1β, LITAF, and IL-6 cytokines. These results demonstrated that Salmonella OMVs activated chicken macrophages and spleen mononuclear cells and the activation was achieved mainly through lipopolysaccharides and membrane proteins.

Highlights

Salmonella-induced foodborne illness is a serious problem for global public health
Compared with the outer membrane vesicles (OMVs) + PK group, the OMVs + polymyxin B (PMB) group significantly reduced the secretion of IL-1β and LITAF in the cell supernatant. These results indicated that reduction of the proteins or LPS in OMVs affected the immunomodulatory effect of OMVs on HD11, especially after inhibiting LPS
Compared with the OMVs + PK group, the OMVs + PMB group significantly reduced the phagocytic activity for fluorescein isothiocyanate (FITC)-Salmonella (Figure 7A), FITCStaphylococcus aureus (Figure 7C), and FITC-dextran (Figure 7D) in HD11. These results indicated that both LPS and proteins in OMVs could enhance the phagocytic activities of chicken macrophages HD11

Summary

Introduction

Salmonella-induced foodborne illness is a serious problem for global public health. The major sources of human salmonellosis are contaminated poultry-derived food products, mainly eggs and chicken meat. Using outbreak data up to 2019, the Interagency Food Safety Analytics Collaboration (2021) estimated that around 23.1% of foodborne salmonellosis in the United States was traceable to chickens and eggs [1]. Preventing and reducing Salmonella infection in poultry can improve poultry health and reduce salmonellosis in humans. Many effective management measures have been developed to control Salmonella infection on poultry farms, mainly using sanitary barrier and immune strategies. Live-attenuated vaccines, inactivated vaccines, and subunit vaccines have been developed for Salmonella, with various degrees of success [2]. In addition to stimulating the immune system to prevent pathogens from causing disease, oral administration of an attenuated Salmonella enterica Serovar Typhimurium OMVs possess a series of surface antigens with natural conformation and natural properties (such as immunogenicity, self-adjuvant, and immune cell absorption) and can be attractive vaccines against pathogenic bacteria [4]. Neisseria meningitidis OMV vaccines (“Bexsero”) have been approved by the Food and Drug Administration to prevent group B Neisseria meningitidis in the United States [8]

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