Identification of DC-SIGN as the receptor during the interaction of Lactobacillus plantarum CGMCC 1258 and dendritic cells

Effects of Dietary Supplementation with Lactobacillus acidophilus and Bacillus subtilis on Mucosal Immunity and Intestinal Barrier Are Associated with Its Modulation of Gut Metabolites and Microbiota in Late-Phase Laying Hens

We investigated the effects of dietary supplementation with Lactobacillus acidophilus and Bacillus subtilis on the intestinal immune response, intestinal barrier function, cecal microbiota profile, and metabolite profile in late-phase laying hens. Hens were divided into three groups and fed with the basal diet (NC group), basal diet supplementation with 250 mg/kg B. subtilis and L. acidophilus mixture powder (LD group), and basal diet supplementation with 500 mg/kg B. subtilis and L. acidophilus mixture powder (HD group), respectively. The results indicated that the dietary supplementation with L. acidophilus and B. subtilis increased the integrity of the intestinal barrier as evidenced by the significant increase in the number of ileal goblet cells and improve the expression of occludin, claudin-1, and ZO-1 genes in the HD group. Moreover, the levels of IL-6, TNF-α, and IFN-γ were significantly decreased in the LD and HD groups. The levels of immunoglobulin G (IgG) increased in the LD and HD group, and the levels of secretory immunoglobulin A (sIgA) increased with the HD treatment. Furthermore, 16 s rRNA sequencing revealed L. acidophilus in combination with B. subtilis increased the diversity of gut microbiota. The metabolomic analysis revealed beneficial changes in the amino acid metabolism and lipid metabolism (decrease in LysoPC and LysoPE levels). In conclusion, dietary supplementation with L. acidophilus and B. subtilis could improve intestinal barrier function and maintain immune homeostasis. These beneficial effects may be associated with the modulation of the intestinal microbiome and metabolites.

Immunostimulation by Lactobacillus kefiri S-layer proteins with distinct glycosylation patterns requires different lectin partners

S-layer (glyco)-proteins (SLPs) form a nanostructured envelope that covers the surface of different prokaryotes and show immunomodulatory activity. Previously, we have demonstrated that the S-layer glycoprotein from probiotic Lactobacillus kefiri CIDCA 8348 (SLP-8348) is recognized by Mincle (macrophage inducible C-type lectin receptor), and its adjuvanticity depends on the integrity of its glycans. However, the glycan's structure has not been described so far. Herein, we analyze the glycosylation pattern of three SLPs, SLP-8348, SLP-8321, and SLP-5818, and explore how these patterns impact their recognition by C-type lectin receptors and the immunomodulatory effect of the L. kefiri SLPs on antigen-presenting cells. High-performance anion-exchange chromatography-pulse amperometric detector performed after β-elimination showed glucose as the major component in the O-glycans of the three SLPs; however, some differences in the length of hexose chains were observed. No N-glycosylation signals were detected in SLP-8348 and SLP-8321, but SLP-5818 was observed to have two sites carrying complex N-glycans based on a site-specific analysis and a glycomic workflow of the permethylated glycans. SLP-8348 was previously shown to enhance LPS-induced activation on both RAW264.7 macrophages and murine bone marrow-derived dendritic cells; we now show that SLP-8321 and SLP-5818 have a similar effect regardless of the differences in their glycosylation patterns. Studies performed with bone marrow-derived dendritic cells from C-type lectin receptor-deficient mice revealed that the immunostimulatory activity of SLP-8321 depends on its recognition by Mincle, whereas SLP-5818's effects are dependent on SignR3 (murine ortholog of human DC-SIGN). These findings encourage further investigation of both the potential application of these SLPs as new adjuvants and the protein glycosylation mechanisms in these bacteria.

S-Layer Glycoprotein From Lactobacillus kefiri Exerts Its Immunostimulatory Activity Through Glycan Recognition by Mincle

The development of new subunit vaccines has promoted the rational design of adjuvants able to induce a strong T-cell activation by targeting specific immune receptors. The S-layer is a (glyco)-proteinaceous envelope constituted by subunits that self-assemble to form a two-dimensional lattice that covers the surface of different species of Bacteria and Archaea. Due to their ability to self-assemble in solution, they are attractive tools to be used as antigen/hapten carriers or adjuvants. Recently, we have demonstrated that S-layer glycoprotein from Lactobacillus kefiri CIDCA 8348 (SLP-8348) enhanced the LPS-induced response on macrophages in a Ca²⁺-dependent manner, but the receptors involved in these immunomodulatory properties remain unknown. Therefore, we aim to determine the C-type lectin receptors (CLRs) recognizing this bacterial surface glycoprotein as well as to investigate the role of glycans in both the immunogenicity and adjuvant capacity of SLP-8348. Here, using a mild periodate oxidation protocol, we showed that loss of SLP-8348 glycan integrity impairs the cell-mediated immune response against the protein. Moreover, our data indicate that the adjuvant capacity of SLP-8348 is also dependent of the biological activity of the SLP-8348 glycans. In order to evaluate the CLRs involved in the interaction with SLP-8348 an ELISA-based method using CLR–hFc fusion proteins showed that SLP-8348 interacts with different CLRs such as Mincle, SingR3, and hDC-SIGN. Using BMDCs derived from CLR-deficient mice, we show that SLP-8348 uptake is dependent of Mincle. Furthermore, we demonstrate that the SLP-8348-induced activation of BMDCs as well as its adjuvant capacity relies on the presence of Mincle and its signaling adaptor CARD9 on BMDCs, since SLP-8348-activated BMDCs from Mincle^−/− or CARD9^−/− mice were not capable to enhance OVA-specific response in CD4⁺ T cells purified from OT-II mice. These findings significantly contribute to the understanding of the role of glycans in the immunomodulation elicited by bacterial SLPs and generate a great opportunity in the search for new adjuvants derived from non-pathogenic microorganisms.

Lactobacillus plantarum NCU116 Attenuates Cyclophosphamide-Induced Immunosuppression and Regulates Th17/Treg Cell Immune Responses in Mice

The balance of T helper cells 17 (Th17)/regulatory T cells (Treg) plays a key role in maintaining a normal immune response. It is well-known that cyclophosphamide (CTX) applied at high dose often damages the immune system by inhibiting immune cell proliferation. In this study, the immunomodulating effects of Lactobacillus plantarum NCU116 in CTX-induced immunosuppression mice were investigated. Results showed that the levels of cytokines interleukin (IL)-17 and IL-21 were significantly increased after 10 days of treatment with a high dose of NCU116 (46.92 ± 4.28 and 119.92 ± 10.89, respectively) compared with the model group (36.20 ± 2.63, 61.00 ± 6.92, respectively), and the levels of cytokines IL-23 and TGF-β3 of the three NCU116 treatment groups were significantly higher than that of the model group (90.48 ± 6.33 and 140.45 ± 14.30, respectively) (p < 0.05) and close to 62 and 69% of the normal group's level (140.98 ± 14.74 and 266.95 ± 23.11, respectively) at 10 days. The bacterium was also found to increase the expression levels of Th17 immune response and Treg immune response specific transcription factors RORγt and Foxp3. In addition, the bacterium significantly increased the number of CD4(+)T cells and dendrtic cells (DCs) and up-regulated mRNA expression of Toll-like receptors (TLRs). These findings demonstrated that NCU116 has the potential ability to enhance intestinal mucosa immunity and regulate the Th17/Treg balance, which may be attributed to the TLR pathway in DCs.

Knockout of MIMP protein in lactobacillus plantarum lost its regulation of intestinal permeability on NCM460 epithelial cells through the zonulin pathway

BACKGROUND

Previous studies indicated that the micro integral membrane protein located within the media place of the integral membrane protein of Lactobacillus plantarum CGMCC 1258 had protective effects against the intestinal epithelial injury. In our study, we mean to establish micro integral membrane protein -knockout Lactobacillus plantarum (LPKM) to investigate the change of its protective effects and verify the role of micro integral membrane protein on protection of normal intestinal barrier function.

METHODS

Binding assay and intestinal permeability were performed to verify the protective effects of micro integral membrane protein on intestinal permeability in vitro and in vivo. Molecular mechanism was also determined as the zonulin pathway. Clinical data were also collected for further verification of relationship between zonulin level and postoperative septicemia.

RESULTS

LPKM got decreased inhibition of EPEC adhesion to NCM460 cells. LPKM had lower ability to alleviate the decrease of intestinal permeability induced by enteropathogenic-e.coli, and prevent enteropathogenic-e.coli -induced increase of zonulin expression. Overexpression of zonulin lowered the intestinal permeability regulated by Lactobacillus plantarum. There was a positive correlation between zonulin level and postoperative septicemia. Therefore, micro integral membrane protein could be necessary for the protective effects of Lactobacillus plantarum on intestinal barrier.

CONCLUSION

MIMP might be a positive factor for Lactobacillus plantarum to protect the intestinal epithelial cells from injury, which could be related to the zonulin pathway.

Involvement of the mannose receptor and p38 mitogen-activated protein kinase signaling pathway of the microdomain of the integral membrane protein after enteropathogenic Escherichia coli infection

The microdomain of the integral membrane protein (MIMP) has been shown to adhere to mucin and to antagonize the adhesion of enteropathogenic Escherichia coli (EPEC) to epithelial cells; however, the mechanism has not been fully elucidated. In this study, we further identified the receptor of MIMP on NCM460 cells and investigated the mechanism (the p38 mitogen-activated protein kinase [MAPK] pathway) following the interaction of MIMP and its corresponding receptor, mannose receptor. We first identified the target receptor of MIMP on the surfaces of NCM460 cells using immunoprecipitation-mass spectrometry technology. We also verified the mannose receptor and examined the degradation and activation of the p38 MAPK signaling pathway. The results indicated that MIMP adhered to NCM460 cells by binding to the mannose receptor and inhibited the phosphorylation of p38 MAPK stimulated after EPEC infection via inhibition of the Toll-like receptor 5 pathway. These findings indicated that MIMPs relieve the injury of NCM460 cells after enteropathogenic E. coli infection through the mannose receptor and inhibition of the p38 MAPK signaling pathway, both of which may therefore be potential therapeutic targets for intestinal diseases, such as inflammatory bowel disease.

Lactobacillus plantarum surface layer adhesive protein protects intestinal epithelial cells against tight junction injury induced by enteropathogenic Escherichia coli

Lactobacillus plantarum (LP) has previously been used for the treatment and prevention of intestinal disorders and disease. However, the role of the LP surface layer adhesive protein (SLAP) in inhibition of epithelial cell disruption is not fully understood. The aim of the present study was to investigate the protective effects of purified SLAP on Caco-2 cells infected with enteropathogenic Escherichia coli (EPEC). The role of ERK in LP-mediated inhibition of tight junction (TJ) injury was also evaluated in order to determine the molecular mechanisms underlying the protective effects of LP in epithelial cells. SLAP was extracted and purified from LP cells using a porcine stomach mucin-Sepharose 4B column. SLAP-mediated inhibition of bacterial adhesion was measured using a competition-based adhesion assay. Expression of TJ-associated proteins, maintenance of TJ structure, and levels of extracellular signal regulated kinase (ERK) and ERK phosphorylation were assessed in SLAP-treated cells by a combination of real-time PCR, western blotting, and immunofluorescence microscopy. Cell permeability was analyzed by measurement of trans-epithelial electrical resistance (TER) and dextran permeability. The effect of SLAP on levels of apoptosis in epithelial cells was assessed by flow cytometry. Results from these experiments revealed that treatment with SLAP decreased the level of adhesion of EPEC to Caco-2 cells. SLAP treatment also enhanced expression of TJ proteins at both the mRNA and protein levels and affected F-actin distribution. Although ERK levels remained unchanged, ERK phosphorylation was increased by SLAP treatment. Caco-2 cells treated with SLAP exhibited increased TER and decreased macromolecular permeability, which was accompanied by a decrease in the level of apoptosis. Together, these results suggest that LP-produced SLAP protects intestinal epithelial cells from EPEC-induced injury, likely through a mechanism involving ERK activation.