Antitumor activity of lipopolysaccharide and radio-detoxified lipopolysaccharide of Vibrio parahaemolyticus

The Role of Plasmacytoid Dendritic Cells in Cancers

Plasmacytoid dendritic cells (pDCs) are a special subtype of dendritic cells with the morphology of plasma cells. pDCs produce massive amounts of type I interferon (IFN-I), which was originally found to play an extremely pivotal role in antiviral immunity. Interestingly, accumulated evidence indicates that pDCs can also play an important role in tumorigenesis. In the human body, most of the IFN-α is secreted by activated pDCs mediated by toll-like receptor (TLR) stimulation. In many types of cancer, tumors are infiltrated by a large number of pDCs, however, these pDCs exhibit no response to TLR stimulation, and reduced or absent IFN-α production. In addition, tumor-infiltrating pDCs promote recruitment of regulatory T cells (Tregs) into the tumor microenvironment, leading to immunosuppression and promoting tumor growth. In this review, we discuss recent insights into the development of pDCs and their roles in a variety of malignancies, with special emphasis on the basic mechanisms.

Th17 activation by dendritic cells stimulated with gamma-irradiated Streptococcus pneumoniae

Dendritic cells (DCs) play an important role in antigen presentation, which is an essential step for the induction of antigen-specific adaptive immunity. Inactivated bacterial whole cell vaccines have been widely used to prevent many bacterial infections because they elicit good immunogenicity due to the presence of various antigens and are relatively inexpensive and easy to manufacture. Recently, gamma-irradiated whole cells of nonencapsulated Streptococcus pneumoniae were developed as a broad-spectrum and serotype-independent multivalent vaccine. In the present study, we generated gamma-irradiated S. pneumoniae (r-SP) and investigated its capacity to stimulate mouse bone marrow-derived DCs (BM-DCs) in comparison with heat-inactivated and formalin-inactivated S. pneumoniae (h-SP and f-SP, respectively). r-SP showed an attenuated binding and internalization level to BM-DCs when compared to h-SP or f-SP. r-SP weakly induced the expression of CD80, CD83, CD86, MHC class I, and PD-L2 compared with h-SP or f-SP. Furthermore, r-SP less potently induced IL-6, TNF-α, and IL-23 expression than h-SP or f-SP but more potently induced IL-1β expression than h-SP or f-SP in BM-DCs. Since Th17-mediated immune responses are known to be important for the protection against pneumococcal infections, r-SP-primed DCs were co-cultured with splenocytes or splenic CD4⁺ T cells. Interestingly, r-SP-sensitized BM-DCs markedly induced IL-17A⁺ CD4⁺ T cells whereas h-SP- or f-SP-sensitized BM-DCs weakly induced them. Collectively, these results suggest that r-SP could be an effective pneumococcal vaccine candidate eliciting Th17-mediated immune responses by stimulation of DCs.

Characterization of Chemically-Induced Bacterial Ghosts (BGs) Using Sodium Hydroxide-Induced Vibrio parahaemolyticus Ghosts (VPGs)

Acellular bacterial ghosts (BGs) are empty non-living bacterial cell envelopes, commonly generated by controlled expression of the cloned lysis gene E of bacteriophage PhiX174. In this study, Vibrio parahaemolyticus ghosts (VPGs) were generated by chemically-induced lysis and the method is based on minimum inhibitory concentration (MIC) of sodium hydroxide (NaOH), acetic acid, boric acid, citric acid, maleic acid, hydrochloric acid, and sulfuric acid. The MIC values of the respective chemicals were 3.125, 6.25, <50.0, 25.0, 6.25, 1.56, and 0.781 mg/mL. Except for boric acid, the lysis efficiency reached more than 99.99% at 5 min after treatment of all chemicals. Among those chemicals, NaOH-induced VPGs appeared completely DNA-free, which was confirmed by quantitative real-time PCR. Besides, lipopolysaccharides (LPS) extracted from the NaOH-induced VPGs showed no distinctive band on SDS-PAGE gel after silver staining. On the other hand, LPS extracted from wild-type bacterial cells, as well as the organic acids-induced VPGs showed triple major bands and LPS extracted from the inorganic acids-induced VPGs showed double bands. It suggests that some surface structures in LPS of the NaOH-induced VPGs may be lost, weakened, or modified by the MIC of NaOH. Nevertheless, Limulus amoebocyte lysate assay revealed that there is no significant difference in endotoxic activity between the NaOH-induced VPGs and wild-type bacterial cells. Macrophages exposed to the NaOH-induced VPGs at 0.5 × 10⁶ CFU/mL showed cell viability of 97.9%, however, the MIC of NaOH did not reduce the cytotoxic effect of wild-type bacterial cells. Like Escherichia coli LPS, the NaOH-induced VPGs are an excellent activator of pro-inflammatory cytokines (IL-1β and iNOS), anti-inflammatory cytokine (IL-10), and dual activities (IL-6) in the stimulated macrophage cells. On the other hand, the induction of TNF-α mRNA was remarkable in the macrophages exposed with wild-type cells. Scanning electron microscopy showed the formation of trans-membrane lysis tunnel structures in the NaOH-induced VPGs. SDS-PAGE and agarose gel electrophoresis also confirmed that cytoplasmic proteins and genomic DNA released from the VPGs to culture medium through the lysis tunnel structures. Taken together, all these data indicate that the NaOH-induced VPGs show the potency of a safe, economical, and effective inactivated bacterial vaccine candidate.

Induction of antigen-specific Th1-type immune responses by gamma-irradiated recombinant Brucella abortus RB51

Brucella abortus strain RB51 is an attenuated rough mutant used as the live vaccine against bovine brucellosis in the United States and other countries. We previously reported the development of strain RB51 as a bacterial vaccine vector for inducing Th1-type immune responses against heterologous proteins. Because safety concerns may preclude the use of strain RB51-based recombinant live vaccines, we explored the ability of a gamma-irradiated recombinant RB51 strain to induce heterologous antigen-specific immune responses in BALB/c mice. Exposure of strain RB51G/LacZ expressing Escherichia coli beta-galactosidase to a minimum of 300 kilorads of gamma radiation resulted in complete loss of replicative ability. These bacteria, however, remained metabolically active and continued to synthesize beta-galactosidase. A single intraperitoneal inoculation of mice with 10(9) CFU equivalents of gamma-irradiated, but not heat-killed, RB51G/LacZ induced a beta-galactosidase-specific Th1-type immune response. Though no obvious differences were detected in immune responses to B. abortus-specific antigens, mice vaccinated with gamma-irradiated, but not heat-killed, RB51G/LacZ developed significant protection against challenge with virulent B. abortus. In vitro experiments indicated that gamma-irradiated and heat-killed RB51G/LacZ induced maturation of dendritic cells; however, stimulation with gamma-irradiated bacteria resulted in more interleukin-12 secretion. These results suggest that recombinant RB51 strains exposed to an appropriate minimum dose of gamma radiation are unable to replicate but retain their ability to stimulate Th1 immune responses against the heterologous antigens and confer protection against B. abortus challenge in mice.

Characterization of new O3:K6 strains and phylogenetically related strains of Vibrio parahaemolyticus isolated in Taiwan and other countries

AIMS

We analysed the genetic divergence in the pandemic new O3:K6 and phylogenetically related (new O3:K6-like) strains and compare these two groups in terms of virulence and other biological traits.

METHODS AND RESULTS

A total of 160 new O3:K6, new O3:K6-like and other strains of Vibrio parahaemolyticus isolated in Taiwan and other countries were collected and their clonal relationships analysed using SfiI-pulsed-field gel electrophoresis. All of the new O3:K6 and new O3:K6-like strains were grouped in cluster I with five new patterns identified. A O6:K18 strain was identified as a new member of the new O3:K6-like strains in addition to O4:K68, O1:KUT and O1:K25 strains. All of the lipopolysaccharide preparations of the selected strains exhibited closely spaced quadruplet banding patterns with similar mobility. The two groups of strains exhibited 100% sequence identity in the internal sequences of the toxR and laf genes, and also displayed similar virulence properties as determined with a suckling mouse model.

CONCLUSIONS

The new O3:K6 and new O3:K6-like strains were highly similar in virulence and in several other phenotypical and genotypical traits.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrated the spread and divergence of the pandemic and related clone of V. parahaemolyticus with similar virulence.

Electrophoretic and chemical characterization of lipopolysaccharides of Vibrio parahaemolyticus

Lipopolysaccharides (LPSs) isolated from three Kanagawa-positive and three negative strains of Vibrio parahaemolyticus were characterized by using electrophoretic, immunochemical, and chemical methods. The results of this study indicated that the LPSs of all six strains of V. parahaemolyticus examined did not have an O-specific side chain. These V. parahaemolyticus LPSs appeared to have molecular weights similar to that of the rough-type (Ra) LPS of Salmonella typhimurium TV-119 and might just contain lipid A and a core region. However, the microheterogeneity of V. parahaemolyticus LPS observed was greater than that of S. typhimurium LPS. The profile of V. parahaemolyticus LPS consisted of closely spaced triplet or quadruplet bands, but that of S. typhimurium consisted of doublet bands. Slower-moving bands appeared on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels only when large amounts of V. parahaemolyticus LPS were loaded. These bands were proven to be the aggregates of the fastest-moving low-molecular-weight bands by re-electrophoresis. The banding pattern of V. parahaemolyticus LPSs produced on nitrocellulose membranes by immunoblotting indicated that the V. parahaemolyticus LPSs did not have an O-specific side chain. The low ratio of total carbohydrate to lipid A of V. parahaemolyticus LPSs also suggested that they were like rough-type LPS. The mobility and profile of V. parahaemolyticus LPS on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel and its chemical composition were closely related to the serotype of a specific strain but not with the Kanagawa phenomenon.

Biological activities of lipid A from Vibrio parahaemolyticus: stimulation of murine peritoneal macrophages

The toxicity and macrophage stimulating property of Vibrio parahaemolyticus lipid A was studied. The LD50 dose of lipid A in galactosamine-sensitized mice was found to be 0.6 micrograms when injected intraperitoneally. Administration of lipid A resulted in stimulation of peritoneal macrophages as evident by increase in their cellular RNA contents and lysosomal enzyme activities. The treatment also caused enhancement in the phagocytic activity of macrophages.