VscF in T3SS1 Helps to Translocate VPA0226 in Vibrio parahaemolyticus

In Vibrio parahaemolyticus, type III secretion system 1 (T3SS1) is a major virulence factor that delivers effectors into the host eukaryotic cytoplasm; however, studies on its infection mechanism are currently limited. To determine the function of the vscF gene, we constructed the vscF deletion mutant ΔvscF and complementation strain CΔvscF. Compared with those of wild-type POR-1 and CΔvscF, the cytotoxic, adherent, and apoptotic abilities of ΔvscF in HeLa cells were significantly reduced (P < 0.01). Furthermore, in infected HeLa cells, the mutant strain reduced the translocation rates of VP1683 and VP1686 effectors compared to the wild-type and complementation strains. A BLAST search showed that vscF is homologous to the MixH needle protein of Shigella flexneri, indicating that the vscF gene encodes the needle protein of T3SS1 in V. parahaemolyticus. Additional translocation assays showed that VPA0226 translocated into the HeLa eukaryotic cytoplasm via T3SS1, secretion assays showed that VPA0226 can be secreted to supernatant by T3SS1, indicating that VPA0226 belongs to the unpublished class of T3SS1 effectors. In conclusion, our data indicate an essential role of vscF in V. parahaemolyticus T3SS1 and revealed that VPA0226 can be secreted into the host cell cytoplasm via T3SS1. This study provides insights into a previously unexplored aspect of T3SS1, which is expected to contribute to the understanding of its infection mechanism.

Quercetin attenuates the production of pro-inflammatory cytokines in H292 human lung epithelial cells infected with Pseudomonas aeruginosa, by modulating ExoS production

Background: The type three secretion system (T3SS) is a major virulence system of Pseudomonas aeruginosa (P. aeruginosa). The effector protein Exotoxin S (ExoS) produced by P. aeruginosa is secreted into the host cells via the T3SS. For the purpose of screening the inhibitors with regard to ExoS secretion, we developed the sandwich-type enzyme-linked immunosorbent assay (ELISA) system. From the initial screening, quercetin was selected because it has the prominent effect of ExoS inhibition and also is known to have anti-inflammatory and antioxidant effects on mammalian cells.Results: In this study, we investigated the effects of quercetin on the expression and secretion of ExoS using the ELISA and Western blot analysis methods. The results showed that the secretion of ExoS was significantly decreased by 10, 20uM quercetin. Also, pscF and popD, which are composed of the T3SS needle, are reduced by quercetin at the mRNA level, and we confirmed the inhibitory effect of quercetin on cytokines in P. aeruginosa-infected H292 cells by real-time polymerase chain reaction (PCR). Conclusion: Collectively, quercetin inhibits the secretion of ExoS by reducing both ExoS production and the expression of the needle protein of T3SS. Furthermore, these results suggest that quercetin has the potential to be used as an anti-toxic treatment for the disease caused by P. aeruginosa infection.

Broad detection of bacterial type III secretion system and flagellin proteins by the human NAIP/NLRC4 inflammasome

Inflammasomes are cytosolic multiprotein complexes that initiate host defense against bacterial pathogens by activating caspase-1–dependent cytokine secretion and cell death. In mice, specific nucleotide-binding domain, leucine-rich repeat-containing family, apoptosis inhibitory proteins (NAIPs) activate the nucleotide-binding domain, leucine-rich repeat-containing family, CARD domain-containing protein 4 (NLRC4) inflammasome upon sensing components of the type III secretion system (T3SS) and flagellar apparatus. NAIP1 recognizes the T3SS needle protein, NAIP2 recognizes the T3SS inner rod protein, and NAIP5 and NAIP6 recognize flagellin. In contrast, humans encode a single functional NAIP, raising the question of whether human NAIP senses one or multiple bacterial ligands. Previous studies found that human NAIP detects both flagellin and the T3SS needle protein and suggested that the ability to detect both ligands was achieved by multiple isoforms encoded by the single humanNAIPgene. Here, we show that human NAIP also senses theSalmonellaTyphimurium T3SS inner rod protein PrgJ and that T3SS inner rod proteins from multiple bacterial species are also detected. Furthermore, we show that a single human NAIP isoform is capable of sensing the T3SS inner rod, needle, and flagellin. Our findings indicate that, in contrast to murine NAIPs, promiscuous recognition of multiple bacterial ligands is conferred by a single human NAIP.

Chlamydial Type III Secretion System Needle Protein Induces Protective Immunity againstChlamydia muridarumIntravaginal Infection

Chlamydia trachomatisimposes serious health problems and causes infertility. Because of asymptomatic onset, it often escapes antibiotic treatment. Therefore, vaccines offer a better option for the prevention of unwanted inflammatory sequelae. The existence of serologically distinct serovars ofC. trachomatissuggests that a vaccine will need to provide protection against multiple serovars.Chlamydiaspp. use a highly conserved type III secretion system (T3SS) composed of structural and effector proteins which is an essential virulence factor. In this study, we expressed the T3SS needle protein ofChlamydia muridarum,TC_0037, an ortholog ofC. trachomatisCdsF, in a replication-defective adenoviral vector (AdTC_0037) and evaluated its protective efficacy in an intravaginalChlamydia muridarummodel. For better immune responses, we employed a heterologous prime-boost immunization protocol in which mice were intranasally primed with AdTC_0037 and subcutaneously boosted with recombinant TC_0037 and Toll-like receptor 4 agonist monophosphoryl lipid A mixed in a squalene nanoscale emulsion. We found that immunization with TC_0037 antigen induced specific humoral and T cell responses, decreasedChlamydialoads in the genital tract, and abrogated pathology of upper genital organs. Together, our results suggest that TC_0037, a highly conserved chlamydial T3SS protein, is a good candidate for inclusion in aChlamydiavaccine.

A Replication-Defective Human Type 5 Adenovirus-Based Trivalent Vaccine Confers Complete Protection against Plague in Mice and Nonhuman Primates

Currently, no plague vaccine exists in the United States for human use. The capsular antigen (Caf1 or F1) and two type 3 secretion system (T3SS) components, the low-calcium-response V antigen (LcrV) and the needle protein YscF, represent protective antigens ofYersinia pestis. We used a replication-defective human type 5 adenovirus (Ad5) vector and constructed recombinant monovalent and trivalent vaccines (rAd5-LcrV and rAd5-YFV) that expressed either the codon-optimizedlcrVor the fusion gene designatedYFV(consisting ofycsF,caf1, andlcrV). Immunization of mice with the trivalent rAd5-YFV vaccine by either the intramuscular (i.m.) or the intranasal (i.n.) route provided protection superior to that with the monovalent rAd5-LcrV vaccine against bubonic and pneumonic plague when animals were challenged withY. pestisCO92. Preexisting adenoviral immunity did not diminish the protective response, and the protection was always higher when mice were administered one i.n. dose of the trivalent vaccine (priming) followed by a single i.m. booster dose of the purified YFV antigen. Immunization of cynomolgus macaques with the trivalent rAd5-YFV vaccine by the prime-boost strategy provided 100% protection against a stringent aerosol challenge dose of CO92 to animals that had preexisting adenoviral immunity. The vaccinated and challenged macaques had no signs of disease, and the invading pathogen rapidly cleared with no histopathological lesions. This is the first report showing the efficacy of an adenovirus-vectored trivalent vaccine against pneumonic plague in mouse and nonhuman primate (NHP) models.