DNA sequencing of the gene encoding Salmonella typhimurium-derived T-cell inhibitor (STI) and characterization of the gene product, cloned STI

Influence of Helicobacter pylori oncoprotein CagA in gastric cancer: A critical-reflective analysis

Gastric cancer is the fifth most common malignancy and third leading cancer-related cause of death worldwide. Helicobacter pylori is a Gram-negative bacterium that inhabits the gastric environment of 60.3% of the world’s population and represents the main risk factor for the onset of gastric neoplasms. CagA is the most important virulence factor in H. pylori, and is a translocated oncoprotein that induces morphofunctional modifications in gastric epithelial cells and a chronic inflammatory response that increases the risk of developing precancerous lesions. Upon translocation and tyrosine phosphorylation, CagA moves to the cell membrane and acts as a pathological scaffold protein that simultaneously interacts with multiple intracellular signaling pathways, thereby disrupting cell proliferation, differentiation and apoptosis. All these alterations in cell biology increase the risk of damaged cells acquiring pro-oncogenic genetic changes. In this sense, once gastric cancer sets in, its perpetuation is independent of the presence of the oncoprotein, characterizing a “hit-and-run” carcinogenic mechanism. Therefore, this review aims to describe H. pylori- and CagA-related oncogenic mechanisms, to update readers and discuss the novelties and perspectives in this field.

Pathogenesis and clinical management of Helicobacter pylori gastric infection

Helicobacter pylori (H. pylori) is a gram-negative bacterium that infects approximately 4.4 billion individuals worldwide. However, its prevalence varies among different geographic areas, and is influenced by several factors. The infection can be acquired by means of oral-oral or fecal-oral transmission, and the pathogen possesses various mechanisms that improve its capacity of mobility, adherence and manipulation of the gastric microenvironment, making possible the colonization of an organ with a highly acidic lumen. In addition, H. pylori presents a large variety of virulence factors that improve its pathogenicity, of which we highlight cytotoxin associated antigen A, vacuolating cytotoxin, duodenal ulcer promoting gene A protein, outer inflammatory protein and gamma-glutamyl transpeptidase. The host immune system, mainly by means of a Th1-polarized response, also plays a crucial role in the infection course. Although most H. pylori-positive individuals remain asymptomatic, the infection predisposes the development of various clinical conditions as peptic ulcers, gastric adenocarcinomas and mucosa-associated lymphoid tissue lymphomas. Invasive and non-invasive diagnostic methods, each of them with their related advantages and limitations, have been applied in H. pylori detection. Moreover, bacterial resistance to antimicrobial therapy is a major challenge in the treatment of this infection, and new therapy alternatives are being tested to improve H. pylori eradication. Last but not least, the development of effective vaccines against H. pylori infection have been the aim of several research studies.

Identification of salmonella pathogenicity island-2 type III secretion system effectors involved in intramacrophage replication of S. enterica serovar typhimurium: implications for rational vaccine design

Salmonella enterica serovars cause severe diseases in humans, such as gastroenteritis and typhoid fever. The development of systemic disease is dependent on a type III secretion system (T3SS) encoded by Salmonella pathogenicity island-2 (SPI-2). Translocation of effector proteins across the Salmonella-containing vacuole, via the SPI-2 T3SS, enables bacterial replication within host cells, including macrophages. Here, we investigated the contribution of these effectors to intramacrophage replication of Salmonella enterica serovar Typhimurium using Fluorescence Dilution, a dual-fluorescence tool which allows direct measurement of bacterial replication. Of 32 strains, each carrying single mutations in genes encoding effectors, 10 (lacking sifA, sseJ, sopD2, sseG, sseF, srfH, sseL, spvD, cigR, or steD) were attenuated in replication in mouse bone marrow-derived macrophages. The replication profiles of strains combining deletions in effector genes were also investigated: a strain lacking the genes sseG, sopD2, and srfH showed an increased replication defect compared to single-mutation strains and was very similar to SPI-2 T3SS-deficient bacteria with respect to its replication defect. This strain was substantially attenuated in virulence in vivo and yet retained intracellular vacuole integrity and a functional SPI-2 T3SS. Moreover, this strain was capable of SPI-2 T3SS-mediated delivery of a model antigen for major histocompatibility complex (MHC) class I-dependent T-cell activation. This work establishes a basis for the use of a poly-effector mutant strain as an attenuated vaccine carrier for delivery of heterologous antigens directly into the cytoplasm of host cells.

Live attenuated strains of Salmonella enterica serotype Typhi have generated much interest in the search for improved vaccines against typhoid fever and as vaccine vectors for the delivery of heterologous antigens. A promising vaccine candidate is the ΔaroC ΔssaV S. Typhi strain, which owes its attenuation mainly to lack of a type III secretion system (SPI-2 T3SS). The SPI-2 T3SS is important for bacterial proliferation inside macrophages, but not all of the effectors involved in this process have been identified. Here, we show that 10 effectors of the related strain S. Typhimurium contribute to intracellular replication in macrophages. Moreover, we establish that a poly-effector mutant strain of S. Typhimurium can have a severe replication defect and maintain a functional SPI-2 T3SS, which can be exploited for delivery of heterologous antigens.

The role of probiotics and antibiotics in regulating mucosal inflammation

Antibiotic and probiotic agents have increasingly moved in the focus of basic and clinical research as well as clinical trials for IBD therapy. Both approaches modulate the intestinal flora, the former through eradication or reduction, the latter through establishment or increase of luminal bacteria. Although clinical trials provide proof of principle that both approaches can be therapeutically successfull, we just start to understand the mechanims and may get a first feeling for the potential and limitations of these "microbial" therapies. As basic research sets out to dissect the field using extensive efforts and new technologies, a more detailed exploration of the genetic, immune and microbial factors that govern the life-long crosstalk between host and intestinal flora is already opening new insight into general aspects of human immunology, immune regulation, IBD pathogenesis and therapy.

Rational design of Salmonella recombinant vaccines

Salmonella enterica is an important pathogen of animals and humans causing a variety of infectious diseases. The large number of cases of typhoid fever due to S. enterica serovar Typhi infections gives rise to the continuous need for improved vaccines against this life-threatening infection. However, S. enterica is also an interesting organism to act as a live attenuated carrier for the presentation of recombinant heterologous antigens. Comprehensive experimental studies have been performed and a detailed knowledge of the molecular mechanisms of important virulence factors is available. This allows the rationale design of improved Salmonella carrier strains and the development of novel strategies for the expression and presentation of recombinant antigens. Here, we review recent advances in generation of live attenuated Salmonella vaccines and discuss criteria for expression strategies of heterologous antigens by Salmonella carrier strains.

Salmonella inhibit T cell proliferation by a direct, contact-dependent immunosuppressive effect

Dendritic cells (DC) are of central importance in the initiation of T cell-mediated adaptive immunity because these professional phagocytes internalize, process, and present microbial antigens to T lymphocytes. T lymphocytes have a pivotal role in controlling and clearing infection with intracellular pathogens through cytokine production. T lymphocytes also can mediate direct lysis of infected cells or activate B and T cells. In this article, we report that DC, when cocultured with Salmonella, fail to efficiently stimulate T cells for proliferation. We show that the failure of T lymphocytes to respond to Salmonella-infected DC is not simply due to Salmonella-induced programmed DC death or interference with up-regulation of costimulatory molecules CD80 and CD86. We cocultured bacteria with purified T lymphocytes, and we demonstrate here that Salmonella have a direct, contact-dependent inhibitory effect on the T cells, even in the absence of DC. This direct, Salmonella-induced inhibitory effect reduces the ability of T cells to proliferate and produce cytokines in response to stimulation and appears to require live bacteria. Cumulatively, these results are evidence that Salmonella may interfere with the development of acquired immunity, providing insights into the complex nature of this host-pathogen interaction.

Cytokines in Salmonellosis

The recruitment and activation of phagocytic cells in infected tissues and the induction of T-cell- and B-cell-dependent acquired immunity are crucial for the control and resolution of Salmonella infections. These complex processes require the interaction of bacteria with a multitude of cell surface receptors and the controlled production of soluble mediators. The mechanisms of cytokine induction in response to Salmonella and the role of cytokine networks in Salmonella infections are the main foci of this review. Pathogen-associated molecular pattern receptors play an important role in recognition of bacteria by the host. Effective immunity against the bacterium therefore relies on the ability of the host to recruit phagocytes in the tissues and to enhance the antibacterial functions of these inflammatory cells. TNF-a, IFN-?, IL12, IL15, and IL18 are needed for the full expression of innate host resistance to Salmonella. The genes for mammalian cytokines can be cloned into suitable vectors and expressed in Salmonella as functional proteins. The in vivo production of cytokines by Salmonella carriers can have therapeutic applications and can modulate immune functions in the host. The possibility to modulate antigen-specific immune responses by expressing cytokines in Salmonella is illustrated by the increase in Salmonella-specific IgA responses induced by administration of IL-5-expressing bacteria. The same cytokines that are responsible for endotoxic shock are elevated in the late stages of lethal Salmonella infections, indicating that the toxicity of Salmonella lipopolysaccharide (LPS) may actually be contributing to the death of the host.

[Bacterial cyclostatin, or how do bacteria manipulate the eukaryotic cell cycle]

Several bacterial proteins have been recently described that share the ability to inhibit the proliferation of cells in culture without causing early signs of cytotoxicity. Such observations suggest the existence of bacterial mechanisms of control of the eukaryotic cell cycle contributing to pathogenicity or adaptation to the host. This emerging concept of cellular microbiology is critically analyzed considering as a model the cytolethal distending toxins (CDT), a family of toxins whose mode of action on the cell cycle has been thoroughly studied over the last few years. CDTs activate a physiological G2 checkpoint in exposed cells, probably from an initial DNA alteration whose precise molecular nature has not yet been determined. Experimental data are lacking to extrapolate in vivo the antiproliferative effect of these bacterial proteins that we tentatively propose to call cyclostatins.

Excess production of interleukin-12 subunit p40 stimulated by the virulence plasmid of Salmonella enterica serovar Typhimurium in the early phase of infection in the mouse

The production of interleukin-12 (IL-12) and its subunits in response to Salmonella enterica serovar Typhimurium infection in the BALB/c mouse was examined. Unlike wild-type Typhimurium, a plasmidless strain, isolated by curing of the virulence plasmid (pSTV), did not stimulate excess IL-12p40 production. When a Tn 5 tagged pSTV was transferred back to the plasmidless strain, the ability to stimulate IL-12p40 production was restored. However, a strain harbouring another Tn50pSTV failed to stimulate excess IL-12p40 production. This Tn 5 insertion area, located on fragment H3 of pSTV, was designated spf (stimulation of protein forty). The ability to stimulate IL-12p40 production was restored in a partial diploid that carried a wild-type fragment covering the spf site. There is one known gene, repA, a locus, rsk, and two putative ORFs, in the vicinity of the Tn 5 insertion site; however, these are not spf. The precise location of the spf locus is still unknown.