Purification and partial characterization of a product from Yersinia pseudotuberculosis with the ability to activate human T cells

[First case of lung abscess due to Yersinia pseudotuberculosis in Japan]

A 63-year-old previously healthy man was admitted to our hospital with diarrhea that had lasted for about 4 weeks, high fever and dyspnea. Chest computed tomography showed consolidation with a low-density area in the right middle lobe and small nodules with feeding vessels in the right upper lobe. On Day 8, a cavity was observed in the consolidation, and the lymph nodes in the mediastinum became necrotic. Yersinia pseudotuberculosis (serotype 4b) was cultured from blood, bronchial washing fluid, and lung tissue specimens. We diagnosed the lung lesions as septic pulmonary embolism caused by enterocolitis. We started treatment with tazobactam/piperacillin. It has been reported that high-dose ceftriaxone (CTRX) is effective, but CTRX at normal doses and other beta-lactams are less effective or even ineffective. Therefore, we changed to CTRX (4g/day) on Day 5, CTRX (2g/day) on Day 8, and oral cefditoren pivoxil (600 mg/day; a third-generation cephalosporin) on Day 18. Antibiotic therapy resulted in a favorable response. The patient was discharged from our hospital on day 25 in good health. To the best of our knowledge, this is the first case of a lung abscess caused by Y. pseudotuberculosis reported in Japan.

Crystal and Solution Structures of a Superantigen from Yersinia pseudotuberculosis Reveal a Jelly-Roll Fold

Superantigens are a class of microbial proteins with the ability to excessively activate T cells by binding to the T cell receptor. The staphylococcal and streptococcal superantigens are closely related in structure and possess an N-terminal domain that resembles an OB fold and a C-terminal domain similar to a beta-grasp fold. Yersinia pseudotuberculosis produces superantigens, YPMa, YPMb, and YPMc, which have no significant amino acid similarity to other proteins. We have determined the crystal and solution structures of YPMa, which show that the protein has a jelly-roll fold. The closest structural neighbors to YPMa are viral capsid proteins and members of the tumor necrosis factor superfamily. In the crystal structure, YPMa packs as a trimer, another feature shared with viral capsid proteins and TNF superfamily proteins. However, in solution YPMa behaves as a monomer, and any functional relevance of the trimer observed in the crystals is yet to be established.

Streptococcus dysgalactiae-derived mitogen (SDM), a novel bacterial superantigen: characterization of its biological activity and predicted tertiary structure

A mitogenic substance, designated Streptococcus dysgalactiae-derived mitogen (SDM), was purified from S. dysgalactiae culture supernatant, and the gene encoding the mitogen was cloned. Both native and recombinant SDM expressed in Escherichia coli significantly activated human V beta 1+ and V beta 23+ T cells in association with major histocompatibility complex (MHC) class II molecules on accessory cells, indicating that SDM possesses superantigenic properties. The sdm gene consists of two segments encoding a signal peptide and a mature 25 kDa protein composed of 212 amino acids. Three of 34 S. dysgalactiae strains but none of 28 Streptococcus pyogenes strains examined carried sdm. Phylogenetic analysis indicated that SDM belongs to a family distinct from established bacterial superantigens. SDM showed around 30% homology with other superantigens at the amino acid sequence level. The tertiary structure of SDM was predicted by modelling onto streptococcal pyrogenic exotoxin C and streptococcal mitogenic exotoxin Z-2, both of which share highly homologous structure-determining regions. SDM showed overall structural similarity to both these superantigens. This is the first study to characterize fully a bacterial superantigen from S. dysgalactiae.

Increased resistance in BALB/c mice to reinfection with Candida albicans is due to immunoneutralization of a virulence-associated immunomodulatory protein

Here, it is shown that immunoneutralization of p43, a virulence-associated immunomodulatory protein secreted by Candida albicans, is responsible for immunoprotection against candidiasis after spontaneous healing of mice inoculated with 10(6) C. albicans blastoconidia. p43 is produced by the pathogenic Candida blastoconidia, and neither immunoprotection nor immunoneutralization can be elicited by priming the mice with attenuated or heat-killed C. albicans blastoconidia. The immunoprotection against systemic candidiasis was positively correlated with (i). serum levels of antibodies against p43 and (ii). a high ratio between antibodies against p43 and antibodies against C. albicans structural antigens. Immunoprotection against candidiasis can be induced in mice primed with heat-killed C. albicans, after treatment of the animals with anti-p43 antibodies. The data described here provide a biological explanation for active immunoprotection achieved after spontaneous healing of infectious diseases, namely in candidiasis.

Superantigen YPMa exacerbates the virulence of Yersinia pseudotuberculosis in mice

Yersinia pseudotuberculosis, a gram-negative bacterium responsible for enteric and systemic infection in humans, produces a superantigenic toxin designated YPMa (Y. pseudotuberculosis-derived mitogen). To assess the role of YPMa in the pathogenesis of Y. pseudotuberculosis, we constructed a superantigen-deficient mutant and compared its virulence in a mouse model of infection to the virulence of the wild-type strain. Determination of the survival rate after intravenous (i.v.) bacterial inoculation of OF1 mice clearly showed that inactivation of ypmA, encoding YPMa, reduced the virulence of Y. pseudotuberculosis. Mice infected i.v. with 10(4) and 10(5) wild-type bacteria died within 9 days, whereas mice infected with the ypmA mutant survived 12 and 3 days longer, respectively. This decreased virulence of the ypmA mutant strain was not due to an impaired colonization of the spleen, liver, or lungs. In contrast to i.v. challenge, bacterial inoculation by the intragastric (i.g.) route did not reveal any difference in virulence between wild-type Y. pseudotuberculosis and the ypmA mutant since the 50% lethal doses were identical for both strains. Moreover, inactivation of ypmA gene did not affect the bacterial growth of Y. pseudotuberculosis in Peyer's patches, mesenteric lymph nodes (MLNs), and spleen after oral infection. Histological studies of spleen, liver, lungs, heart, Peyer's patches, and MLNs after i.v. or i.g. challenge with the wild type or the ypmA mutant did not reveal any feature that can be specifically related to YPMa. Our data show that the superantigenic toxin YPMa contributes to the virulence of Y. pseudotuberculosis in systemic infection in mice.

Comparison of gingival and peripheral blood T cells among patients with periodontitis suggests skewing of the gingival T cell antigen receptor V beta repertoire

The present study investigated the expression of different variable regions of T cell receptor beta-chain (V beta) among functional subsets of T cells, i.e. CD45RO+ (activated/memory), CD4+ and CD8+ in gingiva and peripheral blood of patients with periodontitis. Gingival tissue specimens (n = 25) and peripheral blood were procured from 18 patients with periodontitis during periodontal surgery or extraction. Single-cell suspensions of gingival tissues were made by enzymatic digestion. These cells were immunofluorescently labeled with a panel of monoclonal antibodies specific for 18 TCR V beta regions, in concert with markers for various T cell subsets. The cells were then analyzed with 3-color multivariate flow cytometry. Results demonstrated that a significantly higher proportion of T cells in gingiva expressed V beta 5.2 (0.0005), V beta 6 (0.0007) and V beta 9 (0.003) regions compared to those in peripheral blood. Comparison of CD45RO+ (activated/memory) and CD45RO- (naïve) subsets of gingival T cells revealed differences in the expression of TCR V beta regions. V beta 5.2 expression was significantly higher among CD45RO+ gingival T cells (p = 0.004), whereas V beta 14 expression was elevated among the CD45RO- subset relative to peripheral blood (p = 0.008). Analysis of TCR V beta region expression among CD4+ and CD8+ subsets did not reveal any statistically significant differences between gingiva and peripheral blood, although some V beta regions approached significance. Collectively, these results demonstrate that the T cell repertoire in the gingival compartment differs significantly from that in the peripheral blood. Furthermore, since the skewing of TCR V beta was observed among naïve, as well as activated/memory T cells, it is likely that both developmental and environmental factors are influential in shaping the gingival TCR repertoire in patients with periodontitis. Elucidation of the cause of the skewed expression of T cell receptors in gingiva can provide insights into the specificity of T cells in periodontitis.

Analysis of functional regions of YPM, a superantigen derived from gram-negative bacteria

The bacterial superantigens, staphylococcal enterotoxins and streptococcal pyrogenic exotoxins, are grouped in a family by the conservation of amino acid sequence and polypeptide folding patterns. In the case of Yersinia pseudotuberculosis-derived mitogen (YPM), however, there is no noticeable homology with this family, although many of the in vitro functional features conform to the criteria for a superantigen. To study the mode of action of YPM at the molecular level, we first generated a number of YPM point mutants with reduced T-cell proliferative activity using random mutagenesis and localized the amino acid positions involved in either major histocompatibility complex class II or T-cell receptor Vbeta-interaction. Plotting the elucidated positions on the hydrophilicity profile suggested that they reside mostly on the outer portion of the molecule. We also report that the two cysteines positioned almost at opposing ends of the YPM molecule are connected by an S-S bond the destruction of which causes fatal damage. Finally, we obtained evidence that YPM partially competes with staphylococcal enterotoxin E for human leukocyte antigen-DR binding. This raises the question of whether these different types of superantigens have acquired the same function by genetic convergence or originated from a common ancestral gene.

Analysis of the superantigen-producing ability of Yersinia pseudotuberculosis strains of various serotypes isolated from patients with systemic or gastroenteric infections, wildlife animals and natural environments

Yersinia pseudotuberculosis is a pathogen causing gastroenteritis as well as acute and systemic infections. This organism produces a superantigenic exotoxin, designated Y. pseudotuberculosis-derived mitogen (YPM). We consider this exotoxin to be the primary pathogen of the systemic type infection. In this study, we examined 101 Y. pseudotuberculosis strains isolated from various sources, patients with the systemic or the gastroenteric type of infections, wildlife animals and natural environments for the presence of the YPM gene and the production of YPM or other related superantigens. We found that all of the strains isolated from patients with systemic type infection carried the YPM gene and produced YPM. A certain proportion of the organisms isolated from patients with the gastroenteric type infection, wildlife animals or natural environments did not carry the YPM gene nor produced superantigens. These results suggest that YPM is involved in the pathogenesis of the systemic type of Y. pseudotuberculosis infection.

Purification, characterization and cloning of a novel variant of the superantigen Yersinia pseudotuberculosis-derived mitogen

The novel superantigen designated as Yersinia pseudotuberculosis-derived mitogen typeB (YPMb) was purified from the cell lysate of Y. pseudotuberculosis O:6 strain (R-104). Proliferative response of human peripheral blood mononuclear cells to the purified YPMb was detectable at a concentration of as low as 1 pg/ml, that is comparable to the previously documented YPM (YPMa). The Vbeta repertoire specificity (3, 9, 13.1 and 13.2) of YPMb was also the same as that of YPMa. A gene (ypmB) encoding YPMb was cloned and its nucleotide sequence was determined. The open reading frame (ORF 453 bp) of the ypmB encodes a protein with 150 amino acid residues, though the precursor protein of YPMa consists of 151 amino acid residues. There is a nucleotide sequence homology of 88.9% between ypmB and ypmA. The low homology in the downstream of the structural gene between ypmB and ypmA and the difference in the GC content in the ORF of ypmB and ypmA from that of the base usage of Y. pseudotuberculosis suggest that the ypm gene originates from another organism. The alignment of the amino acid sequences of mature proteins of YPMb and YPMa revealed that there is 83% homology (108 amino acid residues are identical). Between YPMa and YPMb, the central region is less homologous than the N- and C-terminal regions. Based on the functional similarity of two superantigen molecules, the less homology suggested that the central region is less important for the function of both YPM molecules.

Identification of murine T cells reactive with the bacterial superantigen Yersinia pseudotuberculosis-derived mitogen (YPM) and factors involved in YPM-induced toxicity in mice

We previously reported that Yersinia pseudotuberculosis-derived mitogen (YPM) acts as a superantigen to human T cells. In this study, we assessed the superantigenicity and toxicity of YPM using murine experimental models. YPM activated T cells to produce interleukin-2 in a major histocompatibility complex class II molecule-dependent manner. The T-cell blasts induced by YPM expressed T-cell receptor (TCR) beta-chain variable region (Vbeta)7, Vbeta8.1, Vbeta8.2 and Vbeta8.3. The injection of YPM into mice pre-sensitized with D-galactosamine induced lethal shock. This shock was blocked by the injection of monoclonal antibodies (mAbs) to CD4, TCR Vbeta7 plus Vbeta8, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), but not by injection to CD8 or unrelated Vbeta. These results indicate that YPM-induced shock requires the presence of CD4+ T cells bearing TCR Vbeta7 and Vbeta8, and that endogenous TNF-alpha and IFN-gamma mediate the lethal effects.

Identification of the functional region on the superantigen Yersinia pseudotuberculosis-derived mitogen responsible for induction of lymphocyte proliferation by using synthetic peptides

Yersinia pseudotuberculosis-derived mitogen (YPM) is the unique Gram-negative bacillary superantigen known. In order to identify the regions on the YPM molecule involved in its superantigenic activity, seven overlapping peptides of the entire YPM molecule were synthesized and tested to evaluate their effects on the YPM-induced proliferation of human peripheral blood lymphocytes. A peptide corresponding to the N-terminal amino acid sequence (1-23) was found to inhibit YPM-induced lymphocyte proliferation in a concentration-dependent manner. The N-terminal peptide was found to show no inhibition of the proliferation induced by the other superantigen (staphylococcal enterotoxin B) or the other T-cell mitogen pertussis toxin, indicating that the inhibition is specific to YPM-induced proliferation. Thus, we have identified the N-terminal region (1-23) of the YPM as one of the functional regions responsible for its superantigenic activity.

Characterization of human T-cell responses to Yersinia enterocolitica superantigen

We reported that antigenic preparations from Yersinia enterocolitica stimulate murine T cells in a manner consistent with that of superantigens. As a consequence we examined whether Y. enterocolitica antigenic preparations stimulate human T-cell cultures. Human T cells, enriched from peripheral blood lymphocytes, were stimulated to proliferate in the presence of Y. enterocolitica cytoplasmic and membrane preparations. This activity has also been shown to be sensitive to protease treatment, indicating the presence of a protein, and when separated by ion-exchange chromatography a single peak of activity is resolved. Furthermore, this proliferation was inhibited, in a dose-dependent manner, by the presence of antibodies directed against MHC class II antigens, indicating a requirement for these molecules. When these cells were stained with a panel of V beta-specific antibodies to determine if there was an enrichment of a particular V beta-bearing T-cell subset after stimulation, results indicate a significant enrichment of T cells bearing V beta 3, V beta 12, V beta 14, and V beta 17 over controls. Taken together, these data are consistent with a Y. enterocolitica product acting as a superantigen for human T cells.

Purification and characterization of a novel superantigen produced by a clinical isolate of Yersinia pseudotuberculosis

A superantigen designated as Yersinia pseudotuberculosis-derived mitogen (YPM) was purified in an equal manner from both the culture supernatant and cell lysate of a clinical isolate (KUR-1) of Y. pseudotuberculosis serotype 4b. A significant proliferative response of human peripheral blood mononuclear cells to purified YPM was detectable even at a concentration of 1 pg/ml. The N-terminal sequence of YPM which included 23 amino acid residues was determined, by automated Edman degradation, as Thr-Asp-Tyr-Asp-Asn-Thr-Leu-Asn-Ser-Ile-Pro-Ser-Leu-Arg-Ile-Pro-Asn-Il e-Ala-Thr-Tyr-Thr-Gly-. This sequence differed from not only all the, hitherto, reported superantigens but also known proteins. While molecular weights of known bacterial superantigens are more than 22,000, electrospray ionization mass spectrometry showed that the molecular weight of YPM was 14524.4. These results indicate that YPM comprises a novel superantigen with substantial structural differences from other bacterial superantigens produced by Gram-positive cocci.