Bacterial superantigens induce the proliferation of resting gamma/delta receptor bearing T cells

Immunity to Staphylococcus aureus: Implications for Vaccine Development

Cell-mediated immunity seems to be critical for prevention and resolution of invasive S. aureus infections, but an imbalance in this immunity may also produce SIRS and death or an inadequate protective response with prolonged bacteremia and death. This dysregulation is likely at the heart of mortality and severe disease in humans. Anti-toxin antibodies may also come into play in reducing the severity of S. aureus infections, but these antibodies might also address superantigen-induced immune dysregulation. Thus, while changing intrinsic T cell responses may be therapeutically difficult, monoclonal antibodies against superantigens may have utility in addressing dysfunctional immune responses to S. aureus. The models above are hypotheses for examining, and potentially dramatically improving immune response to and safety of S. aureus vaccines.

Establishment of Highly Specific and Quantitative Immunoassay Systems for Staphylococcal Enterotoxin A, B, and C Using Newly-Developed Monoclonal Antibodies

Staphylococcal enterotoxin (SE) activities remain after boiling or treating with proteases. The main symptoms such as vomiting and diarrhea, are caused by the ingestion of SEs. Among SEs, SEA has been reported to be the major and most toxic protein. A highly specific and simple assay system is required to diagnose staphylococcal food poisoning. Therefore, the development of a suitable assay system is strongly anticipated. In this study, we have established a highly specific and sensitive avidin-biotin sandwich ELISA (ABS-ELISA) system for SEA, SEB, and SEC1 using newly-developed monoclonal antibodies. The linearity of these systems obtained was in the range of 0.78-25 ng/ml for each SE, and furthermore, the lower concentrations of SEs could also be detected. The recoveries of SEs from murine serum, skim milk solution, and raw milk were found to be over 90%, suggesting that our systems could detect SEs without any interventions, such as these from milk or serum proteins. We were also able to quantify SEs in 22 specimens of culture supernatants of S. aureus isolated in past occurrences. Our established system should be very useful not only in the clinical field but also in various fields of investigation because of its quantifi-cation and simplicity in detecting SEs.

γδ T cell receptor ligands and modes of antigen recognition

T lymphocytes expressing the γδ-type of T cell receptors (TCRs) for antigens contribute to all aspects of immune responses, including defenses against viruses, bacteria, parasites and tumors, allergy and autoimmunity. Multiple subsets have been individualized in humans as well as in mice and they appear to recognize in a TCR-dependent manner antigens as diverse as small non-peptidic molecules, soluble or membrane-anchored polypeptides and molecules related to MHC antigens on cell surfaces, implying diverse modes of antigen recognition. We review here the γδ TCR ligands which have been identified along the years and their characteristics, with emphasis on a few systems which have been extensively studied such as human γδ T cells responding to phosphoantigens or murine γδ T cells activated by allogeneic MHC antigens. We discuss a speculative model of antigen recognition involving simultaneous TCR recognition of MHC-like and non-MHC ligands which could fit with most available data and shares many similarities with the classical model of MHC-restricted antigen recognition for peptides or lipids by T cells subsets with αβ-type TCRs.

Superantigen recognition by gammadelta T cells: SEA recognition site for human Vgamma2 T cell receptors

Human gammadelta T cells expressing the Vgamma2Vdelta2 antigen receptors recognize nonpeptide prenyl pyrophosphate and alkylamine antigens. We find that they also recognize staphylococcal enterotoxin A superantigens in a manner distinct from the recognition of nonpeptide antigens. Using chimeric and mutant toxins, SEA amino acid residues 20-27 were shown to be required for gammadelta TCR recognition of SEA. Residues at 200-207 that are critical for specific alphabeta TCR recognition of SEA do not affect gammadelta TCR recognition. SEA residues 20-27 are located in an area contiguous with the binding site of V beta chains. This study defines a superantigen recognition site for a gammadelta T cell receptor and demonstrates the differences between Vgamma2Vdelta2+ T cell recognition of superantigens and nonpeptide antigens.

Cellular immune responses of pigs induced by vaccination with either a whole cell sonicate or pepsin-digested Brachyspira (Serpulina) hyodysenteriae bacterin

Brachyspira (Serpulina) hyodysenteriae infection of pigs (swine dysentery) causes a mucohemorrhagic diarrhea resulting in significant economic losses for producers. A commercial vaccine consisting of a proteinase-digested bacterin has shown efficacy in the reduction of disease due to B. hyodysenteriae. Vaccines consisting of whole cell bacterins, however, generally fail to protect pigs from disease. In the present study, cellular immune responses induced by a proteinase-digested bacterin were compared to responses induced by a whole cell sonicate antigen preparation. In addition, usage of either squalene or Freund's incomplete adjuvants in combination with each antigen preparation was also compared. Both antigen preparations induced significant cellular immune responses as measured by in vitro (IFN-gamma production and T cell proliferation) and in vivo methods (DTH responses). No significant differences were detected in proliferative, interferon-gamma (IFN-gamma), or delayed type hypersensitivity (DTH) responses by pigs receiving either adjuvant or antigen preparation. T cells (CD3(+)) but not B cells from vaccinated animals proliferated in response to in vitro stimulation with B. hyodysenteriae antigen. CD8(+) (single positive and CD4/CD8 double positive) and gammadelta(+) T cells were particularly responsive. In addition, high percentages of both CD8 single positive and CD4/CD8 double positive cells were detected in antigen-stimulated cultures. These findings demonstrate the unique sensitivity of porcine CD8(+) T cells to priming for recall response by vaccination with a proteinase-digested B. hyodysenteriae bacterin.

Suppression of alloreactivity with gamma delta T-cells: relevance to increased gamma delta T-cells following bone marrow transplantation

Several reports have shown that an increase in T-cell receptor gamma/delta-positive T-cells (gamma delta T-cells) have been observed following bone marrow transplantation. gamma delta T-cells expanded from peripheral blood mononuclear cells from normal volunteers were used to investigate the function of gamma delta T-cells in vitro. Peripheral blood mononuclear cells were cultured with synthetic ligand of gamma delta T-cells, monoethyl phosphates (MEP), for 7 days. MEP specifically expanded gamma delta T-cells. Expanded gamma delta T-cells from subject "B" were added to an A anti-B or A anti-C mixed lymphocyte culture (MLC) containing responder cells from subject "A" and irradiated stimulator cells from subjects "B" or "C". The cultures were harvested on day 6 and tested for cytotoxicity against stimulator-type Con A blasts. gamma delta T-cells from subject "B" specifically inhibit generation of allospecific cytotoxic T lymphocytes (CTL) in A anti-B MLC. The results indicate that gamma delta T-cells exhibit veto-type suppression of alloreaction. If the current experiments are also applicable in vivo, gamma delta T-cells originating from the donor after bone marrow transplantation may inhibit graft rejection by suppressing recipient anti-donor reactivity. gamma delta T-cells may be involved in the suppression of allogeneic reaction in vivo following allogeneic bone marrow transplantation.

Characterization of lymphocyte subpopulations in periapical lesions by flow cytometry

The mechanisms by which the bacterial root-canal infection leads to periapical bone destruction (cysts or granulomas) are not yet well understood. Previous works have shown elements of an active immune response in the lesions. In the present study, flow cytometry was used to improve the characterization of immune cells. Semiquantitative immunohistochemical analysis showed the presence of plasma cells, macrophages and B and T cells. The simultaneous use of several antibodies in flow cytometry allowed a more precise phenotype of the lymphocytes. The cysts displayed an abundance of B lymphocytes at the same time as a relative scarcity of CD8+ cells. CD4+ lymphocytes were the dominant lymphocyte population in most cases. A small number of gamma delta T lymphocytes and natural killer cells was found. These preliminary results show that flow cytometry may be used to characterize immune cells from inflamed tissue and opens the possibility for further functional studies.

Treatment of mice with staphylococcal enterotoxin B enhances resolution of an induced Escherichia coli urinary tract infection and stimulates production of proinflammatory cytokines

Staphylococcal enterotoxin B (SEB) is a superantigen that causes mass proliferation of murine Vbeta8+ T cells via major histocompatibility complex (MHC) class II molecules and leads to their apoptosis or anergy. SEB also stimulates other MHC class II-bearing cells to proliferate and secrete cytokines, some of which might enhance early host defenses against urinary tract infections (UTIs). We investigated the effect of SEB administration on the course of an induced Escherichia coli UTI in mice. Treatment with SEB 3 or 7 days before the infection had no effect on UTI resolution. However, when SEB was administered at the time of infection, bacterial colonization in the bladders was reduced at time points between 6 h and 3 days. This reduction was not due to a physiological effect, such as increased urinary glycosaminoglycans, or altered pH, nor was SEB bactericidal for the inoculum. Cytokine production in the spleens and bladders of SEB-treated and/or infected mice was evaluated by reverse transcription-PCR. SEB treatment resulted in increased levels of interleukin-2 (IL-2), IL-4, IL-6, and IL-10 mRNAs in the spleen and IL-1alpha, IL-6, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor alpha transcripts in the bladder. Also, liver cells from SEB-treated mice expressed IL-6 mRNA, which induces the production of acute-phase proteins. These data indicate that SEB treatment in vivo leads to enhanced UTI resolution through a mechanism that may include direct stimulation of effector cells in the bladder, the action of cytokines induced in the spleen, or cytokine-mediated induction of acute-phase proteins.

Abdominal T-cell non-Hodgkin's lymphoma of the gamma/delta type in a patient with selective immunoglobulin A deficiency

A 28-year-old man presented with selective immunoglobulin A deficiency and severe diarrhea responding to a gliadin-free diet. Biopsy samples of the small intestine showed dense T-cell infiltrations in the lamina propria and a slight increase of intraepithelial T-lymphocytes. No clonal rearrangement of the T-cell receptor c-beta chain genes was detectable by Southern blotting. Four years later, at the age of 32, the patient was hospitalized again with liver failure, abdominal lymphadenopathy, pancytopenia, and recurrent bacterial infections. Retrospective polymerase chain reaction analysis of formalin-fixed tissues of the intestinal biopsy samples obtained 4 years earlier showed monoclonal T-cell receptor gamma-chain gene rearrangement. Lymphoid cells of the peripheral blood showed an immunophenotype of CD3-positive gamma/delta T cells with a negativity for CD4 and CD8. A clonally rearranged T-cell receptor delta chain gene and a germline configuration of the c-beta chain genes was found by Southern blotting. Cytogenetics showed an abnormal karyotype with unbalanced translocations t(1;5) and t(9;13). The patient died of extensive lung infiltrations by gamma/delta T cells; autopsy showed a peripheral T-cell lymphoma of the gamma/delta type in the enlarged abdominal lymph nodes. This is the first report of an abdominal T-cell lymphoma of the gamma/delta type in a patient with selective immunoglobulin A deficiency.