Selective activation of murine V beta 8.2 bearing T cells by Pseudomonas exotoxin A

Acute Hepatotoxicity of Pseudomonas aeruginosa Exotoxin A in Mice Depends on T Cells and TNF

The most potent virulence factor of Pseudomonas aeruginosa, its exotoxin A (PEA), inhibits protein synthesis, especially in the liver, and is a weak T cell mitogen. This study was performed to correlate hepatotoxic and possible immunostimulatory features of PEA in vivo. Injection of PEA to mice caused hepatocyte apoptosis, an increase in plasma transaminase activities, and the release of TNF, IFN-γ, IL-2, and IL-6 into the circulation. Most strikingly, liver damage depended on T cells. Athymic nude mice or mice depleted of T cells by anti-Thy1.2 mAb pretreatment failed to develop acute hepatic failure, and survival was significantly prolonged following T cell depletion. Neutralization of TNF or lack of TNF receptors prevented liver injury. In the liver, TNF was produced by Kupffer cells before hepatocellular death occurred. After T cell depletion, Kupffer cells failed to produce TNF. Transaminase release was significantly reduced in perforin knockout mice, and it was even elevated in lpr/lpr mice. These results demonstrate that PEA induces liver damage not only by protein synthesis inhibition but also by TNF- and perforin-dependent, Fas-independent, apoptotic signals.

Effect of Pseudomonas aeruginosa exotoxin A on CD3-induced human T-cell activation

The effect of Pseudomonas aeruginosa (PA) exotoxin A (P-ExA) on CD3-induced T-cell activation was studied on the level of T-cells (proliferation, synthesis of interleukin (IL)-2, expression of IL-2R complex, ICAM-1,2 and LFA-1 molecules), and on the level of monocytes (expression of ICAM-1,2, LFA-1 molecules, as well as FcRI and CD14 receptors). We found that: (1) P-ExA blocked T-cell proliferation and this effect was totally reversed by intact monocytes, and partially by IL-2 or TPA but not by costimulatory cytokines (IL-1alpha, IL-1beta, TNF-alpha or IL-6); (2) P-ExA transiently, in short-term cultures (48 h), inhibited synthesis of IL-2; (3) prolonged stimulation (96 h) of peripheral blood mononuclear cells (PBMC) or CD4 + T-cells with P-ExA in high or low doses (100 and 10 ng/ml, respectively), enhanced the level of IL-2 in the cultures; (4) P-ExA at low dose, combined with IL-1beta, TNF-alpha or IL-6, up-regulated synthesis of IL-2; and (5) stimulation of T-cells with anti-CD3 monoclonal antibody (mAb) and P-ExA at high dose diminished the expression of the p55 chain but not of the p75 chain of IL-2R complex and slightly affected the expression of CD3 complex, ICAM-1,2 and LFA-1 molecules. Hence, P-ExA can regulate the level of IL-2 in cultures of CD3-induced T-cells either by inhibition of IL-2 consumption (when P-ExA is applied in high dose), or by induction of IL-2 production (a costimulatory effect exerted by P-ExA in low dose in combination with monokines). Action of P-ExA on monocytes resulted in: (1) inhibition of the expression of ICAM-1,2 molecules and their ligand LFA-1 molecule; (2) low expression of FcRI receptor (a ligand for Fc part of CD3 mAb); and (3) inhibition (over 90%) of the expression of CD14 molecule. In conclusion, P-ExA-induced anergy of T-cells depends on: (a) decrease in the affinity of IL-2R complex on activated T-cells; and (b) inhibition of the accessory activities of monocytes.

Stimulation of leukaemic cells from adult T-cell leukaemia patients with bacterial superantigens

Bacterial superantigens stimulate T cells in a manner that is restricted to the Vbeta of the T-cell receptor. We examined the ability of adult T-cell leukaemia (ATL) cells to respond to these superantigens. Mononuclear cells from 10 patients were cultured with staphylococcal enterotoxin A (SEA), staphylococcal enterotoxin B (SEB) or toxic shock syndrome toxin-1 (TSST-1), and their response was determined by MTT assay and 3H-thymidine incorporation assay. Cells from six patients showed a specific response to a single superantigen. In two cases the cells responded to TSST-1 and bore Vbeta2, the known target of TSST-1. In three cases the cells responded to SEA with one bearing Vbeta9, a target of SEA, and one bearing Vbeta16. In one case the cells responded to SEB. Most of the cells which proliferated in response to superantigens were determined genetically to be leukaemic. The response to TSST-1 was inhibited by anti-Vbeta2 antibody. The responding cells showed a strongly enhancement expression of interleukin-2 receptor. These findings indicate that leukaemic cells from a proportion of ATL patients have an ability to respond to T-cell receptor-dependent superantigens. This suggests that bacterial infection in such patients may contribute to the expansion of ATL cells.

Cutaneous colonization with staphylococci influences the disease activity of Sézary syndrome: a potential role for bacterial superantigens

It has previously been shown that circulating Sézary cells respond in vitro to superantigenic staphylococcal exotoxins in a manner that is restricted by their V beta usage. This study was conducted to examine whether cutaneous colonization with Staphylococcus aureus influences the activity of the skin lesions of Sézary syndrome, and whether S. aureus isolated from patients with Sézary syndrome stimulates circulating Sézary cells in vitro. Two patients with Sézary syndrome, whose skin was colonized with S. aureus, were treated with antibacterial agents, and the relation between the severity of the skin disease and the degree of S. aureus colonization was assessed. In addition, the patients' peripheral blood mononuclear cells were cultured in the presence of mitomycin C-treated S. aureus or superantigenic staphylococcal toxins. The antibacterial treatment improved the skin disease, and eliminated S. aureus in both patients. In one patient, 98% of the peripheral blood mononuclear cells bore V alpha 2V beta 17 of the T-cell receptor, indicative of the presence of an extremely high percentage of circulating Sézary cells. The peripheral blood lymphocytes from this patient responded well in vitro to superantigenic staphylococcal enterotoxin (SE), but not to SEA or toxic shock syndrome toxin-1, or to mitomycin-treated S. aureus isolated from the same patient. Cutaneous colonization by S. aureus influences the disease activity of CTCL, possibly by activation of Sézary cells by bacterial superantigenic exoproteins.

Responses of human T cells to dominant discrete protein antigens of Escherichia coli and Pseudomonas aeruginosa

Normal human beings have circulating T lymphocytes that proliferate in response to Escherichia coli and Pseudomonas aeruginosa. We performed the present study to characterize the nature of the responding T cells and to determine whether distinct or shared conventional antigens, superantigens or polyclonal activators account for T cell proliferation. Long term antigen-specific T cell lines were generated by repeated stimulation of PBMC from four donors with soluble antigen preparations of E. coli or P. aeruginosa. This resulted in the emergence of distinct T cell populations, which responded to strains of either E. coli or P. aeruginosa, but not to both. Trypsin treatment of the bacterial preparations largely eliminated their ability to stimulate the T cells. The T cell lines were predominantly CD4+ and their proliferation to bacterial antigens was optimal using autologous APC. E. coli T cell lines proliferated not only in response to the E. coli strain with which they were initially selected, but also to four different strains of E. coli, as well as to several related Gram-negative species. P. aeruginosa selected T cells exhibited proliferative responses to six different P. aeruginosa strains, but not to the other Gram-negative species. The finding that repeated stimulation of PBMC with E. coli or P. aeruginosa leads to CD4+ T cells highly reactive with conventional protein antigens specific either for E. coli or P. aeruginosa indicates that these bacteria possess separate dominant protein antigens that drive the proliferation of peripheral blood T cells.

Accessory cell ability of Langerhans cells for superantigen is resistant to ultraviolet-B light

We examined the effects of ultraviolet-B (UVB) irradiation on the accessory cell ability of Langerhans cells (LC) to induce a T-cell response to a superantigen, staphylococcal enterotoxin B (SEB). The ability of LC-enriched epidermal cells (LC-EC) to evoke a T-cell response to SEB was retained at the doses of UVB (up to 40 mJ/cm2) that profoundly affected the antigen-presenting function of LC-EC for a hapten, trinitrophenyl (TNP), and a protein antigen, conalbumin. Thus, the LC accessory function for superantigens is more resistant to UVB irradiation than that for ordinary antigens. This UVB resistance is presumably due to no requirement of antigen processing for superantigens as chemically fixed or chloroquine-treated LC-EC still retained their ability to induce T-cell responses to SEB. Higher doses of UVB (more than 60 mJ/cm2) reduced the accessory cell ability of LC-EC for SEB up to 50% of control. The addition of monoclonal antibodies against adhesion molecules between LC and T cells to the culture resulted in a substantial suppression of the T-cell response to SEB induced by nonirradiated LC-EC, while the UVB-irradiated LC-EC-induced T-cell response was not significantly blocked with these monoclonal antibodies. This suggested that the reduction of LC ability for superantigen by high doses of UVB is at least partly due to the impairment of adhesion molecules on LC by UVB irradiation.