Effect of staphylococcal enterotoxin B injection on the development of experimental autoimmune encephalomyelitis: influence of cytokine and inducible nitric oxide synthase production.

Possible mechanisms involved in the protective effect of staphylococcal enterotoxin B (SEB) injection on the subsequent development of experimental autoimmune encephalomyelitis (EAE) were investigated. Only partial clonal deletion and anergy of Vbeta8 + T-lymphocytes were documented after myelin basic protein immunization in SEB injected mice. Brain permeability was not influenced. Within the brain or during in vitro rechallenge assays SEB protected mice produced significantly more IL-10, IL-4, TNF-alpha and iNOS. It is suggested that the immune deviating effect of SEB may be involved in its EAE protective effect.

Effect of treatments with cyclosporin A and anti-interferon-gamma antibodies on the mechanisms of immune tolerance in staphylococcal enterotoxin B primed mice.

The authors were interested to investigate the effect of Cyclosporin A (CsA), known to block interleukin-2 (IL-2) production, or of anti-interferon-gamma antibodies (anti-IFN-gamma Abs) in a model of T cell tolerance induced by the injection of the superantigen Staphylococcal Enterotoxin B (SEB) in BALB/c mice. After SEB immunization, tolerance was mainly achieved through deletion and anergy of SEB-reactive V beta 8+ T cells. Association of CsA treatment with SEB led to a greater decrease of the percentage of V beta 8+ CD4+ lymphocytes in the spleen and an abolition of clonal energy. In contrast, treatment of SEB primed mice with anti-IFN-gamma Abs resulted in an increased percentage of V beta 8+ CD4+ cells without affecting the induction of clonal anergy. The authors found that 1-2 h after SEB priming, splenic mRNA levels of IFN-gamma and IL-4 were decreased by either CsA and anti-IFN-gamma Abs, whereas FasL, Bcl-2, p. 53, and c-myc levels were not influenced by either treatment. However, SEB-induced IL-2 and IL-10 mRNA expression was suppressed only by CsA, whereas tumour necrosis factor-alpha (TNF-alpha) was decreased only by anti-IFN-gamma Abs. To investigate whether the effect of CsA on the tolerance mechanisms was related to suppression of IL-2, CsA was administered together with recombinant IL-2. Whereas anergy was not influenced, the decreased percentage of V beta 8+ CD4+ cells seen in CsA-treated animals in the second week after SEB injection was partially corrected by the administration of IL-2. Experiments involving bromodeoxiuridine incorporation revealed that the latter effect of IL-2 was mainly due to a correction of the defective proliferation of V beta 8+ T cells after SEB injection in CsA-treated mice. These results suggest that the effect of CsA and anti-IFN-gamma Abs on tolerance mechanisms are in part explained by their action on cytokines.

Increased mortality and impaired clonal deletion after staphylococcal enterotoxin B injection in old mice: relation to cytokines and nitric oxide production.

In the present study peripheral T cell tolerance and the occurrence of shock were evaluated in young and old mice after injection of Staphylococcal enterotoxin B (SEB). In young mice SEB immunization leads to tolerance based on deletion and anergy of SEB-reactive V beta 8+ T cells. With aging, mice developed resistance to SEB-induced deletion of V beta 8+ T cells as well as a high sensitivity to toxic shock. Compared to young mice, older mice injected with SEB showed increased serum levels of interferon-gamma (IFN-gamma), interleukin-2 (IL-2) and IL-4. These results were confirmed by reverse transcription-polymerase chain reaction (RT-PCR), as splenic mRNA levels taken 2 h after SEB injection showed higher values of IL-2, IL-4, and IFN-gamma in old mice. In contrast, mRNA levels for FasL and tumour necrosis factor-alpha (TNF-alpha) were lower. No difference in IL-10 mRNA was found. Compared to young mice, old mice showed a high, but statistically not significantly different (P = 0.20), production of nitric oxide (NO). Blocking of IFN-gamma with antibodies or reducing IFN-gamma by depletion of natural killer (NK) cells resulted, respectively, in a complete or partial protection against mortality in aged mice. Suppressing the NO production by the NO synthase inhibitor N-nitro-L-arginine methylester (L-NAME) increased the mortality in both young and old mice, and abrogated clonal deletion in the surviving young mice. In conclusion, in young mice NO production is a key factor in the protection against mortality and the development of clonal deletion after SEB injection. The higher mortality seen in older mice is mainly related to the elevated production of IFN-gamma and occurs despite a sufficient production of NO. The decreased clonal deletion of old mice may be related to their decreased expression of Fas ligand or TNF-alpha after SEB injection.

Factors involved in peripheral T cell tolerance: the extent of clonal deletion or clonal anergy depends on the age of the tolerized lymphocytes.

After injection of SEB (staphylococcus enterotoxin B), normal adult mice, or thymectomized irradiated mice (TX irr.) reconstituted with lymphocytes taken from normal adult mice became specifically tolerant of SEB. At the same time the percentage of Vbeta8 positive CD4 lymphocytes known to be responsive to SEB was almost 50% decreased, indicating that a high level of clonal deletion was realized. In contrast, mice with an exclusively old T cell compartment (old thymectomized mice, TX irr. mice reconstituted several months previously) became tolerant of SEB without deleting their Vbeta8 + CD4 + cells, indicating that clonal anergy was the major mechanism in play in the induction of tolerance. Finally, TX irr. mice reconstituted with single positive thymocytes known to become recent thymic emigrants developed tolerance for SEB together with a high level (70%) of clonal deletion. Altogether these results indicated that the mechanism involved in peripheral tolerance depended on the age of the lymphocyte: very young lymphocytes underwent mainly clonal deletion whereas long lived lymphocytes underwent predominantly clonal anergy.