Peripheral clonal deletion of superantigen-reactive T cells is enhanced by cortisone

Selective depletion of Vbeta2+CD8+ T cells in peripheral blood from rheumatic heart disease patients

Acute rheumatic fever (ARF) and its chronic valvular sequelae are the delayed consequence of a pharyngeal infection with group A Streptococcus (GAS). Several GAS proteins have been shown to be superantigens, raising the possibility that the expansion or deletion of T cells expressing specific Vbeta regions might play a role in the pathogenesis of ARF or chronic rheumatic heart disease (RHD). We therefore analyzed by four-color flow cytometry, the Vbeta repertoire on CD3, CD4 and CD8 T cells from four ARF patients, 10 RHD patients and also nine healthy controls. A selective depletion of Vbeta2+ T cells was found only in the CD8 subset of chronic RHD patients. This is of interest since a number of GAS superantigens exert their effects on Vbeta2+ cells and because only CD8+ T cells from ARF and RHD patients undergo anergy in response to GAS superantigens. Our results suggests that an ongoing immune process is present in RHD patients and that CD8+ T cells may have an important immunoregulatory role in the pathogenesis of the disease.

Tumour necrosis factor-alpha-induced apoptosis in cord blood T lymphocytes: involvement of both tumour necrosis factor receptor types 1 and 2

Cord blood T cells are much more likely to be induced to apoptosis in vitro than adult T cells. Nevertheless, the expression of Fas is markedly lower on cord blood lymphocytes than on peripheral blood lymphocytes. In the current investigation, we determined the capacity of tumour necrosis factor-alpha (TNF-alpha) to induce apoptosis in human naïve T cells in cord blood, and assessed the roles of two distinct TNF receptors (TNFRs) in mediating death signals. After activation, cord blood T cells were sensitive to TNF-alpha-induced apoptosis, and interleukin 2 (IL-2) could prevent this apoptotic response. Both TNFR1 (p55) and TNFR2 (p75) expressed on activated cord blood T cells were able to transmit apoptotic signals. Moreover, a synergistic effect was observed by a combination of TNFR1- and TNFR2-signals. Additionally, CD4(+) T cells showed higher sensitivity to TNFR-mediated apoptosis than CD8(+) T cells. These data suggest that TNF-alpha probably is a mediator of apoptosis in cord blood T cells in vivo and may contribute to the low incidence of graft-versus-host disease in cord blood transplantation.

Direct detection of apoptotic cells in peripheral blood from highly pathogenic SHIV-inoculated monkey

Apoptosis in peripheral blood leukocytes (PBL) has been estimated by the enhancement of spontaneous apoptosis after in vitro culture, because apoptotic cells have not been observed directly in freshly isolated PBL in the course of HIV/AIDS. In monkeys infected with a highly pathogenic simian/human immunodeficiency virus (SHIV), which corresponds to rapid progressors of HIV infection, a high frequency of apoptotic cells was directly detected in fresh PBL by electron-microscopic studies. Peripheral blood apoptosis transiently occurred after intense plasma viremia, and peaking at 3 weeks postinfection; occurrence was not limited specifically to lymphocytes, but also occurred in other types of leukocytes. Apoptosis in peripheral lymph nodes was also detected following intense plasma viremia. However, the in vivo apoptosis was not detected in nonpathogenic SHIV-infected monkeys that showed no cell loss. Thus, we directly showed the apoptosis of PBL, which might be associated with pathogenic SHIV produced during the time of plasma viremia.

Tumor necrosis factor receptor p55 mediates deletion of peripheral cytotoxic T lymphocytes in vivo

Cellular death of activated lymphocytes down-regulates immune responses and is involved in maintaining self tolerance. Signals associated with ligation of the membrane molecule Fas lead to lymphocyte apoptosis, but additional, Fas-independent mechanisms have been postulated. Here, we show a marked expansion and prolonged persistence of functional activated cytotoxic T cells in mice lacking the tumor necrosis factor (TNF) receptor p55. In the absence of this receptor, peripheral lymphocyte apoptosis was significantly reduced in vivo. The prolonged thymocyte survival was associated with functional anergy, since the T cells no longer proliferated in vitro when stimulated with peptide antigen. However, specific cytotoxic effector function was easily detected in vitro. We conclude that the TNF receptor p55 is involved in peripheral T cell deletion in vivo.

Addition of corticosteroids to antibiotic treatment ameliorates the course of experimental Staphylococcus aureus arthritis

OBJECTIVE

To evaluate the combined effect of systemic corticosteroid and antibiotic therapy on the course of septic arthritis.

METHODS

The murine model of hematogenously acquired Staphylococcus aureus arthritis was used. Mice were treated with corticosteroids and antibiotics, and were followed up individually. Arthritis was evaluated clinically and histopathologically. Serum samples and bacterial isolates were also analyzed.

RESULTS

The prevalence of arthritis 14 days after the onset of the disease was 22% in the corticosteroid and antibiotic-treated group, as compared with 81% in the control (nontreated) group and 48% in the antibiotic-treated group. The severity of arthritis also decreased in the corticosteroid and antibiotic-treated group, as did the mortality rate. Immunohistochemical analysis revealed a dramatic decrease in T cells and macrophages in the synovium of mice that took the combined therapy. The mechanisms leading to this outcome include the inhibitory effect of corticosteroids on T cell and B cell proliferation and differentiation, such as suppression of interferon-gamma (IFN gamma) production. Serum levels of IFN gamma were decreased 4-fold in the antibiotic-treated group compared with the controls; a 15-fold decrease was observed in the corticosteroid and antibiotic-treated animals. In addition, serum NO3- was significantly decreased in mice treated with antibiotics (P < or = 0.05), as well as in mice treated with corticosteroids and antibiotics (P < or = 0.001).

CONCLUSION

Systemic corticosteroid administration along with antibiotic therapy had beneficial effects on the course and outcome of S aureus arthritis.

Superantigens

Superantigens are potent modulators of the immune system. Some of their biological and immunological properties are reviewed here with special attention to their potential significance for cutaneous inflammation, specific skin immune responses and skin diseases.

The role of endogenous glucocorticoids on host T cell populations in the peripheral lymphoid organs of mice with graft-versus-host disease

Previously, we demonstrated that immature CD4+8+ and mature CD4+ thymocyte populations were selectively eliminated during murine graft-versus-host disease (GVHD) as a consequence of elevated levels of endogenous glucocorticoids. In this report, we investigated whether the marked reduction of CD4+8+ and CD4+ thymocyte populations would affect host CD4+ and CD8+ T cell populations in the spleens and lymph nodes (LN) of mice undergoing GVHD. GVHD was induced in (C57BL/6 x A)F1 (B6AF1) mice by injecting A strain parental lymphoid cells. Using an antibody against H2Kb antigens, labeled host B6AF1 cells were distinguished from unlabeled donor A cells. Our results demonstrated a marked deficiency of host CD4+ and CD8+ T cells in the spleens and LN of GVHD mice on day 21 after GVHD induction. The severe reduction of host T cell populations in the peripheral lymphoid organs did not appear to result from the elimination of CD4+8+ and CD4+ thymocyte populations. However, adrenalectomy before GVHD induction reversed the severe loss of both host CD4+ and CD8+ T cell populations in the LN of GVHD mice on day 21, whereas cortisone treatment of adrenalectomized (ADX) GVHD mice resulted in reduction of host LN CD4+ and CD8+ T cell populations similar to that observed in non-ADX GVHD animals on day 21. In addition, adrenalectomy markedly improved the proliferative response of LN T cells to mitogens when compared with immunosuppressed T cells from the LN of non-ADX GVHD mice. In contrast, adrenalectomy did not reverse splenic T cell immunosuppression and the marked reduction of splenic host T cell populations during GVHD. These results suggest that high levels of endogenous glucocorticoids during GVHD play a central role in mediating severe deficiency of host T cell populations and inducing severe T cell immunosuppression in the LN, but not in the spleen, of GVHD mice.

Apoptosis of mature T lymphocytes: putative role in the regulation of cellular immune responses and in the pathogenesis of HIV infection

In this chapter, some aspects of programmed cell death, or apoptosis, of T lymphocytes are discussed. It has been recognized that transformed T cells and immature T lymphocytes can be triggered to undergo apoptosis. As in other cell systems, apoptosis is characterized by cell shrinkage, nuclear condensation, and DNA fragmentation that displays the characteristic "ladder" pattern of approximately 180-200 bp fragments. More recently, however, it has become clear that apoptosis is not restricted to immature thymocytes or transformed T lymphocytes, but can also occur in mature peripheral T cells. This raises the question of whether apoptosis plays a role as a mechanism in regulating cellular immune responses, which will be discussed in the following sections. We will also address the issue of the potential role of T cell apoptosis in pathophysiology. Here, we will concentrate on the infection with human immunodeficiency virus (HIV), where apoptosis is thought to contribute to the continuous decline in CD4+ T cells.

A functionally compromised intermediate in extrathymic CD8+ T cell deletion

We have established a model system for analyzing the induction of self-tolerance among mature peripheral T cells in V beta 5 TCR Tg mice. Both CD4+V beta 5+ and CD8+ V beta 5+ cells undergo a superantigen-driven chronic deletion in the periphery of I-E mice. Prior to their disappearance, CD4+ transgene-expressing cells are activated and then rendered anergic to further stimulation through their TCRs. This scenario differs strikingly in the CD8+ cellular compartment, which is characterized by a distinct population of CD8loV beta 5lo cells localized to the blood and spleen. CD8lo cells are small, express the surface phenotype of memory cells, and rapidly incorporate BrdU in vivo. The kinetics of their appearance and disappearance in adult thymectomized mice, the rapid chasing of BrdU from labeled cells, and their in vivo cortisone sensitivity all suggest CD8lo cells are slated for deletion. Furthermore, their functional incompetence can be documented in vitro in the absence of internucleosomal DNA fragmentation. Thus, we have identified an intermediate population of T cells targeted for peripheral deletion that, although functionally compromised, has not yet undergone programmed cell death.

Interleukin-7 rescues human activated T lymphocytes from apoptosis induced by glucocorticoesteroids and regulates bcl-2 and CD25 expression

We studied the ability of several interleukins to inhibit the cellular death of IL-2-dependent human T cells deprived of IL-2 testing viability, DNA integrity, and expression of bcl-2 gene product. Our in vitro results showed that the addition of IL-7, and in a far less efficient manner IL-4, augmented the viability of IL-2-dependent T-cell clones of different origin, specificity, and phenotype. Furthermore, IL-7 reduced the percentage of apoptotic T cells inhibiting DNA fragmentation. In addition, IL-7 but not IL-4 was consistently able to suppress the cell death of IL-2-dependent T cells triggered by DEX, a synthetic GC. The suppression of T-cell death triggered by IL-7 was not affected by the addition of anti-IL-2 antibody. Interestingly, IL-7 inhibited the downregulation of bcl-2 gene product expression that appeared on TCCs after IL-2 withdrawal and also shared with IL-2 the ability to induce the upregulation of CD25 antigen on activated T lymphocytes in the presence of DEX. These experiments establish a novel role for IL-7 in regulating viability and GC-induced apoptosis on activated human T cells and suggest that the maintenance of bcl-2 levels is a general mechanism by which interleukins preserve activated T cells from undergoing apoptosis.

Intrathymic and extrathymic clonal deletion of T cells

Clonal elimination accounts for self-tolerance induction in the thymus and also affects mature T cells responding to exogenous antigens in the periphery. Recent evidence on the microenvironments, cell-cell interactions and signalling requirements for clonal deletion of immature and mature T cells is discussed.

Neonatal deletion and selective expansion of mouse T cells by exposure to rabies virus nucleocapsid superantigen

The nucleocapsid (NC) of the rabies virus behaves as an exogenous superantigen (SAg) in humans. In the present report, we analyzed whether it is also a SAg in mice by studying the effect of NC on T cell receptor (TCR) V beta expression in BALB/c mice. Repeated injection of NC in newborn BALB/c mice led to a marked reduction by two- to sixfold of V beta 6 expressing CD4+ T cells in spleen and in peripheral blood. Decrease of V beta 6-expressing CD3+ mature T cells was also observed in thymus. Single NC injection in footpad resulted in a three- to sixfold expansion of V beta 6 CD4+ T cells, but not of CD8+ T cells, in the draining lymph nodes of BALB/c mice. The intensity of the stimulation was dose dependent and was maximal 3 d after the NC injection. The clonal deletion of T cells bearing a particular V beta demonstrates that NC is a SAg in mice. T cells, especially CD4+ T cells, are an essential factor in host resistance to rabies virus and also in the pathophysiology of paralysis; thus, we postulate that a rabies virus component, which stimulates T cells, such as a SAg, may increase virus immunopathogenicity. To evaluate this hypothesis, we compared the course of rabies in adult BALB/c lacking V beta 6, 7, 8.1, and 9 T cells and in normal BALB/c. Immune-related paralysis was decreased in BALB/c missing the NC target V beta T cells. Transfer of V beta 6 but not of V beta 8.1-3 T cells into recipient mice lacking V beta 6, 7, 8.1, and 9 allowed the immune-related paralysis to evolve. Taken together, these results strongly support the hypothesis that T cells expressing rabies SAg-specific V beta 6 T cells, are involved in the genesis of the immunopathology that is characteristic of paralytic rabies.

Clonal anergy to staphylococcal enterotoxin B in vivo: selective effects on T cell subsets and lymphokines

Injection of bacterial superantigens such as staphylococcal enterotoxin B (SEB) in adult mice results in initial proliferation of SEB-responsive V beta 8+ T cells followed by induction of a state of non-responsiveness frequently referred to as clonal anergy. We show here that SEB-induced anergy involves selective changes in lymphokine production and that it affects CD4+ V beta 8+ and CD8+ V beta 8+ T cells in different fashions. Whereas both CD4+ V beta 8+ and CD8+ V beta 8+ cells from anergic mice exhibit strongly reduced proliferative capacity and interleukin(IL)-2 production upon restimulation with SEB either in vivo or in vitro the CD8+ subset from SEB-injected mice produces other lymphokines (such as interferon(IFN)-gamma) at normal or slightly increased levels in response to SEB. Changes in the levels of production of IL-2 and IFN-gamma protein correlated well with mRNA accumulation both in vivo and in vitro. Collectively these data suggest that superantigen-induced anergy involves selective changes in signal transduction and/or gene regulation in T lymphocytes.