Control of T-cell activation by CD4+ CD25+ suppressor T cells

Summary: Depletion of the minor (∼10%) subpopulation of CD4⁺ T cells that co-expresses CD25 (interleukin (IL)-2 receptor α-chain) by thymectomy of neonates on the third day of life or by treatment of adult CD4⁺ T cells with anti-CD25 and complement results in the development of organ-specific autoimmunity. Autoimmune disease can be prevented by reconstitution of the animals with CD4⁺ CD25⁺ cells. CD4⁺ CD25⁺-mediated protection of autoimmune gastritis does not require the suppressor cytokines IL-4, IL-10, or transforming growth factor (TGF)-β. Mice that express a transgenic T-cell receptor (TCR) derived from a thymectomized newborn that recognizes the gastric parietal cell antigen H/K ATPase all develop severe autoimmune gastritis very early in life. CD4⁺ CD25⁺ T cells are also powerful suppressors of the activation of both CD4⁺ and CD8⁺ T cells in vitro . Suppression is mediated by a cell contact-dependent, cytokine-independent T–T interaction. Activation of CD4⁺ CD25⁺ via their TCR generates suppressor effector cells that are capable of non-specifically suppressing the activation of any CD4⁺ or CD8⁺ T cell. Activation of suppressor effector function is independent of co-stimulation mediated by CD28/CTLA-4 interactions with CD80/CD86. We propose that CD4⁺ CD25⁺ T cells recognize organ-specific antigens, are recruited to sites of autoimmune damage where they are activated by their target antigen, and then physically interact with autoreactive CD4⁺ or CD8⁺ effector cells to suppress the development of autoimmune disease.     

The immunosuppressive drug thalidomide induces T helper cell type 2 (Th2) and concomitantly inhibits Th1 cytokine production in mitogen- and antigen-stimulated human peripheral blood mononuclear cell cultures.

Thalidomide is an effective immunomodulatory drug in man, but its mechanism of action remains unclear. We hypothesized that, in addition to its reported inhibitory effects on production of monocyte-derived tumour necrosis factor-alpha (TNF-alpha), thalidomide might be effective at the level of Th immunoregulation. In a comparative study with the immunosuppressant cyclosporin A, we have demonstrated a potent and specific effect of thalidomide on cytokine production relating to the distinct Th1 and Th2 subsets. It induced and enhanced the production of IL-4 and IL-5 and, at the same dose (1000 ng/ml), significantly inhibited interferon-gamma (IFN-gamma) production in phytohaemagglutinin (PHA)-stimulated human peripheral blood mononuclear cell (PBMC) cultures. Stimulation of PBMC with recall antigen (streptokinase:streptodornase (SKSD)) at 144 h in the absence of thalidomide resulted in a predominantly Th1 response, with the production of IFN-gamma and IL-2. Thalidomide switched this response from a Th1 to a Th2 type. The effect was most pronounced at 1000 ng/ml thalidomide, where inhibition of IFN-gamma and enhancement of IL-4 production was maximal. In unstimulated cultures thalidomide alone induced IL-4 production. Cyclosporin A, in contrast, inhibited both Th1 and Th2 cytokine production by PHA-stimulated PBMC. Time course data from thalidomide-treated cultures revealed that the augmented IL-4 production diminished as the culture time increased, whereas IFN-gamma production was significantly increased. This response might be due to activation-induced apoptosis of Th2 cells or the induction of Th2 cell anergy, in the continued presence of stimulating agents, with the emergence of IFN-gamma-secreting Th1 cells when Th2 antagonism declines. The effects of thalidomide and related compounds may enhance our understanding of the mechanisms of T helper cell selection, offer the possibility of controlled therapeutic switching between Th1 and Th2 responses, and may lead to a rational approach for the treatment of some T cell-mediated immunological disorders.     

Kinetics and functional implications of Th1 and Th2 cytokine production following activation of peripheral blood mononuclear cells in primary culture

The importance of cytokine production in some disease processes is now widely recognized. To investigate temporal relationships between cytokines, we stimulated peripheral blood mononuclear cells (PBMC) in vitro using the T cell mitogen phytohemagglutinin (PHA) and various antigens chosen to induce predominantly Th1 (streptokinase: streptodornase or purified protein derivative) or Th2 (Dermatophagoides pteronyssinus, bee or wasp venom: allergens in sensitive subjects) responses. Cytokine production was measured by sensitive bioassays or enzyme-linked immunosorbent assays. Of the 30 subjects studied, 10 were normal and 20 individuals were allergic to either D. pteronyssinus (n = 10) or bee venom (n = 10) (examined before specific allergen immunotherapy). We examined the temporal profiles of a panel of cytokines produced in prmary culture. In PHA-driven cultures, cytokines were found to be sequentially produced in the order interleukin (IL)-2, IL-4, IL-5, IL-3, interferon (IFN)-γ, IL-10, IL-6, IL-12 and tumor necrosis factor (TNF)-α. The response to allergen in allergic patients was predominantly Th2 in nature, with the production of IL-4, IL-5, IL-6 and IL-10, but little or no IFN-γ. IL-2, IL-3, TNF-α and IL-12 were also produced in low amounts. The response of both atopic and normal subjects to recall bacterial antigens was predominantly Th1, with high levels of IFN-γ, IL-2 and TNF-α. The relevance of the order, amount and speed of production, characteristic kinetics (production, consumption, homeostatic regulation) and the cell source of the cytokines are discussed.     

Describing traumatic responses and distress of community residents directly and indirectly exposed to an aircraft crash.

This study described the traumatic responses and the extent of psychological distress among residents who had been exposed directly or indirectly to an aircraft crash in Coventry, U.K. The direct exposure group consisted of 62 residents who were on the housing estate at the time of the accident and 20 who were not. They were interviewed on their subjective responses to the crash and then asked to fill in two distress measures: the Impact of Event Scale (IES) and the General Health Questionnaire (GHQ). The results showed a contrast between the responses of the two groups at the time of the crash. They also showed that the direct exposure group had a significantly higher score in the IES item of avoidance, the IES total, the GHQ items of somatization, social dysfunction, and the total score than the indirect exposure group had. Associations were then made between subjective responses and distress measures. Stepwise multiple regression analyses showed that for the direct exposure residents, the IES total was predicted by "whether they received professional help" and "whether they were worried about their safety after the crash." The GHQ total of the direct exposure residents was predicted by "anger about what had happened to them." For the indirect exposure residents, the IES total was predicted by "their present feelings when they heard planes flying over." There were no predictions found between responses and the GHQ total.     

HA14-1 selectively induces apoptosis in Bcl-2-overexpressing leukemia/lymphoma cells, and enhances cytarabine-induced cell death.

The Bcl-2 oncoprotein is commonly overexpressed in hematological malignancy, where it promotes the survival of neoplastic cells. Recently, a small molecule (HA14-1) was reported to bind the surface pocket of Bcl-2 that mediates antiapoptotic interactions, triggering apoptosis in a Bcl-2-transfected cell line. We investigated the activity of this compound in a panel of malignant hematopoietic cell lines. Consistent with its proposed role as a Bcl-2 inhibitor, HA14-1 was most cytotoxic in lines expressing high levels of Bcl-2. In addition, at lower concentrations (5-12.5 muM), the compound predominantly triggered apoptosis. However, at concentrations two-fold higher than this and above, increasing primary necrosis was observed, suggesting the onset of interactions supplementary to Bcl-2 inhibition. In experiments on primary cells, 25 muM HA14-1 induced extensive apoptosis in acute leukemic blasts, but also suppressed normal hematopoietic colony formation to <50% of baseline. Importantly, low-concentration HA14-1 (5 muM) was nontoxic to normal colony-forming cells, whereas it enhanced the cytotoxicity of the antileukemia drug cytarabine in Bcl-2-positive lymphoblastic leukemia cells. In conclusion, our results indicate that HA14-1 at low concentration selectively triggers apoptosis in malignant hematopoietic cells that overexpress Bcl-2. Agents of this class may have particular utility in combination with cytotoxic chemotherapy drugs.     

Effect of stride length on symptoms of exercise-induced muscle damage during a repeated bout of downhill running

The purpose of this study was to assess the effects of changes in stride length on the symptoms of exercise-induced muscle damage (EIMD) during a repeated bout of downhill running in a group of 18 men and women. Muscle tenderness, plasma creatine kinase activity (CK) and maximal voluntary isometric force were measured before and after two downhill runs, with each run separated by 5 weeks. The first downhill run was at the preferred stride frequency (PSF). Participants were then randomly allocated to one of three sex-balanced groups with equal numbers of men and women: overstride (-8% PSF), understride (+8% PSF) and normal stride frequency for the second downhill run. Stride length had no effect (P>0.05) on muscle tenderness, CK or isometric peak force. Increases in muscle tenderness (P<0.001) and CK were lower (P<0.05) following the second downhill run, although there was no difference in the pattern and extent of the strength decrement between the two runs. There were also no differences (P>0.05) in muscle tenderness, CK or the relative strength loss between the men and the women. Results suggest that the symptoms of EIMD are unaffected by gender and small alterations to the normal stride pattern during constant velocity downhill running. The observation that muscle tenderness and CK were reduced following a repeated bout of similar eccentric exercise is consistent with the phenomenon known as the 'repeated bout effect' of muscle damage.