Increased endogenous antigen presentation in the periphery enhances susceptibility to inflammation-induced gastric autoimmunity in mice.

How the immune system maintains peripheral tolerance under inflammatory conditions is poorly understood. Here we assessed the fate of gastritogenic T cells following inflammatory activation in vivo. Self-reactive T cells (A23 T cells) specific for the gastric H+ /K+ ATPase α subunit (HKα) were transferred into immunosufficient recipient mice and immunised at a site distant to the stomach with adjuvant containing the cognate HKα peptide antigen. Activation of A23 T cells by immunisation did not impact on either immune tolerance or protection from gastric autoimmunity in wild-type BALB/c mice. However, increased presentation of endogenously derived HKα epitopes by dendritic cells (DCs) in the gastric lymph node of IE-H+ /K+ ß transgenic mice (IEß) reduces A23 T-cell tolerance to gastric antigens after inflammatory activation, with subsequent development of gastritis. While HKα-specific A23 T cells from immunised wild-type mice were poorly responsive to in vitro antigen specific activation, A23 T cells from immunised IEß transgenic mice were readily re-activated, indicating loss of T-cell anergy. These findings show that DCs of gastric lymph nodes can maintain tolerance of pathogenic T cells following inflammatory stimulation and that the density of endogenous antigen presented to self-reactive T cells is critical in the balance between tolerance and autoimmunity.

Deletion and anergy of polyclonal B cells specific for ubiquitous membrane-bound self-antigen.

B cell tolerance to self-antigen is critical to preventing antibody-mediated autoimmunity. Previous work using B cell antigen receptor transgenic animals suggested that self-antigen-specific B cells are either deleted from the repertoire, enter a state of diminished function termed anergy, or are ignorant to the presence of self-antigen. These mechanisms have not been assessed in a normal polyclonal repertoire because of an inability to detect rare antigen-specific B cells. Using a novel detection and enrichment strategy to assess polyclonal self-antigen-specific B cells, we find no evidence of deletion or anergy of cells specific for antigen not bound to membrane, and tolerance to these types of antigens appears to be largely maintained by the absence of T cell help. In contrast, a combination of deleting cells expressing receptors with high affinity for antigen with anergy of the undeleted lower affinity cells maintains tolerance to ubiquitous membrane-bound self-antigens.

Regulation of T cell activation and anergy by the intensity of the Ca²+ signal in cooperation with other signals.

The results of our previous in vitro study indicated that the intensity of the Ca²+ signal could determine T cell activation and anergy. We show here that the T cell response of mice that had been treated with cyclosporine A during oral tolerance induction was higher than that of control mice, indicating that the Ca²+ signal could also determine T cell activation and tolerization in vivo. However, T cell activation was not apparent at any concentration of ionomycin, although a low dose of anti-CD3 monoclonal antibody (mAb) induced activation, while a high dose induced anergy in vitro. These results indicate that the balance between the Ca²+ signal and other signals which can also be induced by anti-CD3 stimulation, but not the actual intensity of the Ca²+ signal or the presence of co-stimulation, played an important role in regulating T cell activation and anergy.

Atorvastatin induces T cell anergy via phosphorylation of ERK1.

Modulation of T cell response is a novel property of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors. Previously we reported the benefits of atorvastatin treatment in experimental autoimmune encephalomyelitis, the murine model of the T cell-mediated autoimmune disorder multiple sclerosis, in which a blockade of the T cell cycle by atorvastatin was attributed to an accumulation of the negative regulator p27(Kip1). We show in this report that, in line with the documented role of p27(Kip1) in T cell anergy, treatment with atorvastatin results in a deficient response to a second productive stimulus in human T cells. This effect of atorvastatin was dependent on HMG-CoA reduction and required IL-10 signaling. Importantly, atorvastatin induced an early and sustained phosphorylation of ERK1, but not ERK2, which was crucial for the induction of anergy. On the basis of the therapeutic impact of HMG-CoA reductase inhibitors, the present findings should pave the way for future therapeutic concepts related to tolerance induction in neuroinflammatory disorders such as multiple sclerosis.

Role of CD4+ regulatory T cells in hyperbaric oxygen-mediated immune nonresponsiveness.

We have previously shown that hyperbaric oxygen culture (HOC [95% O(2), 5% CO(2), 25 psi]) is an effective pretransplant tissue-modification technique that results in long-term allograft survival and the induction of systemic immune tolerance in a murine model. Here we address the immune modulatory effects of HOC-treatment of human immune responses using the in vitro mixed lymphocyte reaction (MLR). Pretreatment of allogeneic stimulator cells with HOC results in abrogation of cytotoxic T lymphocyte (CTL) activity, proliferative responses, and IFN gamma production in a 7-day MLR. These responses can be restored either by the addition of IFN gamma or IL-2 on day 0, or by blocking the activity of IL-4 and IL-10. The addition of IL-2 on day 4 does not restore allospecific CTL activity. The failure of HOC-treated cells to induce allospecific CTL is not due to the induction of anergy, demonstrated by the failure to restore responses after restimulation with allogeneic cells in the presence of IL-2. Removal of CD4(+) cells prior to restimulation, results in restoration of CTL activity in MLR cultures restimulated with HOC-treated allogeneic cells. These results suggest that HOC-induced immune nonresponsiveness is mediated by the development of CD4(+) regulatory cells in a Th2-type environment.

Nutrients as modulators of anergy in acquired immune deficiency syndrome.

Malnutrition induces a spectrum of immune abnormalities including a state of anergy in the host. This state is due to a decrease in CD4 + helper cells, diminished cytotoxic cell activity and reduction in production of lymphokines required for signal transduction. Human immunodeficiency virus (HIV), the retrovirus known to cause acquired immune deficiency syndrome (AIDS), leads to a state of anergy by causing similar immunological changes. Micronutrient abnormalities, concomitant infections and genetic factors, etc., are some of the compounding co-factors which further contribute to the deterioration of the immune functions in AIDS patients. Reversal of these immune abnormalities would improve the quality of life of HIV-infected individuals.

Epitope-specific T cell tolerance to phospholipase A2 in bee venom immunotherapy and recovery by IL-2 and IL-15 in vitro.

Bee venom phospholipase A2 (PLA) is the major allergen in bee sting allergy. It displays three peptide and a glycopeptide T cell epitopes, which are recognized by both allergic and non-allergic bee venom sensitized subjects. In this study PLA- and PLA epitope-specific T cell and cytokine responses in PBMC of bee sting allergic patients were investigated before and after 2 mo of rush immunotherapy with whole bee venom. After successful immunotherapy, PLA and T cell epitope peptide-specific T cell proliferation was suppressed. In addition the PLA- and peptide-induced secretion of type 2 (IL-4, IL-5, and IL-13), as well as type 1 (IL-2 and IFN-gamma) cytokines were abolished, whereas tetanus toxoid-induced cytokine production and proliferation remained unchanged. By culturing PBMC with Ag in the presence of IL-2 or IL-15 the specifically tolerized T cell response could be restored with respect to specific proliferation and secretion of the type 1 T cell cytokines, IL-2 and IFN-gamma. In contrast, IL-4, IL-5, and IL-13 remained suppressed. Treatment of tolerized T cells with IL-4 only partially restored proliferation and induced formation of distinct type 2 cytokine pattern. In spite of the allergen-specific tolerance in T cells, in vitro produced anti-PLA IgE and IgG4 Ab and their corresponding serum levels slightly increased during immunotherapy, while the PLA-specific IgE/IgG4 ratio changed in favor of IgG4. These findings indicate that bee venom immunotherapy induces a state of peripheral tolerance in allergen-specific T cells, but not in specific B cells. The state of T cell tolerance and cytokine pattern can be in vitro modulated by the cytokines IL-2, IL-4, and IL-15, suggesting the importance of microenvironmental cytokines leading to success or failure in immunotherapy.