Interleukin 4-producing CD4 T cells arise from different precursors depending on the conditions of antigen exposure in vivo

The precursor origin of T helper (Th) cell subsets in vivo has been difficult to study and remains poorly investigated. We have previously shown that chronic administration of soluble protein antigen induces selective development of antigen-specific CD4 Th2 cells in genetically predisposed mouse strains. To analyze the origin of effector T cells in this model, we designed a competitive polymerase chain reaction-based approach to track public BV-J rearrangement expressed by CD4 T cells specific for hen egg white lysozyme (HEL) in BALB/c mice. We show that public T cell clones are predominantly associated with type 1 or 2 effector Th cells recovered after primary immunization in complete or incomplete Freund's adjuvant, respectively. Conversely, continuous administration of soluble antigen, which induces strong memory Th2 response, is associated with a dose-dependent reduction of public clone size by a mechanism resembling clonal anergy. Thus, soluble HEL-induced Th2 cells do not express the public complementarity determining region 3 motifs characteristic of immunogenic challenge in the presence of adjuvant. These results demonstrate that there are multiple pathways of induction of Th2 responses depending on the condition of antigen exposure in vivo, i.e., clonal immune deviation versus recruitment of a different pool of precursor cells.     

Effect of factor VIII concentrate on antigen-presenting cell (APC)/T-cell interactions in vitro: relevance to inhibitor formation and tolerance induction

Inhibitor formation in patients with haemophilia receiving factor VIII (FVIII) concentrate is a common problem requiring tolerance induction therapy. Immune tolerance is dependent on defective T cell/antigen-presenting cell (APC) interactions and inhibitor antibody formation is associated with effective T-cell/B-cell interaction. We studied the expression of the cell-surface molecules involved with these interactions using multiparameter flow cytometry and a whole blood stimulation assay-phytohaemaglutinin (PHA) to activate T cells and Escherichia coli lipopolysaccharide (LPS) to activate monocytes and B cells. Up-regulation of T-cell co-stimulatory receptors CD11a, CD40 ligand (CD40L) and CTLA4 were inhibited in a dose-dependent manner by plasma-derived (pd)FVIII, but CD28 was unchanged. Up-regulation of monocyte and B-cell co-stimulatory ligands CD4O, B7-1 (CD80) and B7-2 (CD86) were also inhibited in a dose-dependent manner by pdFVIII, but LFA-3 (CD58) was unchanged. The combined inhibitory effect of prednisolone, an immunosuppressive agent used in several tolerance induction protocols, with pdFVIII on co-stimulatory molecules, was additive. There was no significant alteration in T-cell/APC adhesion or co-stimulatory molecules noted in the presence of recombinant (rh)FVIII concentrate. The inhibitory effect of pdFVIII on molecules involved in interaction between T cells and APCs may result in immune tolerance in recipients of pdFVIII concentrate. The inhibitory effect of pdFVIII on CD40/CD40L up-regulation may result in defective antibody formation. We now provide evidence that the use of pdFVIII, through interfering with APC/T-cell interactions, may be more appropriate than rhFVIII for tolerance induction.     

Recurrent superantigen exposure in vivo leads to highly suppressive CD4+CD25+ and CD4+CD25‐ T cells with anergic and suppressive genetic signatures

Staphylococcal enterotoxin B (SEB) activates T cells via non‐canonical signalling through the T cell receptor and is an established model for T cell unresponsiveness in vivo. In this study, we sought to characterize the suppressive qualities of SEB‐exposed CD4⁺ T cells and correlate this with genetic signatures of anergy and suppression. SEB‐exposed CD25⁺ and CD25^‐Vβ8⁺CD4⁺ T cells expressed forkhead box P3 (FoxP3) at levels comparable to naive CD25⁺ T regulatory cells and were enriched after exposure in vivo. Gene related to anergy in lymphocytes (GRAIL), an anergy‐related E3 ubiquitin ligase, was up‐regulated in the SEB‐exposed CD25⁺ and CD25^‐FoxP3⁺Vβ8⁺CD4⁺ T cells and FoxP3^‐CD25^‐Vβ8⁺CD4⁺ T cells, suggesting that GRAIL may be important for dominant and recessive tolerance. The SEB‐exposed FoxP3⁺GRAIL⁺ T cells were highly suppressive and non‐proliferative independent of CD25 expression level and via a glucocorticoid‐induced tumour necrosis factor R‐related protein‐independent mechanism, whereas naive T regulatory cells were non‐suppressive and partially proliferative with SEB activation in vitro. Lastly, adoptive transfer of conventional T cells revealed that induction of FoxP3⁺ regulatory cells is not operational in this model system. These data provide a novel paradigm for chronic non‐canonical T cell receptor engagement leading to highly suppressive FoxP3⁺GRAIL⁺CD4⁺ T cells.     

Induction of clonal anergy by oral administration of staphylococcal enterotoxin B

The staphylococcal enterotoxin is a major cause of food poisoning. The bacterial substance stimulates T cells expressing specific Vβ T cell receptors (TcR) and is termed “the superantigen”. We have previously demonstrated that intravenous injection of staphylococcal enterotoxin B (SEB) induces functional unresponsiveness (anergy) of reactive T cells as well as a partial deletion by activationinduced programmed cell death. In the present study, we examined the effect of oral administration of SEB in mice. Our results indicate that spleen T cells from SEB-primed mice are hyporesponsive to SEB stimulation in vitro, but the response to SEA was normal. Vβ8⁺ T cells purified from SEB-primed mice did not respond to stimulation of TcR. This SEB-specific unresponsiveness could not be reversed by exogenous interleukin-2, but was partially reversed by phorbol 12-myristate 13-acetate. Activation of mitogen-activated protein kinase during TcR-mediated stimulation was significantly inhibited in anergic T cells. Although the mechanisms of oral tolerance are not well understood, these results show that oral administration of SEB induce clonal anergy in peripheral T cells.     

Co-stimulation with 4-1BB ligand allows extended T-cell proliferation, synergizes with CD80/CD86 and can reactivate anergic T cells

Activation of T cells requires co-stimulation, in addition to signals through the antigen-receptor complex. Antigen encounter without adequate co-stimulation results in T-cell desensitization or anergy, a mechanism of peripheral tolerance and an apparent obstacle to cancer immunotherapy. One important co-stimulatory pathway involves CD28 engagement by CD80 or CD86. However, other ligand-receptor pairs can also provide co-stimulation and may have important functions modulating the immune response. Previous reports indicated that co-stimulation using 4-1BB ligand (4-1BBL) or agonistic anti-4-1BB antibodies could prolong T-cell responses, avoid activation-induced cell death and promote anti-tumour responses in mice. To further investigate the potential for cancer immunotherapy, we studied the effects of CD80/CD86 and 4-1BBL in repeated stimulation of human T cells and asked whether 4-1BBL might be capable of reversing anergy. We expressed CD80, CD86 and 4-1BBL in A549 lung carcinoma cells using adenovirus vectors and co-cultured these with human T cells stimulated with anti-CD3 antibody. Proliferation co-stimulated by CD80 or CD86 was transient; however, 4-1BBL-co-stimulated cultures continued to proliferate for up to 5 weeks, with repeated stimulation. Combined co-stimulation with CD80/CD86 and 4-1BBL also allowed continuous proliferation at a faster rate than either signal alone. Co-stimulation with 4-1BBL did not suppress expression of the inducible, inhibitory CD80/CD86R, CTLA-4. Significantly, we show that T cells that had become non-responsive to anti-CD3, either alone or together with CD80/CD86 co-stimulation, and thus were anergic, could be reactivated to proliferate when costimulated with 4-1BBL, either alone or combined with CD80/CD86.     

Ex vivo Stimulation of Lymphocytes with IL-10 Mimics Sepsis-Induced Intrinsic T-Cell Alterations

Profound T-cell alterations are observed in septic patients in association with increased risk of secondary infection and mortality. The pathophysiological mechanisms leading to such dysfunctions are not completely understood and direct and indirect mechanisms have been described.

In this study we evaluated whether ex vivo stimulation of lymphocytes with IL-10, an immunosuppressive cytokine released at the systemic level during sepsis, could mimic sepsis-induced intrinsic T-cell alterations.

We showed that recombinant human IL-10 priming of T cells altered their proliferative response to anti-CD2/CD3/CD28 antibody-coated beads and PHA stimulations, in a dose-dependent manner independently of accessory cells. This priming also significantly decreased T-cell secretion of IL-2 and IFNγ following stimulation. Furthermore, we demonstrated that IL-10 reduction of T-cell functionality was associated with increased FOXP3 expression in CD4⁺CD25⁺CD127^? regulatory T cells as observed in sepsis. Finally, we found that blocking the increased IL-10 concentration in plasma from septic shock patients increased the proliferative response of responding T cells from healthy controls.

We describe here an ex vivo model recapitulating features of sepsis-induced intrinsic T-cell alterations. This should help, in further studies, to decipher the pathophysiological mechanisms of T-cell alterations induced after septic shock.     

Dermatophagoides-induced interleukin-10 production by peripheral blood lymphocytes from patients with asthma in remission

Interleukin (IL)-10 is a cytokine that regulates inflammatory responses. We studied the role of IL-10 in the development of tolerance to Dermatophagoides farinae in asthma patients in remission, since asthma improves in most children during adolescence. The spontaneous production of IL-10 by cultured peripheral blood mononuclear cells (PBMC) was higher in patients with active asthma than in normal subjects. IL-10 production decreased when 1 microg/ml D. farinae was added to cultures, but increased again in a dose-dependent manner when higher concentrations of D. farinae were added. In patients with remission of asthma, IL-10 production was lower than in patients with active asthma. However, production of IL-10 showed a reciprocal increase in the presence of 1 microg/ml D. farinae, and decreased again at 10 and 50 microg/ml D. farinae. Such alterations were not observed in normal subjects. Cell lines established from patients asthma in remission showed higher IL-10 production when compared with that by cell lines from normal subjects or patients with active asthma when the cells were stimulated by D. farinae at 1 or 10 microg/ml. Neutralization of IL-10 led to revival of the D. farinae-specific proliferative response of PBMC from patients in remission, which was otherwise decreased. The increase of IL-10 production stimulated by D. farinae was inhibited by addition of an anti-IL-10 antibody. In contrast, antigen-induced interferon (IFN)-gamma production, which was increased by D. farinae stimulation when patients were in remission, did not increase after treatment with anti-IL-10, although spontaneous IFN-gamma production increased to the level seen after D. farinae stimulation. The reduced IL-4 production by cells from patients in remission after stimulation with D. farinae antigen, which was significantly higher in active patients, was not reversed by neutralization of IL-10. The D. farinae-induced IL-10/IL-4 production ratio, but not the IL-10/IL-5 production ratio, may be a significant indicator for evaluation of whether a patient has been in remission. In conclusion, D. farinae-specific anergy of T cells is likely to be induced by increased levels of IL-10 and IFN-gamma that are initially produced by specific T cells after exposure to relevant mite allergen in patients in remission.     

Prevention of anergy induction in cloned T cells by interleukin 12

Abstract A variety of tumors are potentially immunogenic but do not stimulate an effective antitumor immune response in vivo. Tumors may be capable of delivering antigen-specific signals to T cells, but may not deliver the costimulatory signals necessary for full activation of T cells. In this regard, we recently reported that a human melanoma cell line (sMC) expressing MHC class II, was able to induce clonal anergy in a specific, MHC-restricted CD-4+ T cell clone (sTC3). We used this system to investigate the influence of interleukin (IL)-12 on induction of this T cell unresponsiveness. The presence of 10 to 100 U IL-12 during the induction phase of anergy leads to a primary proliferative response of sTC3, which was significantly higher than that induced by IL-12 alone; however, in the absence of IL-12 no proliferation was seen during the induction of anergy. Subsequent optimal stimulation of IL-12 treated cells, but not of those cultured without IL-12, led to substantial IL-2 production and cell proliferation. This indicates that induction of the unresponsive state could be inhibited by IL-12. In addition, we have recently demonstrated that anergic T cell clones can produce high amounts of 1L-10 and that this event was correlated with their impaired ability to produce IL-2. This marked induction of IL-10 can be suppressed if IL-12 is present during initiation of unresponsiveness. However, IL-12 was not able to prime the T cell clone, sTC3, to become resistant against the anergizing stimulus, as this cytokine was only effective when present at the time of anergy induction. These findings indicate that IL-12 is very effective in preventing anergy when present at the same time as the anergizing stimulus, but is unable to prime T cells to resist anergy induction in this system.     

mTOR, metabolism, and the regulation of T-cell differentiation and function

Upon antigen recognition, naive T cells undergo rapid expansion and activation. The energy requirements for this expansion are formidable, and T-cell activation is accompanied by dramatic changes in cellular metabolism. Furthermore, the outcome of antigen engagement is guided by multiple cues derived from the immune microenvironment. Mammalian target of rapamycin (mTOR) is emerging as a central integrator of these signals playing a critical role in driving T-cell differentiation and function. Indeed, multiple metabolic programs are controlled by mTOR signaling. In this review, we discuss the role of mTOR in regulating metabolism and how these pathways intersect with the ability of mTOR to integrate cues that guide the outcome of T-cell receptor engagement.