Unique molecular surface features of in vivo tolerized T cells

3G11 expression in CD4+ T cell-mediated autoimmunity and immune tolerance

3G11 is a sialylated carbohydrate epitope of the disialoganglioside molecule expressed on mouse CD4(+) T cells. Recent research showed that 3G11 expression is related to the modulation of T cell function, i.e., 3G11(-) T cells exhibit anergic/Treg characteristics and efficiently inhibit autoimmunity in the central nervous system. The relationship between 3G11 expression and immune tolerance is summarized in this literature review.

Expression of 3G11 epitope defines subpopulations of regulatory T cells with different suppressive potency

3G11, a sialylated carbohydrate epitope on the disialoganglioside molecule, is expressed predominantly on the surface of mouse CD4(+) T cells. Our previous studies suggested that lack of the 3G11 molecule could be a new cell surface marker for regulatory CD4(+) T cells. In the present study, we explore the relationship between 3G11(-) and CD25(+) T cells, a well-defined, naturally occurring regulatory T cell population. We found that a large proportion of CD25(+)CD4(+) T cells lack expression of 3G11 and that more 3G11(-)CD4(+) T cells express Foxp3 compared to the 3G11(+)CD4(+) population. Based on 3G11 and CD25 expression we sorted four CD4(+) T cell subpopulations and tested their phenotypes. Among four CD25/3G11-related CD4(+) T cell subpopulations, CD25(+)3G11(-) T cells expressed the highest levels of Foxp3 and IL-10 and most efficiently inhibited mitogenic and antigen-specific immune responses in vitro and clinical EAE in vivo, while CD25(-)3G11(+) T cells produced a higher level of proinflammatory cytokines and enhanced autoimmune responses. Thus, among CD4(+)CD25(+) T cells, CD25(+)3G11(-) T cells represent a more effective Treg subpopulation than CD25(+)3G11(+) T cells.

FOXP3 ensembles in T-cell regulation

Our recent studies have identified dynamic protein ensembles containing forkhead box protein 3 (FOXP3) that provide insight into the molecular complexity of suppressor T-cell activities, and it is our goal to determine how these ensembles regulate FOXP3's transcriptional activity in vivo. In this review, we summarize our current understanding of how FOXP3 expression is induced and how FOXP3 functions in vivo as a transcriptional regulator by assembling a multisubunit complex involved in histone modification as well as chromatin remodeling.

Loss of the surface antigen 3G11 characterizes a distinct population of anergic/regulatory T cells in experimental autoimmune encephalomyelitis

T cell anergy is an important mechanism in the induction of peripheral tolerance against autoimmune diseases, yet no surface marker unique to anergic T cells in these diseases has been identified. In this study we induced in vivo anergy by i.v. tolerance against experimental autoimmune encephalomyelitis in myelin basic protein TCR transgenic mice, and showed that the hyporesponsiveness of autoantigen-reactive T cells from tolerized mice was associated with a dramatic loss of 3G11, a cell surface molecule on the surface of CD4+ T cells. Purified 3G11-CD4+ T cells lost autoantigen-induced proliferation and IL-2 production, whereas 3G11+CD4+ T cells retained responsiveness. Furthermore, 3G11- T cells actively suppressed proliferation and Th1 cytokine production of 3G11+ T cells and splenocytes of nontolerized mice. Active suppression by 3G11- T cells was at least partially due to soluble immunoregulatory factors, including IL-10. The T regulatory property of 3G11- T cells was confirmed in vivo because the transfer of purified 3G11- T cells effectively suppressed clinical experimental autoimmune encephalomyelitis. We conclude that loss of the surface molecule 3G11 characterizes a distinct population of anergic/regulatory T cells. This is the first demonstration of the ability to identify and purify anergic T cells by a distinct cell surface marker in an autoimmune disease and paves the way for a better understanding of the mechanism of tolerance in autoimmune diseases.

Sialylation regulates peripheral tolerance in CD4+ T cells

Decreased binding by the 6C10 auto-antibody serves as a unique marker for CD4+ T cell unresponsiveness after the induction of T cell tolerance in Vbeta8.1 TCR transgenic mice. We further define the nature of the epitope recognized by the 6C10 antibody to be a subset of Thy-1 bearing incompletely sialylated N-linked glycans, and furthermore, we demonstrate that tolerant CD4+ T cells have an increased degree of cell-surface sialylation. To test the significance of the altered glycosylation state identified by the 6C10 auto-antibody in the tolerant CD4+ T cell population, surface sialic acid was cleaved enzymatically. Treatment of purified peripheral CD4+ T cells with Vibrio cholerae sialidase (VCS) leads to increased 6C10 binding, significantly enhances proliferation in the tolerant CD4+ population and corrects defects in phosphotyrosine signaling observed in the tolerant CD4+ T cell. Furthermore, in vivo administration of VCS enhances proliferation in both tolerant and naive CD4+ T cell subsets. These studies suggest that sialylation of glycoproteins on the surface of the CD4+ T cell contributes to the regulation of T cell responsiveness in the tolerant state.

Differences in the Kinetics, Amplitude, and Localization of ERK Activation in Anergy and Priming Revealed at the Level of Individual Primary T Cells by Laser Scanning Cytometry

One of the potential mechanisms of peripheral tolerance is the unresponsiveness of T cells to secondary antigenic stimulation as a result of the induction of anergy. It has been widely reported that antigenic unresponsiveness may be due to uncoupling of MAPK signal transduction pathways. However, such signaling defects in anergic T cell populations have been mainly identified using immortalized T cell lines or T cell clones, which do not truly represent primary Ag-specific T cells. We have therefore attempted to quantify signaling events in murine primary Ag-specific T cells on an individual cell basis, using laser-scanning cytometry. We show that there are marked differences in the amplitude and cellular localization of phosphorylated ERK p42/p44 (ERK1/2) signals when naive, primed and anergic T cells are challenged with peptide-pulsed dendritic cells. Primed T cells display more rapid kinetics of phosphorylation and activation of ERK than naive T cells, whereas anergic T cells display a reduced ability to activate ERK1/2 upon challenge. In addition, the low levels of pERK found in anergic T cells are distributed diffusely throughout the cell, whereas in primed T cells, pERK appears to be targeted to the same regions of the cell as the TCR. These data suggest that the different consequences of Ag recognition by T cells are associated with distinctive kinetics, amplitude, and localization of MAPK signaling.

Anergy and suppression as coexistent mechanisms for the maintenance of peripheral T cell tolerance

Using T cell receptor (TCR) V(beta)8.1 transgenic mice, we have developed an in vivo system for the study of peripheral T cell tolerance, in which two distinct mechanisms of peripheral tolerance are observed to act simultaneously during the maintenance phase of the nonresponsive state. These two mechanisms, anergy and suppression, have been studied using the CD4+ T cell lineage markers 6C10 and CD25, which can be employed to purify the cells involved in each form of tolerance. Findings and perspectives gained through the study of peripheral tolerance in our model, as well as relevant observations from the literature, will be reviewed.

In vivo maintenance of T-lymphocyte unresponsiveness induced by thymic medullary epithelium requires antigen presentation by radioresistant cells

The T-cell repertoire developing in the thymus is rid of autospecific cells by the process of thymic negative selection. Recognition of major histocompatibility complex (MHC)/self-peptide complexes expressed by thymic antigen-presenting cells (APC) of bone marrow origin leads to induction of apoptotic death of autospecific thymocytes. Induction of tolerance to self-antigens not presented by thymic APC is mediated by medullary thymic epithelial cells (mTEC) which express a very wide range of proteins, e.g. inducible and tissue-specific proteins. The main type of tolerance induced by mTEC is non-deletional and the issue of how it is maintained outside the thymus is therefore of crucial interest. We have previously shown that the non-T-cell receptor (TCR) -transgenic T-cell repertoire developing in conditions in which tolerance to self-MHC/peptide ligands is exclusively induced by mTEC is tolerant to syngeneic targets in vivo but lyses such targets in vitro. Here we report that this non-deletional in vivo self-tolerance is not due to active tolerance assured by known naturally occurring regulatory or immune-modulating T lymphocytes. Importantly, we show that in vivo maintenance of this therefore probably anergic state requires continued interaction of autospecific T cells with self-MHC/peptide ligands expressed by radioresistant cells while APC are incapable of maintaining the tolerant state. Therefore, maintenance of non-deletional T-lymphocyte tolerance to the wide range of self-antigens expressed by mTEC depends on continued interaction with radioresistant cells that very probably express a much more limited repertoire of antigens. Our data may therefore have important consequences for tolerance to tissue-specific and inducible self-antigens.

Self-specific MHC class II-restricted CD4-CD8- T cells that escape deletion and lack regulatory activity

In the presence of the I-Ealpha protein, transgenic (Tg) mice expressing the 1H3.1 alphabeta TCR that is specific for the Ealpha52-68:I-A(b) complex display drastic intrathymic deletion. Although peripheral T cells from these mice remained unresponsive to the Ealpha52-68:I-A(b) complex, they contained a subpopulation able to specifically react to this complex in the presence of exogenous IL-2, indicating that some 1H3.1 alphabeta TCR Tg T cells have escaped clonal deletion and efficiently populated the periphery. IL-2-dependent, Ealpha52-68:I-A(b) complex-responsive T cells were CD4-CD8- and expressed the 1H3.1 alphabeta TCR. Such T cells could develop intrathymically, did not show sign of regulatory/suppressor activity, displayed a typical naive phenotype, and seemed to persist in vivo over time. CD4-CD8- TCR Tg T cells were also detected when the surface density of the deleting ligand was increased on MHC class II+ cells. In addition, the development of CD4-CD8- 1H3.1 alphabeta TCR Tg T cells could be supported by I-A(b) molecules. These observations indicate that CD4 surface expression neither specifies, nor is required for, the thymic export of mature thymocytes expressing a MHC class II-restricted alphabeta TCR. The data also show that, although the avidity of the interaction involved in intrathymic deletion is significantly lower than that involved in mature T cell activation, its range can be large enough to be influenced by the presence or absence of coreceptors. Finally, the margin created by the absence of CD4 coreceptor was substantial because it could accommodate various amounts of the deleting ligand on thymic stromal cells.

Modulation of Kv channel expression and function by TCR and costimulatory signals during peripheral CD4(+) lymphocyte differentiation

Ionic signaling pathways, including voltage-dependent potassium (Kv) channels, are instrumental in antigen-mediated responses of peripheral T cells. However, how Kv channels cooperate with other signaling pathways involved in T cell activation and differentiation is unknown. We report that multiple Kv channels are expressed by naive CD4(+) lymphocytes, and that the current amplitude and kinetics are modulated by antigen receptor-mediated stimulation and costimulatory signals. Currents expressed in naive CD4(+) lymphocytes are consistent with Kv1.1, Kv1.2, Kv1.3, and Kv1.6. Effector CD4(+) cells generated by optimal TCR and costimulation exhibit only Kv1.3 current, but at approximately sixfold higher levels than naive cells. CD4(+) lymphocytes anergized through partial stimulation exhibit similar Kv1.1, Kv1.2, and/or Kv1.6 currents, but approximately threefold more Kv1.3 current than naive cells. To determine if Kv channels contribute to the distinct functions of naive, effector, and anergized T cells, we tested their role in immunoregulatory cytokine production. Each Kv channel is required for maximal IL-2 production by naive CD4(+) lymphocytes, whereas none appears to play a role in IL-2, IL-4, or IFN-gamma production by effector cells. Interestingly, Kv channels in anergized lymphocytes actively suppress IL-4 production, and these functions are consistent with a role in regulating the membrane potential and calcium signaling.

Differential requirements for induction of total immunoglobulin and physiological rheumatoid factor production by human peripheral blood B cells

Rheumatoid factors (RFs) are autoantibodies directed against the Fc part of IgG. Considerable evidence exists that there are two classes of RFs, pathological and physiological. Whereas pathological RFs are associated with disease, physiological RFs are considered to be a normal component of the immune response. RF(+) precursor B cells present as part of the B cell repertoire of healthy individuals are held responsible for the production of physiological RFs, which is a transient phenomenon with a clear correlation with an initiating stimulus such as immunization or exposure to an infection. Here we demonstrate a difference in the regulatory control of total Ig and RF production by peripheral blood (PB) B cells of both healthy controls (HC) and patients with rheumatoid arthritis (RA). Highly purified B cells from HC and patients with RA were cocultured with T cells stimulated with immobilized anti-CD3 mAb. Similar to IgM production, IgM-RF production was shown to be dependent on CD40 cross-linking. However, activation of PB B cells in the CD40 system in the presence of IL-2, IL-4, IL-10, combinations of these cytokines or supernatant of anti-CD3-stimulated T cells failed to induce detectable IgM-RF, whereas total IgM production was considerable. From these results we conclude that conditions to activate physiological RF(+) B cells require additional contact besides CD40--CD40L interactions between T and B cells. Since the requirements for RF production were similar using PB B cells from HC and patients with RA it is suggested that the regulatory properties of RF(+) precursors in the PB B cell compartment is equal among these groups. Together, these results indicate that conditions for the induction of total Ig and physiological RFs are different.

Suppressor T cells regulate the nonanergic cell population that remains after peripheral tolerance is induced to the Mls-1 antigen in T cell receptor Vbeta 8.1 transgenic mice

We have found suppressor T cells that inhibit the proliferative response of naive CD4(+) T cells in T cell receptor (TCR) Vbeta8.1 transgenic mice rendered tolerant in vivo by inoculation of Mls-1(a)-positive cells. This suppression was mediated by CD4(+) T cells but not by CD8(+) T cells or double-negative (DN) cells, and splenic CD4(+) T cells from tolerant mice displayed a greater suppression than lymph node CD4(+) T cells. Cell contact was required for efficient suppression, and known inhibitory cytokines such as IL-4, IL-10, and transforming growth factor beta were not involved. Suppressor T cells inhibited IL-2 production by naive CD4(+) T cells, and the addition of exogenous IL-2 diminished the suppressed activity while having little activity on tolerant T cells. Suppression was abolished by the elimination of CD25(+) T cells in the tolerant CD4(+) T cell subset. CD25(+)CD4(+) T cells suppressed the proliferative response of the residual fraction of the nonanergic population, namely, 6C10(+)CD4(+) T cells still present in the tolerant mice. However, 6C10(-)CD4(+) T cells still had reduced reactivity to Mls-1(a) even after CD25(+)CD4(+) T cells were removed and exogenous IL-2 was added. Suppressor cells appear to affect only residual nonanergic cells in situ, thereby facilitating the maintenance of the unresponsive state in vivo. These data provide a framework for understanding suppressor T cells and explain the difficulties and variables in defining their activity in other systems, because suppressor T cells apparently control only a small population of nonanergic cells in the periphery and may be viewed as a homeostatic mechanism.

Overview of vaccinology with special reference to papillomavirus vaccines

Viruses that belong to six different families are a significant cause for neoplasia in man and animals. Among them are the Papillomaviruses that cause uterine cervical cancer in women. Efforts to develop prophylactic vaccines against viruses that cause cancer are now a major research engagement. Vaccinology, the science of vaccines, engages the sciences of immunology and of microbiology, both relying heavily on molecular biology. Successful development of vaccines relies on extensive knowledge of immunology and vaccinology. Present efforts to develop vaccines against cervical cancer caused by Papillomaviruses are focused on use of the structural antigens L1 and L2 of the virus and on the oncoproteins E6 and E7. Work on Papillomavirus vaccines has been brilliantly conceived and executed and some of vaccines are now in clinical trial. Success may follow and Papillomavirus vaccine may join with the hepatitis B virus anti-cancer vaccine in the battle against cancers of man.

The suppressive effect of TGF-beta on IL-12-mediated immune modulation specific to a peptide Ac1-11 of myelin basic protein (MBP): a mechanism involved in inhibition of both IL-12 receptor beta1 and beta2

Transforming growth factor (TGF)-beta exerts a counter-regulatory effect on interleukin (IL)-12-mediated immune modulation. The underlying mechanism is not fully understood. Here we demonstrate that the expression of IL-12Rbeta1 and IL-12Rbeta2 in MBP peptide Ac1-11-primed splenocytes is upregulated upon antigen stimulation. TGF-beta induces an unresponsiveness of these primed splenocytes to IL-12 signaling through a mechanism involved in inhibition of both IL-12Rbeta1 and beta2. The modulation of IL-12Rbeta1 and beta2 expression by Ac1-11 stimulation and TGF-beta is mainly involved in CD4+ population. These data indicate that both IL-12Rbeta1 and IL-12Rbeta2 expression are crucial during T cell activation. TGF-beta-induced inhibition of IL-12R expression will reduce cellular immune responses during IL-12-mediated autoimmune disease.

Peripheral CD4+ T Cell Maturation Recognized by Increased Expression of Thy-1/CD90 Bearing the 6C10 Carbohydrate Epitope

The SM6C10 IgM autoantibody recognizes a surface determinant, 6C10, that is highly expressed on all immature thymocytes. In contrast, its expression on peripheral T cells appears developmentally regulated, i.e., absent from most naive T cells in spleen of neonatal mice, but expressed on 40–80% of naive CD4+ T cells in adult. In this paper, we demonstrate that SM6C10 recognizes a carbohydrate epitope on the Thy-1 glycoprotein using immunoprecipitation analysis, by binding to affinity-purified Thy-1 in an ELISA, and by sensitivity to N-glycosidase-F treatment. Retroviral Thy-1 gene transduction experiments into Thy-1− variant T cell lines and a pro-B cell line provide evidence that 6C10 glycosylated Thy-1 expression is not restricted to T cells but depends on the recipient cell. Therefore, differences in 6C10 levels among Thy-1+ T cells in mice likely reflect developmental regulation of posttranslational modification of the Thy-1 glycoprotein. The ability of naive CD4+ T cells to respond to anti-Thy-1 stimulation increases from neonate to adult, and 6C10− naive cells from adult mice respond poorly compared with 6C10+ cells, similar to the cells in neonatal mice. These results suggest that there is functional maturation by peripheral CD4+ T cells that coincides with 6C10 glycosylated Thy-1 up-regulation, and natural autoantibody recognizes this 6C10 carbohydrate epitope.

Dose-Dependent Induction of Distinct Anergic Phenotypes: Multiple Levels of T Cell Anergy

T cell anergy has been proposed as one of the mechanisms underlying peripheral T cell tolerance. In recent years, the functional relevance of T cell anergy has been studied extensively in vitro and in vivo, using different species, cell systems, and ways to induce anergy. Although these studies concurred about the induction of unresponsiveness, conflicting findings were obtained with respect to the function of anergic T cells and to the persistence of T cell anergy. In the present study, T cell anergy was induced through T-T presentation of the specific Ag by rat MHC class II+ T cells in the absence of professional APC. We show that, depending on the Ag dose with which T cells were incubated, distinct anergic phenotypes were induced. Incubation of T cell clones with a low (suboptimal) Ag dose induced hyporesponsiveness. Incubation with a higher (optimal) Ag dose induced an anergic state capable of exerting immunoregulatory effects. Incubation with a high (supraoptimal) Ag dose led to an anergic suppressive phenotype that was persistent and was not reversed by APC, Ag, and rIL-2. These findings demonstrate that T cell anergy is not confined to a single state of functional inactivation. Instead, multiple levels of T cell anergy exist. Thus, anergic T cells can contribute to the regulation of the immune response either in a persistent and active manner or in a passive manner, depending on their level of T cell anergy.