Tolerance in T-cell clones

The danger theory of immunity revisited

The danger theory of immunity, introduced by Polly Matzinger in 1994, posits that tissue stress, damage or infection has a decisive role in determining immune responses. Since then, a growing body of evidence has supported the idea that the capacity to elicit cognate immune responses (immunogenicity) relies on the combination of antigenicity (the ability to be recognized by T cell receptors or antibodies) and adjuvanticity (additional signals arising owing to tissue damage). Here, we discuss the molecular foundations of the danger theory while focusing on immunologically relevant damage-associated molecular patterns, microorganism-associated molecular patterns, and neuroendocrine stress-associated immunomodulatory molecules, as well as on their receptors. We critically evaluate patient-relevant evidence, examining how cancer cells and pathogenic viruses suppress damage-associated molecular patterns to evade immune recognition, how intestinal dysbiosis can reduce immunostimulatory microorganism-associated molecular patterns and compromise immune responses, and which hereditary immune defects support the validity of the danger theory. Furthermore, we incorporate the danger hypothesis into a close-to-fail-safe hierarchy of immunological tolerance mechanisms that also involve the clonal deletion and inactivation of immune cells.

Differential effects of interleukin-10 on the expression of HLA class II and CD1 molecules induced by granulocyte/macrophage colony-stimulating factor/interleukin-4

Interleukin (IL)-10 down-regulates HLA class II molecules, whether constitutively expressed or up-regulated by interferon-gamma or IL-4 on monocytes but not on B lymphocytes. In this study we show that IL-10 does not inhibit HLA class II expression induced by the combination granulocyte/macrophage colony-stimulating factor and IL-4 on monocytes, although it simultaneously abrogates the expression of CD1 molecules induced by the same combination of cytokines. CD1 molecules can act as element of genetic restriction for CD4- CD8- T lymphocytes, and the suppression of CD1 expression by IL-10 abolished antigen presentation to CD1-restricted CD4- CD8- T cell receptor-positive T cells. Although HLA class II expression was not down-regulated by IL-10, the antigen specific proliferative response of CD4+ T cells was nevertheless decreased. This was not caused by down-regulation of known co-stimulatory molecules such as B7.1, B7.2 and ICAM-1. IL-10 decreased the antigen specific proliferative response further by directly influencing the T lymphocytes. Our results indicate that IL-10 exerts some of its immunoregulatory functions by differential modulation of antigen presenting molecules, induced by the same combination of cytokines.

Molecular regulation of the IL-2 gene: rheostatic control of the immune system

The delivery of costimulation and the effects of the anergic state impinge on IL-2 production via different molecular mechanisms. The strongest experimental support at this stage suggests that CD28 signaling effects mRNA stability of several lymphokine genes including IL-2. While there may also be transcriptional effects of CD28 signals in human cells, controversy surrounding relevant TCR mimics must be addressed. In the case of clonal anergy, however, transcriptional non-responsiveness is evident when anergic cells are restimulated with TCR and costimulatory signals. This repression affects predominantly AP-1 activity. So far, the nature of the repression has not been identified.

Binding of T cell receptor to major histocompatibility complex class II-peptide complexes at the single-cell level results in the induction of antigen unresponsiveness (anergy)

Using dispersion cultures performed in semi-solid medium we demonstrate here that the interaction of T cell antigen receptor molecules with Ia-peptide complexes on the same cell surface results in T cell activation, without the production of lymphokines. This recognition of antigen at the single-cell level, induced a state of anergy which was not due to a decrease of surface T cell antigen receptor/CD3 complexes. The induction of anergy by peptide could not be prevented by the addition of various co-stimulatory signals, including antibodies to CD28, or CD2, high doses of interleukin-2 or phorbol ester.

Peptide-induced proliferation and lymphokine production in human T cells in the absence of antigen-presenting cells: role of T-cell activation state and costimulatory signals

The role of T-lymphocytes as antigen-presenting cells (APCs) for other T cells was investigated. Activated rabies-virus-specific human T-cell clones were shown to present peptide to class II major histocompatibility complex (MHC)-restricted T cells of a different fine specificity, resulting in lymphokine production and cell proliferation. Furthermore, purified and activated antigen-specific T cells could produce lymphokines and proliferate as a result of the addition of antigenic peptide in the absence of APC. The functional response of T cells to peptide in the absence of APC was amplified by the addition of phorbol ester (PMA) and was inhibited with antibodies specific to class II MHC or to the CD2 molecule. Experiments performed in single-cell suspension cultures using semisolid medium prepared with 1% agar demonstrate that T-cell proliferative and lymphokine responses to peptide both in the presence and absence of APC require the interaction of T-cell antigen receptor (TCR) molecules with class II MHC-peptide complexes on different cell surfaces (cell-cell contact). On the other hand, peptide self-presentation, which occurs by the binding of TCR with class II MHC-peptide complexes on the same cell surface (at the single-cell level), resulted in T-cell activation (i.e., high expression of surface CD2, CD25, and HLA-DR molecules), without proliferation or lymphokine secretion, a pattern observed in the induction of T-cell anergy by antigen. The results are discussed in terms of the role of class II MHC molecules on activated T-lymphocytes, which enable these cells to function as "professional APC" in the development of T-cell regulatory networks.

Effects of tolerance induction on early cell cycle progression by Th1 clones

Human gamma-globulin (HGG)-specific mouse Th1 clones exposed to tolerogenic signals provided by HGG-pulsed paraformaldehyde-fixed splenocytes (HGG-FAPC) were analyzed for antigen-induced progression through the early phases of the cell cycle. Exposure of Th1 clones to HGG-FAPC in primary cultures inhibits the ability of the clones to synthesize DNA in response to HGG and normal APC in secondary cultures. The Th1 clones in these secondary cultures were found to be blocked in G1a phase as evidenced by cell cycle analysis and by reduced numbers of cells expressing high levels of IL-2R and TfR. This cell cycle blockade of Th1 cells was not observed if the secondary cultures were stimulated with IL-2-containing Con A CM instead of antigen. These data suggest that in our system the inhibition in antigen-induced cell cycle progression associated with Th1 tolerance induction occurs at the G1a/G1b phase transition.

The other view on antigen-specific T suppressor cells: hypothesis

A close analysis of clonal anergy and T suppressor systems reveals a considerable overlap between these two phenomena in experimental conditions. While evidence accumulates in favour of anergy in the maintenance of self-tolerance and in experimental manipulations, the concept of antigen-specific T cell suppression coupled with the conventionally attributed features of T suppressor cells remain as an enigma. This has lead to a widespread scepticism and controversies. Hence synthesis of a theory to explain and (better) understand antigen-specific suppression becomes an essential task in basic immunology. In the present article the phenomenon of clonal anergy is subdivided, theoretically, into three states and then analysed in the context of different experimental systems. it is suggested that partially anergic cells, termed as state 3 cells, can be the effectors of antigen-specific suppression.

Functional inactivation of Dermatophagoides spp. (house dust mite) reactive human T-cell clones

Staphylococcal enterotoxins are able both to stimulate powerful polyclonal proliferative responses and to induce non-responsiveness of T lymphocytes expressing the appropriate T-cell antigen receptor V beta gene products. T-cell clones representative of the human response to house dust mite were identified that express either V beta 3 or V beta 6 gene products. The specificity of the latter was confirmed by serology. Pre-treatment of cloned V beta 3+ T cells with the Staphylococcus aureus enterotoxins B or C1 rendered them non-responsive to immunogenic challenge with their natural ligand, while retaining responsiveness to exogenous IL-2. Similarly, exposure of the V beta 6+ dust mite reactive T cells to the staphylococcal enterotoxin of the appropriate specificity, SEE, induced specific anergy. The development of non-responsiveness was associated with changes in the T-cell phenotypes. Downregulation of the T-cell receptor, Ti-CD3, was paralleled by enhanced expression of both CD2 and the IL-2 receptor, CD25. Differential co-modulation of CD4 and Ti-CD3 suggested that for some T cells CD4 may form part of the specific antigen recognition structure. Toxicity of the staphylococcal enterotoxins may be removed by chemical modification, thus their ability functionally to inactivate subpopulations of T cells expressing antigen-specific receptors with shared characteristics may be of potential value in the regulation of allergic diseases if the diversity of the T-cell repertoire proves to be limited.

The generation and use of human T cell clones

In this review a number of uses of human T cell clones have been discussed. Before considering T cell cloning, however, it is worth bearing in mind that there are certain disadvantages to this approach to T cell immunity, not the least of which is that these cells, adapted as they are for in vitro growth, may be unrepresentative of the normal T cell, in terms of both specificity, and function. In addition, cloning is sufficiently difficult for it to be undertaken only where monoclonal populations are essential to the desired aim. Nevertheless, the range of uses discussed, and the fact that many have had a fundamental impact on our understanding of immune mechanisms, not only as mediated by T cells, but also of the intracellular mechanisms of antigen-presentation, the nature and mode of action of the cytokines, as well as the cell surface molecules and cascade of signals that orchestrate T cell activation, indicate the importance of T cell cloning. In the future, it is probable that the use of T cell clones with defined receptor usage will improve our understanding of the mechanisms underlying disease pathogenesis, and thus aid both the prevention and treatment of disease. In addition, the T cell receptor structure will, no doubt, be elucidated, leading to a further quantum leap in our understanding of T cell immune mechanisms, as well as suggesting other avenues for exploration. In all these areas there is no doubt that the methodology of T cell cloning will continue to make a fundamental contribution.

Antigen presentation by keratinocytes induces tolerance in human T cells

Antigen recognition by interleukin 2 (IL 2)-producing T lymphocytes can lead to two distinct outcomes, depending on the nature of the antigen-presenting cell. Recognition of antigen presented by specialized antigen-presenting cells leads to T cell activation; in contrast, antigen presentation by cells which lack "accessory function" can lead to a state of specific nonresponsiveness, which is characterized by a failure to produce IL 2. We have shown in this study that co-culture of an HLA-DR1/4-restricted, influenza hemagglutinin-specific T cell clone with a specific peptide presented by interferon-gamma-induced DR4-expressing keratinocytes causes tolerance induction. This effect was DR restricted, in that it required pre-incubation of the T cell clone with keratinocytes expressing an appropriate DR type (DR4Dw14). The induction of T cell tolerance was also antigen specific; no inhibition resulted from pre-incubation of the clone with an irrelevant peptide. Furthermore cell to cell contact appeared to be necessary, and the addition of supernatant from interferon-gamma-induced keratinocytes did not cause any inhibition. This phenomenon may have relevance to the immunogenicity of transplanted cultured keratinocytes and to the effects of major histocompatibility complex class II induction on non-bone marrow-derived cells. Presentation of tissue-specific autoantigens by cells such as keratinocytes may provide a mechanism of avoiding, rather than stimulating, autoimmune reactions in the context of a local inflammatory response.

Veto function in vitro and in vivo

A CTLp recognizing another cell, called veto cell, is suppressed by that veto cell. The veto cell can itself be a CTL. For the veto function, the TCR of the veto cell is not required, hence the veto function is a backward action of CTL. Since, from the point of view of the veto cell, only self-reactive CTLp are suppressed, the veto function could be a mechanism for maintaining self tolerance of CTL. The characteristics of veto function in vitro and in vivo are discussed, as well as the potential physiological relevance.

Postnatal B cell development: influence of trinitrobenzenesulfonic acid treatment during pregnancy

Prenatal treatment with a reactive hapten may be well suited for analyzing the establishment of self tolerance because the hapten binds ubiquitously to proteins and cells and persists for a long period in the developing organism. Based on this consideration, pregnant BALB/c mice were treated with 2,4,6-trinitrobenzenesulfonic acid (TNBS), searching for differences in 2,4,6-trinitrophenyl (TNP) responsiveness in their offspring as compared to litters of untreated mice. The frequency of TNP-specific T-independent B cells of litters from TNBS-treated mothers was very low at birth and remained below 10% of controls until the age of 42 days. On the contrary, in 8-day-old prenatally TNBS-treated litters, the frequency of TNP-specific T-dependent B cells was higher than in controls. Expansion of TNP-specific B cells after antigenic stimulation of control mice started at the age of 3-4 weeks and expansion rates increased with age, while in prenatally TNBS-treated mice, significant expansion rates were seen at the age of 2 weeks only. Yet, after restimulation with TNP-lipopolysaccharide or with a TNP-anti-TNP conjugate, but not after restimulation with TNP-ovalbumin, similar numbers of plaque-forming cells (PFC) were observed with spleen cells of prenatally untreated and TNBS-treated mice, the latter revealing an exceptional predominance of IgG PFC. Thus, TNP-specific B cells were not deleted, but prenatal TNBS treatment resulted in an altered composition of TNP-specific B cell subpopulations, their regulation differing qualitatively from the one observed in prenatally untreated mice.

Antigen-specific T cell unresponsiveness in cloned helper T cells mediated via the CD2 or CD3/Ti receptor pathways

We have investigated the role of the CD2 protein in the negative regulation of immune function and report that similar to antigen and anti-CD3, the monoclonal anti-CD2 antibodies (T112 and T113) can induce specific unresponsiveness. Antigen and anti-CD2 tolerogenic signals both down-regulated the phenotypic expression of CD3-Ti. In contrast CD2 surface expression was up-regulated after exposure to peptide and down-regulated after anti-T112 and T113 preincubation. However, in both instances interleukin 2 receptor surface levels were increased. These phenotypic changes could only be partly explained by variations in the levels of the transcripts encoding the CD3-Ti and CD2 molecules.

Trinitrobenzenesulphonic acid-induced unresponsiveness at the systemic level

To investigate the mechanism underlying B-cell tolerance, which is still discussed as being the consequence of (functional) clonal deletion or suppression, limiting dilution (LD) analysis of the frequencies of B cells as well as regulatory cells after tolerance induction with trinitrobenzenesulphonic acid (TNBS) was performed. It was shown that the frequency of functionally active hapten-specific B cells was decreased to less than 10% of the frequency in untreated BALB/c mice. After an immunogenic challenge, trinitrophenyl (TNP)-specific B cells of tolerized mice expanded, but did not reach the level of TNP-specific B cells in untreated mice. The expansion of TNP-specific B cells in TNBS-tolerized mice after challenge with TNP-horse red blood cells (HRBC) as observed in LD cultures was in contrast to the absence of anti-TNP plaque-forming cells (PFC) in freshly harvested spleen cells (SC) and the non-detectability of anti-TNP antibodies (AB). Hence, the functional deletion (= anergy) of B cells in vivo appears to be sustained by regulatory cells. Analysis of the regulatory compartment revealed that tolerance induction resulted in transient augmentation of TNP-specific helper T cells (TH), continuously elevated levels of suppressor T cells (TS), and a low level of contrasuppressor T cells (TCS). But, contrary to non-tolerized mice, TCS of tolerized mice were rather refractory to stimulation with TNP-HRBC. Hence, we would like to hypothesize that clonal anergy of B cells leads to inappropriate activation of TCS, whose nominal antigens are antibodies. This in turn sustains the persistence of high levels of TS, i.e. tolerance would be maintained by interruption of feedback activation of regulatory cells via effector cells/molecules.

Protein kinase C-activating phorbol esters augment expression of T cell receptor genes

Tumor-promoting phorbol esters (PE) can modulate cellular functions and cell surface determinant expression in a variety of cell types, including T lymphocytes, presumably by activating the enzyme, protein kinase C (PKC). To examine whether PKC might be involved in regulating the expression of genes encoding the antigen-specific T cell receptor (TCR), we cultured the murine thymoma line, EL4, in the presence of 12-O-tetradecanoylphorbol 13-acetate (TPA) and analyzed the expression of TCR alpha or beta-chain genes by Northern blots. TPA stimulation of an interleukin 2 (IL 2)-producing variant, EL4+, induced a 3-4-fold increase in TCR beta, but not alpha, chain mRNA. Maximal increase was obtained with 3 ng/ml TPA and 12 h of stimulation. This effect appeared related to PKC activation because other tumor-promoting PE known to be PKC activators, but not inactive PE, induced the same increase. TPA stimulation of EL4+ cells also induced de novo expression of the IL 2 gene and subsequent secretion of this lymphokine. However, the increased expression of the TCR beta-chain gene and the induction of the IL 2 gene were not linked since expression of TCR beta-chain mRNA was increased to a similar degree in EL4+ and IL 2-nonproducing EL4- sublines, and cyclosporin A selectively blocked TPA-induced IL 2-gene expression in EL4+ cells without affecting the increase in TCR beta-chain mRNA. These findings suggest that PKC activation, an event that supposedly occurs after antigen-mediated triggering of the TCR, can regulate the expression of at least some of the genes encoding this receptor.

Contact dermatitis. A review

In recent years, there has been a dramatic rise in our understanding of contact dermatitis. This paper is a review of our knowledge of the mechanisms involved in contact dermatitis and related phenomena, the investigation of these events and the emergence of significant new allergens during the last 5 years.

Local and systemic desensitization induced by repeated epicutaneous hapten application

Frequent skin exposure of guinea pigs to the contact sensitizing agents dinitrochlorobenzene or 4-ethoxymethylene-2-phenyloxazolone induced both systemic hyposensitization and local unresponsiveness within 8 weeks. Both phenomena were hapten-specific. Decreased systemic reactivity in repeatedly painted guinea pigs is probably not due to receptor blockade or the development of hapten-specific antibodies, but rather to transient sequestration of hapten-specific effector cells within lymph nodes draining the site of hapten exposure. After discontinuation of allergen exposure, effector cells return into the circulation, as indicated by a reversal of systemic hyporesponsiveness within 5 weeks. The persistence of a cellular infiltrate at the site of repeated application and the hapten-specific unresponsiveness at this site suggest that suppressor cells play a role in local unresponsiveness. Upon discontinuation of allergen exposure, local unresponsiveness rapidly dissolves (within one week). Since the circulation is still depleted of effector cells, residual hyporesponsiveness may persist for longer periods.

Rational design and application of idiotope vaccines

Current emphasis on risk factors associated with established vaccines and pressing needs for vaccines against certain viral transmitted diseases have stimulated the search for new conceptual and practical approaches to vaccine production. Among these developments, the idiotope vaccine method has produced promising results. In this review the basic and conceptual principles for idiotype vaccine design are discussed. A novel approach for identifying idiotopic structures in the three dimensional structure of internal idiotope antigens is developed. The method is based on the relationship of the immune response with the evolutionary variation and diversity of the immunoglobulin family. Idiotopic structures are found in specialized topographic regions on the surface of the immunoglobulin molecule. The knowledge of these idiotope domains will facilitate the synthesis of idiotope expressing peptides and the computer modeling of the three dimensional structure of internal idiotope antigens. Finally, the existing evidence for successful application of the idiotope vaccine method is summarized and new disease groups are identified which could benefit from the development of idiotope vaccines.