Clonal anergy induced in mature V beta 6+ T lymphocytes on immunizing Mls-1b mice with Mls-1a expressing cells

Mechanisms in CD4 antibody-mediated transplantation tolerance: kinetics of induction, antigen dependency and role of regulatory T cells

CBA/Ca mice may be made tolerant to minor histoincompatible B10.BR skin grafts by treatment with a short course of non-depleting anti-mouse CD4 and CD8 monoclonal antibodies (mAb), during the transplantation period. We wished to determine when, in relation to antibody therapy, the T cells became tolerant. This was investigated by a series of adoptive transfer experiments in which mAb-treated cells were removed from therapeutic antibody at defined times after skin grafting, and exposed to fresh antigen in the absence of further mAb treatment. We show here that T cells do not become fully tolerant until 5 weeks after skin grafting. If antibody therapy is continued for the full 5 weeks, T cell tolerance can still be established, suggesting that antibody therapy does not prevent lymphocytes from registering the presence of antigen. Once the tolerant state is established, it is difficult to break that tolerance by lymphocyte infusions from normal donors. This "resistance" is mediated by T cells of the tolerant host. We show that the maintenance of both tolerance and "resistance" requires a continuous supply of antigen. When tolerant cells were "parked" in T cell-depleted mice, tolerance and "resistance" were eventually lost by 6 months. In contrast, "parked" cells exposed to fresh antigen at any time up to 4 months remained tolerant and "resistant" indefinitely. Finally, we wished to establish whether "resistance" was peculiar to this form of peripheral tolerance, or whether it might also be present in tolerance considered to be classically central. We observed resistance to be greater in the mAb-treated peripherally tolerant group, but noted that some of the centrally tolerant animals also exhibited a level of resistance above that of T cell-ablated controls. This suggests that a tolerance mechanism whose role is only minor in central tolerance may have a major role in antibody-mediated peripheral tolerance.

A murine model for B-lymphocyte somatic cell gene therapy

Mature primary B lymphocytes represent a potentially important cellular target for somatic cell gene therapy, which could prove advantageous for the treatment of certain metabolic and immunologic disorders. Their capacity to serve as antigen-presenting cells could be utilized for triggering and/or potentiating immune responses to tumors and viruses. Alternatively, B cells expressing an autoantigen could be manipulated to induce antigen-specific unresponsiveness for treatment of autoimmune diseases. Efficient expression of an exogenous gene product in long-lived B lymphocytes could be particularly useful for providing a corrected gene product in the bloodstream. Despite these advantages, efficient gene transfer into mature primary B cells has not been reported. One reason for this is that current protocols for retroviral vector-mediated gene transfer into lymphocytes rely on in vitro expansion and/or drug selection. This precludes the use of mature primary B cells as targets, since they cannot be readily cultured for long periods of time. In this report, we describe an efficient and rapid protocol for the introduction of exogenous genes into primary B cells without the need for drug selection. We have used retroviral vectors containing the human adenosine deaminase gene as a marker gene, since the biological activity of this enzyme is easy to measure and is readily distinguishable from that of the endogenous mouse adenosine deaminase. Upon adoptive transfer into SCID mice, infected B cells continuously expressing one to three copies of the human adenosine deaminase gene could be found in the spleens of recipient animals for at least 3 months.

In vivo tolerization of Th1 lymphocytes following a single feeding with ovalbumin: anergy in the absence of suppression

Oral tolerance is a biologically relevant pathway for inducing peripheral tolerance to foreign antigens. The mechanisms responsible for the tolerant state following feeding with antigen have been shown to involve both anergy and suppression. The demonstration of anergic T lymphocytes following oral tolerance has so far been limited in in vitro systems, and a primary objective of the present study was to provide evidence, in vivo, for the existence of a state of anergy in mice orally fed with ovalbumin (OVA). In addition, it has been shown that peripheral anergy following the intravenous administration of antigen is selectively induced in Th1 lymphocytes. Thus, a second objective of this study was to investigate whether tolerance induced by a feeding regimen known to cause anergy could be selectively limited to Th1 lymphocytes, and whether tolerance induction could be explained by antigen absorption from the gut into the circulation. Oral tolerance was induced by a single feeding with OVA, and was demonstrated by diminished antibody production in vivo, and by reduced cytokine secretion or proliferation in vitro. Anergy, as a mechanism for tolerance, was demonstrated by the ability to reverse the tolerant state after culturing tolerant cells in recombinant interleukin-2 (rIL-2). Reversal of the tolerant state in vivo was established by antibody production in irradiated mice adoptively transferred with cells cultured in the presence of rIL-2. The possibility that suppression was also an in vivo mechanism for tolerance was studied by adoptive transfer experiments. Our results show: 1) that a single dose of orally administered OVA leads to the selective tolerization of Th1 responses (diminished IgG2a, IL-2 and interferon-gamma production) with intact Th2 responses (IgG1, and IL-4), 2) that tolerance in vivo is explained by anergy in the absence of active suppression, 3) that exposure of tolerant cells to rIL-2 in vitro abrogates the anergic state both in vitro (proliferation and cytokine secretion) and in vivo (IgG2a production), and 4) that the induction of oral tolerance is inhibited by the presence of antibodies specific for the tolerizing antigen. These findings indicate that the induction of anergy via the oral route might depend on the dissemination of antigen absorbed from the gut. It is suggested that tolerance is guaranteed by the fact that this absorbed antigen is presented to Th1 lymphocytes in the absence of inflammatory and co-stimulatory molecules; these foreign antigens are thus not different from self antigens.

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 V beta 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 activation-induced 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. V beta 8+ 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.

An acutely lethal simian immunodeficiency virus stimulates expansion of V beta 7- and V beta 14-expressing T lymphocytes

SIVsmmPBj14, a variant simian immunodeficiency virus isolated from a pig-tailed macaque, stimulates the proliferation of macaque T lymphocytes in vitro and induces an acutely lethal disease in macaques characterized, in part, by lymphadenopathy and splenomegaly. To determine whether SIVsmmPBj14 exhibits superantigen-like activity, in vitro and in vivo studies of T-cell receptor V beta repertoire were undertaken using PCR-based quantitative methods. Whereas in vitro phytohemagglutinin stimulation of macaque peripheral blood lymphocytes did not cause a perturbation of T-cell receptor V beta repertoire, SIVsmmPBj14 stimulated the expansion of both CD4+ and CD8+ T-lymphocyte subpopulations expressing the V beta 7 and V beta 14 gene families. Such V beta 7 and V beta 14 expansions could be confirmed by a multiple RNase protection assay. Furthermore, the expansion of the same lymphocyte subpopulations was also detected in peripheral blood lymphocytes and lymph node cells of virus-infected macaques. These observations suggest that SIVsmmPBj14-mediated V beta expansion may contribute to the induction of an acutely lethal disease in macaques.

Exogenous superantigens acutely trigger distinct levels of peripheral T cell tolerance/immunosuppression: dose-response relationship

Ligand-specific immunosuppression requires an understanding of the parameters that control peripheral T cell tolerance. T cell receptor (TcR) transgenic mice offer a clear advantage for studying post-thymic tolerance mechanisms in vivo that are operational in a monoclonal T cell population with preselected antigen specificity. Yet it is unclear whether the rules defined in monoclonal T cells of genetically manipulated mice reflect those operative in clonally diverse peripheral T cells of normal mice. To analyze acute tolerance mechanisms in unselected peripheral T cells, we challenged normal mice with the superantigen staphylococcal enterotoxin B (SEB) and analyzed ligand-reactive V beta 8+ T cells for TcR-triggered tolerance mechanisms such as anergy, TcR down-regulation, or apoptosis. Upon challenge with graded doses of SEB (0.001-10 micrograms) V beta 8+ T cells become anergic within 6-16 h. Importantly, a dosage effect of SEB in regard to the level of anergy induced was observed. Anergy induced by low concentrations of SEB (0.001-0.1 microgram) is transient and is overcome by clonal growth, while higher concentrations of SEB (0.1-10 micrograms) cause long-lasting anergy resistant to cell cycle progression. At high SEB concentrations (1-10 mg) about 50% of the anergic V beta 8+ T cells additionally down-regulate their TcR-CD3 complex, followed by a loss of CD2, CD4, CD8 accessory molecules. In parallel, T cell phenotype-negative but genotypically V beta 8+ T cells are generated. The T cell phenotype-negative cells reacquire their V beta 8+ T cell phenotype upon culture in vitro. In vivo, a subset of V beta 8+ cells, defined by an intermediate stage of TcR down-regulation, i.e. V beta 8lowCD3+ cells, but not T cell phenotype-negative cells are selectively programmed for apoptosis, which occurs within 1 h. These data suggest that SEB triggers distinct tolerance pathways which operate in a hierarchical fashion in clonally diverse ligand-reactive T cells. Specifically, the results illustrate the power of exogenous superantigens to exploit these distinct tolerance pathways, thereby achieving distinct levels of immunosuppression.

Suppression of experimental antiphospholipid syndrome and systemic lupus erythematosus in mice by anti-CD4 monoclonal antibodies

OBJECTIVE

To investigate whether anti-CD4 antibodies can suppress experimental antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) induced by an anti-DNA monoclonal antibody (MAb).

METHODS

BALB/c mice were treated with anti-CD4 MAb either before or 2 months after induction of experimental APS and SLE. Control mice were treated with rat IgG or phosphate buffered saline. Serologic and clinical manifestations of the disease were determined.

RESULTS

Treatment of mice with anti-CD4 before or 2 months after disease induction prevented the development of experimental APS and SLE. The treated mice did not develop leukopenia or proteinuria, and had fewer episodes of fetal resorption. Similarly, the treated mice did not develop elevated erythrocyte sedimentation rate, prolonged activated partial thromboplastin time, or thrombocytopenia, and had significantly lower levels of antibodies to double-stranded DNA, histones, MIV-7, cardiolipin, and phosphatidylserine. Levels of CD4+ cells in the lymph nodes declined temporarily after the treatment and then returned to normal.

CONCLUSION

Anti-CD4 antibodies can prevent experimental APS and SLE. These results may suggest a role for anti-CD4 treatment in human autoimmune diseases.

Anchored polymerase chain reaction based analysis of the V beta repertoire in the non-obese diabetic (NOD) mouse

We have performed extensive analyses of T cell receptor V beta usage in the thymus, the spleen and the infiltrated islets of preclinical non-obese diabetic (NOD) mice. A semiquantitative anchored polymerase chain reaction (An-PCR) protocol has been developed for this purpose. The validity of the method has been first assessed by antibody staining with a panel of anti-V beta monoclonal antibodies (mAb). The results obtained by An-PCR are accurate, reproducible, and in good agreement with cell surface protein staining. A strict comparison between thymus and spleen repertoires reveals no major V beta-specific deletion except the already reported V beta 3 deletion due to Mtv-3. Certain V beta such as V beta 15, 18, 20 are found with a low frequency in the spleen, but the fact that they are also scarce in the thymus probably reflects a poor availability of these genetic elements during beta chain rearrangement rather than negative selection. Other V beta, such as V beta 2, V beta 12 and V beta 14 are significantly more abundant in the spleen than in the thymus. This finding was confirmed by mAb staining for V beta 2 and V beta 14. The expansion asymmetrically affects the CD4+ subset and can be traced back to the mature, single-positive thymocyte subset, suggesting an intrathymic positive selection event. V beta repertoires in infiltrated islets of 13- and 18-week-old, non-diabetic mice are polymorphic. Practically all the V beta found in the peripheral lymphoid tissues are present in the islets, in similar proportions. The major exception is V beta 12, one of the V beta which is subject to expansion during intrathymic differentiation and which is further augmented in the islets, both at 13 and 18 weeks. This increase probably reflects further peripheral amplification of the V beta 12-bearing subset due to encounter with the same ligand as in the thymus or with a cross-reactive motif. Finally, the nucleotide sequencing of all the V beta segments in usage in the NOD strain confirms the absence of allelic polymorphism of V beta-coding regions.

Split tolerance induced by orthotopic liver transplantation in mice

Spontaneous orthotopic liver allograft acceptance associated with microchimerism in mice induces tolerance to subsequent skin or heart transplants from the donor but not third-party animals. Despite in vivo hyporesponsiveness, in vitro MLC and CTL assays showed continuing antidonor reactivity. Cells isolated from recipients' spleens and grafted livers, when tested in MLC and CTL assays, were antidonor reactive out to 3 months to the same degree as splenocytes obtained from either naive or presensitized (with skin or heart) mice. Nevertheless, passive transfer of splenocytes or liver lymphocytes from liver tolerant mice, but not naive or sensitized donor strain mice, were able to prolong skin graft survival significantly in naive irradiated recipients. By using a strain combination in which the donor but not the recipient expressed the stimulatory endogenous super-Ag (Mlsf), it was possible to determine whether super-Ag-reactive T cells bearing V beta 5 and V beta 11 were deleted or anergic. Phenotypic analysis of cells isolated from recipients' spleens and grafted livers (up to 90 days after transplant), when compared with naive animals, showed no significant difference in V beta 5 and V beta 11 TCR expression. Additionally, when these isolated spleen cells were tested for antibody-mediated stimulation, both anti-V beta 5 and V beta 11 TCR mAb led to marked proliferation of cells obtained from naive and liver-transplanted recipients, but as expected, proliferation was very low in cells from naive donors. These results suggest that liver transplantation induces donor-specific tolerance in vivo, which may not be reflected in in vitro proliferative and cytotoxicity assays (split tolerance). Furthermore, this tolerance does not seem to be induced by clonal deletion or anergy of minor-lymphocyte-stimulating-antigen-reactive T cells in the recipients.

Multiple self epitopes on the Rhesus polypeptides stimulate immunologically ignorant human T cells in vitro

The extent of autoreactive T cell repertoire in the normal individual has previously been unclear. Here we demonstrate that T cells from healthy humans can be stimulated by multiple epitopes on a self protein to give primary proliferative responses in vitro. Synthetic 15-mer peptides, corresponding to the sequence of a human red blood cell Rhesus polypeptide, were tested for the ability to stimulate normal T cells. Multiple peptides were found to provoke responses reproducibly, and the proliferation could be blocked consistently by antibodies to HLA-DR, but not -DP or -DQ. T cells from each donor proliferated in response to different patterns of peptides, but this variation in pattern was less marked in individuals with the same HLA-DR type. The responses were comparable in kinetics to those elicited by the non-recall foreign antigen keyhole limpet hemocyanin, and the responding cells are most commonly derived from the CD45RA+ subpopulation, indicating that they had not been activated in vivo. It is considered that T cells are "immunologically ignorant" of many self peptides, presumably because they correspond to cryptic epitopes that are not normally presented in vivo.

Delayed allograft rejection by T cell receptor V beta 8.1 transgenic mice peripherally tolerized to Mls-1

One commonly studied model system for peripheral tolerance is the antigen-specific unresponsiveness of T cells from mice previously inoculated with superantigens such as Mls-1a. In this study, we used a TcR V beta 8.1 transgenic mouse model to investigate whether mice peripherally tolerized to Mls-1a exhibit delayed skin allograft rejection. We report dramatic prolongation of skin allograft survival in V beta 8.1 transgenic but not in non-transgenic mice tolerized to Mls-1a. Peripherally induced unresponsiveness to Mls-1a can, therefore, be considered true tolerance.

Self and nonself: duality of immune system

From the viewpoint of evolution, mammalian immunity has been developed to prevent invasion by foreign bodies including parasites and microorganisms and not to survey oncogenesis. The surveillance system on oncogenesis has been lost in the evolutionary process from amphibians to mammals. The essential duality between developmental antigens and tumor specific antigens is important in explaining what the target of self-defense mechanisms is. This duality between self-defense and defense against foreign bodies originated from invertebrates as shown in insects. Immunity has been developed to survey retrodifferentiation of somatic cells and to drive the developmental process in organogenesis. Under these conditions, the clonal deletion theory of immunocyte differentiation will lose its teleological meaning. Also, the hypothesis explaining self reactivity of immunity by the immune system recognizing only an 'internal image' composed of an idio-antiidio network of immunocytes and antibodies is overly pedantic.

Induction of anergy in resting human T lymphocytes by immobilized anti-CD3 antibodies

How the T cell receptor (TcR)/CD3 complex mediates not only the induction of T cell activation but also suppressive effects like T cell anergy or apoptosis is not well understood. Here we describe a series of preincubation and restimulation experiments which demonstrate that primary stimulation of resting, unseparated human T cells with mitogenic doses of immobilized anti-CD3 antibodies induces hyporesponsiveness upon restimulation of the cells. Various costimuli can prevent this type of anergy to a variable degree if present during the preincubation period, phorbol 12-myristate 13-acetate (PMA) being the most and anti-CD4 antibody the least effective. If employed together with anti-CD3 antibody during the restimulation phase of the assay, interleukin (IL)-2, IL-4 and anti-CD28 antibody break anergy almost completely. Proliferation induced by a submitogenic dose of anti-CD3 antibody supplemented by costimulatory signals (anti-CD2, anti-CD4, anti-CD28, IL-2, IL-4 or PMA) does not result in hyporesponsiveness. Taken together, these results support a modified view of the two-signal model for T cell activation according to which anergy induction in resting T cells occurs if primary proliferation is induced by high density triggering of the TcR/CD3 complex in the absence of accessory signals. We discuss possible implications of these findings for the induction of peripheral tolerance.

In vivo administration of interleukin-6 in murine allogeneic bone marrow chimeras: early and delayed enhancement of hematopoiesis accompanied with split tolerance but not with graft-versus-host disease

Interleukin-6 (IL-6) induced increased, leukocyte and platelet counts on around day 20 when it was administered into [BALB/c-->C3H/He] bone marrow chimeras from day 1 to day 12. Increased leukocyte counts and hemoglobin (Hb) levels were also observed at around day 60 and from day 41 to 80, respectively. On the other hand, hematopoietic recovery in [C3H/He-->C3H/He] bone marrow chimeras injected with IL-6 was different from that in [BALB/c-->C3H/He] bone marrow chimeras, showing no delayed and long-lasting increase in Hb levels but showing an early and transient increase in Hb levels and platelet counts. Sera from [BALB/c-->C3H/He] bone marrow chimeras injected with IL-6 showed predominant productions of IL-3 and/or IL-4. Reverse transcriptase polymerase chain reaction (RT-PCR) showed that stem cell factor (SCF) mRNA expression was increased in bone marrow or spleen cells from [BALB/c-->C3H/He] bone marrow chimeras injected with IL-6 on day 36. Furthermore, we analyzed influence of IL-6 on graft-versus-host disease (GVHD) in [BALB/c-->C3H/He] bone marrow chimeras injected with IL-6. Decreased survival days and body weights were not observed when compared with the control. Histopathological changes of the liver due to GVHD were also not obvious. However, alloreactive mixed lymphocyte reactions (MLRs) were readily detected although cytotoxic T cells were not generated. Since H-2 typing showed that donor-type chimerism was predominantly observed, it was suggested that split tolerance might be induced by IL-6 administration. Increased IL-2 levels were not detected in sera from [BALB/c-->C3H/He] bone marrow chimeras injected with IL-6 whereas IL-4 was detected in the same sera, indicating that type 2 helper T (TH2) cells appeared to be predominantly generated. These results suggest that IL-3/IL-4 and SCF appeared to synergistically support delayed effects on hematopoiesis in [BALB/c-->C3H/He] bone marrow chimeras injected with IL-6 although early effects appeared to be mediated mainly by IL-6 directly or indirectly. Furthermore, IL-6 could induce split tolerance in [BALB/c-->C3H/He] bone marrow chimeras via a preferable activation of TH2 type cells without inducing severe GVHD.

B cells are essential for murine mammary tumor virus transmission, but not for presentation of endogenous superantigens

Murine mammary tumor viruses (MMTVs) are retroviruses that encode superantigens capable of stimulating T cells via superantigen-reactive T cell receptor V beta chains. MMTVs are transmitted to the suckling offspring through milk. Here we show that B cell-deficient mice foster nursed by virus-secreting mice do not transfer infectious MMTVs to their offspring. No MMTV proviruses could be detected in the spleen and mammary tissue of these mice, and no deletion of MMTV superantigen-reactive T cells occurred. By contrast, T cell deletion and positive selection due to endogenous MMTV superantigens occurred in B cell-deficient mice. We conclude that B cells are essential for the completion of the viral life cycle in vivo, but that endogenous MMTV superantigens can be presented by cell types other than B cells.

Regulation of apoptosis in the immune system

Apoptosis in T and B lymphocytes is involved in all fundamental processes in the immune system. It is a mechanism to regulate the course of an immune response and to establish immunological memory as well as central and peripheral tolerance. Apoptosis in lymphocytes is regulated by gene products that induce or block this process. Elucidating the molecular basis for sensitivity and resistance towards induction of apoptosis is the key to the understanding of the development of the immune system, basic immune reactions and the pathogenesis of autoimmune diseases, AIDS and cancer.

Induction of interleukin 12 responsiveness is impaired in anergic T lymphocytes

The cytokine, interleukin 12 (IL-12), stimulates both natural killer cells and T cells to proliferate and to secrete interferon gamma (IFN-gamma). The T cell proliferative response to IL-12 must be induced and is evident after T cell receptor-mediated stimulation. As reported here, tolerant CD4+ T cells and clones, that are anergic for IL-2 production, are also anergic for induction of the proliferative response to IL-12. Murine T helper 1 clones tolerized in vitro, as well as anergic CD4+ T cells isolated from mice tolerized to the Mls-1a antigen (Ag) in vivo, demonstrated defective induction of proliferation to IL-12 upon restimulation with Ag. IL-12-enhanced production of IFN-gamma was observed in both control and anergic cells after Ag/antigen-presenting cell (APC) activation, although total IFN-gamma secretion by anergic cells was less than that produced by control cells, even in the presence of IL-12. These data indicate that T cell clonal anergy results in profound inhibition of proliferative responses, since the autocrine growth factor, IL-2, is not produced, and the APC-derived cytokine, IL-12, is not an effective stimulus for anergic T cell proliferation.

Absence of peripheral clonal deletion and anergy in immune responses of T cell-reconstituted athymic mice

Superantigens induce clonal deletion of reactive T cells in the thymus and clonal deletion and anergy in the periphery of euthymic mice. In this report we have assessed the ability of Staphylococcal enterotoxin B (SEB) to induce peripheral tolerance in nude mice reconstituted with normal, syngeneic T cells. Immunization of reconstituted nude mice with SEB resulted in lethal toxic shock in a large fraction of the animals. Such lethality was never observed in the normal donor mouse strain. Analysis of lymphokine production in response to SEB showed that reconstituted nude mice produced higher levels of interleukin-2 and tumor necrosis factor-alpha, but lower levels of interleukin-4, than euthymic control mice. Furthermore, SEB was unable to promote either clonal elimination or induction of anergy in the SEB-responsive peripheral T cells, despite the fact that reconstituted nude mice did produce high levels of corticosterone upon treatment with SEB. These results imply a lack of control over immune responses to superantigen in T cell-reconstituted athymic mice.

Analysis of the T-cell receptor beta-chain variable-region (V beta) repertoire in monozygotic twins discordant for human immunodeficiency virus: evidence for perturbations of specific V beta segments in CD4+ T cells of the virus-positive twins

We analyzed the T-cell receptor (TCR) V beta repertoire in human immunodeficiency virus type 1 (HIV-1)-infected individuals at different stages of disease. To circumvent the effect of HLA and other loci on the expressed TCR repertoire, we compared the TCR repertoire in nine pairs of monozygotic twins who were discordant for HIV infection. A semiquantitative polymerase chain reaction (PCR) assay and flow cytometry enabled us to show distinct differences in the V beta repertoire in the HIV-positive twin compared with the HIV-negative twin. By combining PCR and cytofluorometry, these differences were restricted to a specific set of TCR V beta segments, with members of the V beta 13 family perturbed in six out of seven cases and those of the V beta 21 family perturbed in four out of seven cases studied. Most of the other V beta families remained unchanged. Our results provide direct evidence for a skewed TCR repertoire in HIV infection.

Selective anergy of V beta 8+ T cells in human immunodeficiency virus-infected individuals

We have analyzed the V beta usage by CD4+ and CD8+ T cells from human immunodeficiency virus (HIV)-infected individuals in response to an in vitro stimulation with the superantigenic erythrogenic toxin A (ETA) of Streptococcus pyogenes. ETA amplifies specifically CD4+ and CD8+ T cells from control donors expressing the V beta 8 and the V beta 12 elements. When peripheral T cells from asymptomatic HIV-infected individuals were stimulated with ETA, there was a complete lack of activation of the V beta 8+ T cell subset, whereas the V beta 12+ T cell subset responded normally to the superantigen. This V beta-specific anergy, which was also observed in response to staphylococcal enterotoxin E (SEE), affected both CD4+ and CD8+ T cells and represented an intrinsic functional defect rather than a specific lack of response to bacterial superantigens since it was also observed after a stimulation with V beta 8 monoclonal antibodies. The V beta 8 anergic T cells did not express interleukin 2 receptors (IL-2Rs) and failed to proliferate in response to exogenous IL-2 or IL-4, suggesting that this anergy was not a reversible process, at least by the use of these cytokines. The unresponsiveness of the V beta 8 T cell subset is frequent since it was found in 56% of the patients studied, and comparison of the clinical status of responder vs. anergic patients indicated that the only known common factor between them was HIV infection. In addition, it is noteworthy that the anergy of the V beta 8 subset may be a very early phenomenon since it was found in a patient at Centers for Disease Control stage I of the disease. These data provide evidence that a dominant superantigen may be involved in the course of HIV infection and that the contribution of HIV has to be considered.

Activation of human T cells by the superantigen Staphylococcus enterotoxin B: analysis on a cellular level

Superantigens interact with and activate a sizeable fraction of T cells characterized by expression of specific V beta gene segments of their antigen receptor. The massive activation of T cells in an organism is considered responsible for clinical symptoms associated with superantigen-producing bacteria. Here we studied the in vitro activation of human T cells by the superantigen Staphylococcus Enterotoxin B on a cell by cell basis. Superantigen-reactive T cells were stained with a V beta 12-specific monoclonal antibody and analyzed in a cytofluorograph. Blast formation of SEB-reactive T cells occurs within 12 h and reaches a plateau after 24 h. Double-staining of V beta 12+ T cells with antibodies against different T cell activation or adhesion surface molecules revealed a time-dependent differential upregulation for CD2, CD11 = LFA-1, CD25, CD28, CD69, and HLA-DR. The expression of CD3, CD4 and CD5 was not influenced by the superantigen. The rapid phenotypic changes of superantigen reactive T cells in terms of marker expression and cell size could provide early tools in diagnosing diseases caused by superantigens.

The role of anergy in peripheral T cell unresponsiveness

When a T cell's encounter with specific antigen results in good signaling through the T cell antigen receptor yet does not lead to a proliferative response, the T cell enters a state of nonresponsiveness, or anergy. Anergy induction can result from a number of different situations, including antigen presentation by costimulation-deficient or "non-professional" antigen presenting cells, pharmacological blocking of T cell proliferation, or chronic stimulation of the T cell receptor by antigen. Anergy is a long-lived but temporary state characterized by a profound inability of the T cell to produce IL-2. Other effector functions may be affected to variable degrees. Anergy has been characterized most carefully under in vitro conditions, but several experimental models have demonstrated that T cells can also become anergic in vivo. This mechanism for tolerance induction may help to ensure that any mature autoreactive T cells which escape thymic deletion are unable to respond to host tissues. Furthermore, an understanding of the mechanism of anergy induction will most certainly lead to beneficial clinical applications, including improving graft acceptance and avoiding such deleterious immune responses as autoimmunity and allergy.

Gld and lpr mice: single gene mutant models for failed self tolerance

Mice homozygous for the gld or lpr mutations develop autoimmunity, and a lymphoproliferative disorder involving accumulation of huge numbers of unusual CD4-CD8-TCR alpha beta lo T cells. Here we review our past work with gld mice, and attempt to explain lymphoproliferation in terms of current models of T cell maturation and self-tolerance induction. The availability of molecular probes to the gene products of lpr and gld should shortly lead to a better understanding of the acquisition of self tolerance during T cell maturation and of autoimmunity.

Insulin dependent diabetes mellitus in the non-obese diabetic mouse: a disease mediated by T cell anergy?

The non-obese diabetic (NOD) mouse spontaneously develops autoimmune type I insulin-dependent diabetes mellitus (IDDM) with a similar immunopathological profile to the human disease. Development of the disease in both the NOD mouse and in humans is under polygenic control and influenced by many environmental factors. Diabetes results from a specific T cell-mediated destruction of pancreatic insulin-producing islet beta cells. Both CD4 and CD8 T cells as well as macrophages are required for the development of diabetes in NOD mice. An intriguing similarity between murine and human diabetes is a T cell proliferative unresponsiveness (anergy) that may be a susceptibility factor to disease onset. Defective communication between antigen-presenting cells (APC) and T cells, and/or an aberrant production or activity of inflammatory cytokines (e.g. chemokines) in the thymus and periphery (e.g. pancreas) may account for the unresponsiveness of regulatory T cells leading to a loss of immunological tolerance to beta cell autoantigens in NOD mice and in diabetic humans.

A role for antigen-presenting cells and bacterial superantigens in reversal of human T lymphocyte anergy

The induction of anergy in T lymphocytes generates T cells incapable of proliferation in response to a conventional antigenic stimulus. To investigate the induction and maintenance of anergy in human T cells, we used T cell-T cell presentation of myelin basic protein (MBP) or MBP synthetic peptides to induce anergy in vitro. Although anergic T cells responded normally to interleukin-2 (IL-2), these T cells did not produce IL-2 or IL-4 when peripheral blood mononuclear cells presented MBP or MBP peptides. Proliferation of anergic T cells was reduced by greater than 95% compared to nonanergic, control T cells. However, when autologous B cell lines were used to present MBP, anergy was partially reversed with a proliferation response about 50% of nonanergic levels. Bacterial superantigens also partially restored proliferation in anergic T cells following presentation by either B cell lines or macrophage isolated from peripheral blood mononuclear cells. Anergic, MBP-reactive T cells fully retained antigen-specific cytolytic activity against both B cell and T cell targets presenting MBP. These results suggest that T cell proliferative anergy may be reversible with both the type of antigen-presenting cell and superantigens potentially contributing to the initiation or maintenance of an autoimmune response.

In Mls-1a mice, fetal-type beta-gene rearrangements are frequent among self-anergic V beta 6 T cells

T lymphocytes generated in the fetal and neonatal period are characterized by T cell receptor (TCR) gene rearrangements that lack N region nucleotides (fetal-type TCR). Using fetal-type TCR as a lineage marker, we show that such T cells are long-lived and persist in the periphery of adult mice. Moreover, in both neonatal and adult environments, upon encounter with self-antigens, they are less likely to be deleted. Inefficient clonal deletion could be due to the intrinsic properties of the T cells generated during this period, or to yet unknown properties of the perinatal thymus. Such anergic T cells constitute a subset that can further expand in vivo in an antigen-independent fashion, leaving open the possibility for self-aggression under the appropriate triggering conditions.

Clonal anergy to staphylococcal enterotoxin B in vivo: selective effects on T cell subsets and lymphokines

Injection of bacterial superantigens such as staphylococcal enterotoxin B (SEB) in adult mice results in initial proliferation of SEB-responsive V beta 8+ T cells followed by induction of a state of non-responsiveness frequently referred to as clonal anergy. We show here that SEB-induced anergy involves selective changes in lymphokine production and that it affects CD4+ V beta 8+ and CD8+ V beta 8+ T cells in different fashions. Whereas both CD4+ V beta 8+ and CD8+ V beta 8+ cells from anergic mice exhibit strongly reduced proliferative capacity and interleukin(IL)-2 production upon restimulation with SEB either in vivo or in vitro the CD8+ subset from SEB-injected mice produces other lymphokines (such as interferon(IFN)-gamma) at normal or slightly increased levels in response to SEB. Changes in the levels of production of IL-2 and IFN-gamma protein correlated well with mRNA accumulation both in vivo and in vitro. Collectively these data suggest that superantigen-induced anergy involves selective changes in signal transduction and/or gene regulation in T lymphocytes.

Peripheral tolerance to alloantigen: strategies for the future

The mature, adult immune system is specifically designed to eliminate any foreign material that may enter the body, but not to respond to the body's own tissues and molecules. Indeed, during development, the potential of the immune system to respond to self antigens is removed, by eliminating or effectively silencing any autoreactive cells. These features are well adapted under normal circumstances, as they result in the efficient elimination of potentially harmful agents thereby protecting the body from infection and malignancy. However, in the context of transplantation, this 'normal' response is diametrically opposed to the desired clinical outcome, which is clearly the long term function and survival of the transplanted tissue. To prevent graft rejection the immune system of the transplant recipient has to be manipulated to ensure that it is incapacitated. Immunosuppressive drugs can be used for this purpose and are undoubtedly effective; indeed they have had a dramatic impact on success rates in clinical organ transplantation. However, as the mechanism of action of these chemical immunosuppressants is immunologically non-specific, any immune response the recipient may need to make after transplantation, as well as the rejection response, is suppressed. In addition, to maintain graft survival the drugs have to be taken indefinitely after transplantation and therefore their use is not only associated with immunological complications such as increased risks of infection and malignancy, but also numerous non-immunological side-effects. One way to overcome these problems would be to develop strategies for specific immunosuppression, such that only leukocytes capable of responding to the foreign histocompatibility or alloantigens expressed by the transplanted tissue would be affected. The ability to manipulate or reprogramme the adult immune system in such a way as to induce specific immunological unresponsiveness or tolerance to the alloantigens of the organ donor would offer many advantages over conventional immunosuppressive therapy. Only leukocytes reactive with donor alloantigens would be affected, thus allowing transplant recipients to respond effectively to other immunological stimuli, such as virus infections.

Endogenous retroviral superantigen presentation by B cells induces the development of type 1 CD4+ T helper lymphocytes

The endogenous retroviral superantigen, minor lymphocyte stimulating antigen (Mls 1a, encoded by Mtv-7), when presented by highly purified B cells induced the development of a highly polarized population of T helper (Th)1 cells from naive peripheral CD4+ T cells in vitro. Immobilized anti-V beta 6 antibodies similarly generated highly polarized, largely V beta 6+, Th 1 populations in vitro. In the presence of exogenous interleukin-4, both stimuli were capable of generating Th 2, rather than Th 1 populations. Mls 1a presentation by B cells in vivo led to the development of an equally polarized Th 1 population. Using monoclonal antibodies against interferon-gamma and transforming growth factor-beta, it was demonstrated that maximal Th 1 development with either stimulus in vitro was dependent on the endogenous production of these two cytokines. Thus, our results demonstrate that the retroviral encoded superantigen, Mls 1a, drives the development of Th 1 cells both in vitro and in vivo, and they suggest that B cell presentation does not, in itself, lead to the generation of Th 2 cells.

MHC restriction of T-cell proliferative responses in Xenopus

The MHC restriction of Xenopus allogeneic MHC- and antigen-specific T-cell proliferative responses was assessed. Xenopus MHC-specific monoclonal antibodies that recognize class I and class II molecules were tested for inhibitory effects on the generation of secondary T-cell proliferative responses. Antigen-specific T-cell lines were inhibited by anti-class II but not anti-class I monoclonal antibodies. Secondary alloantigen-specific proliferative responses also demonstrated MHC class II restriction. Allogeneic MHC- and antigen-specific T-cell lines demonstrated differential sensitivity to anti-class II monoclonal antibodies directed at discrete class II epitopes. These results indicate that Xenopus T cells interact with antigen-presenting cells similarly to mammals, and directly confirm previous data indicating that MHC class II restriction of proliferative responses is present in amphibians.

T cell immunity after a viral infection versus T cell tolerance induced by soluble viral peptides

The fate of in vivo activated CD8+ cytotoxic T cells was studied in transgenic mice expressing a T cell receptor (TCR) specific for the lymphocytic choriomeningitis virus (LCMV) glycoprotein peptide 33-41 presented by major histocompatibility complex (MHC) class I molecules. LCMV infection of TCR transgenic mice induced LCMV-specific effector and memory T cells whereas injection of soluble LCMV glycoprotein peptide 33-41 resulted in tolerance by peripheral deletion and anergy of LCMV-specific T cells after an initial expansion phase. Similarly, LCMV peptide 33-41-specific tolerance could be achieved in normal C57BL/6 mice and was not abrogated by an LCMV infection. These results obtained with a classically MHC-restricted peptide antigen parallel previous findings with retroviral or bacterial superantigens and indicate a possibility to modulate specifically mature peripheral cytotoxic T lymphocytes in vivo.

The clinical outcome of autoimmune thrombocytopenic purpura patients is related to their T cell immunodeficiency

In this work we have furthered the understanding of the alterations of T lymphocytes from 29 patients with active autoimmune thrombocytopenic purpura (ATP) and the clinical significance of their lymphocytes. An increased percentage of in vivo activated (CD25+ and DR+) T lymphocytes was found in ATP patients with respect to that found in 22 healthy controls. The function of these T cells measured as the proliferative response to polyclonal mitogenic signals is heterogeneously impaired in ATP patients. T lymphocytes from 65.5% (19/29) of the ATP patients showed a decreased proliferative response to these mitogenic signals. This functional alteration is associated with a redistribution of the T cell compartment in these patients' peripheral blood since a significant decrease of CD4+ T lymphocytes was found. We have also found that the impairment of the T cell function is different in the diverse clinical situations of the disease. Those with stable, untreated disease showed a marked decrease in the T cell proliferative response to mitogens. Furthermore, those patients who did not respond either to steroids or to splenectomy showed significantly reduced T lymphocyte blastogenesis after phytohaemagglutinin (PHA) stimulation in comparison to that found in responding patients.

Autoimmune recognition of cartilage collagens

Recent advances in basic research on the immune system and molecular biology of cartilage components have greatly increased our understanding of the role of autoimmunity in inflammatory diseases affecting joints, particularly rheumatoid arthritis. Many of these diseases are common and their complex pathogenesis probably involves a large number of genes polymorphic in the population as well as environmental factors. Characteristic features of inflammatory arthritis include expansion of the synovial tissue into a pannus containing lymphocytes and macrophages, autoimmune reactions against cartilage antigens, and erosion of cartilage. Since hyaline cartilage of the articular surfaces is the only structure within the joint known to contain joint-specific antigens this tissue is the prime suspect as the target of the autoimmune This review will first present the capacity of the immune system to discriminate between self and non-self structures, and then summarize our current understanding of the structures of cartilage collagens. Subsequently we will discuss how the immune system normally interacts with cartilage and how such interactions can lead to arthritis. We propose that collagen-induced arthritis (CIA) is valuable for understanding the autoimmune recognition of cartilage collagen which precedes the outbreak of arthritis and may perpetuate its chronicity, and serves as an animal model of rheumatoid arthritis.

Cytokines and peripheral tolerance to alloantigen

The induction of peripheral tolerance to alloantigen is accompanied in many cases by a decrease in the production of cytokines such as IL-2 and IFN gamma, yet a sustained production of cytokines such as IL-10 and IL-4. Whether or not this altered pattern of cytokine production in tolerant animals is causally related to the induction and/or maintenance of the tolerant state has yet to be fully determined, although experiments blocking selectively the action of IL-2 with CD25 antibodies suggest that manipulation of cytokine production may at least be a route to tolerance. Alternative methods for directly influencing the cytokine balance are sought and recent experiments on the CD28/CTLA-4-B7 interaction suggest a possible approach.

T cell repertoire and autoimmune diseases

Self-reactivity and autoimmunity are processes related to the breakage of self-tolerance that can be distinguished by their different clinical outcome and are widely accepted cornerstones of immunology. The finding that several potentially autoaggressive cells contribute to the repertoire of healthy individuals has stimulated a great deal of experimental work aimed at understanding the mechanisms that prevent autoimmune pathology. In this review we will consider the basic principles, and our present knowledge of the rules that preside over the interplay of the immune system with self-components. One viewpoint stresses the importance of major histocompatibility complex (MHC) and non-MHC genes in determining genetic predisposition to develop autoimmune phenomena. At a different level there is a strong interest in understanding the mechanisms of processing and presentation of self antigens, especially during ontogeny. Another topic of major interest concerns the interaction between MHC genes and the T cell receptor (TcR) complex as well as the identification of TcR V genes that are preferentially expressed by autoimmune T cells. All of these aspects are evaluated in the context of tolerance based on deletion and anergy. Finally we will propose a general model of autoimmunity based on the most recent findings concerning the biological activity of exogenous superantigens.

Self-nonself discrimination and tolerance in T and B lymphocytes

The immune system must not only fight off infections, but also ensure that it does not react against its own body tissues. Since clones of lymphocytes have predetermined reactivities, some will be self-reactive and have the potential to cause damage. They should therefore be neutralized in some way. In a system as complex and important as that governing self-tolerance, many mechanisms must exist to neutralize autoaggressive lymphocytes. They may be classified under two main groups. In one the tolerant state arises from the physical or functional silencing of potentially autoaggressive lymphocytes after antigen encounter. This may involve clonal deletion, clonal abortion or clonal anergy. In the second, regulatory mechanisms of the immune system itself may hold autoreactive lymphocytes in check, for example through the operation of idiotypic network interactions and the action of specialized suppressor cells. Much evidence has accumulated for the physical deletion of autoreactive T cells as they mature in the thymus. The fate of any that escape thymus censorship has been the subject of recent research and is discussed here. Under certain conditions, self-tolerance must also be imposed at the B-cell level to prevent the production of potentially damaging autoantibodies. Although the mechanisms which silence self-reactive lymphocytes are very efficient, self-tolerance can break down, and autoimmunity will thus ensue. The main factors responsible for this are briefly described here.

Identifying strategies for immune intervention

In recent years the molecular basis of antigen recognition by T cells has been unraveled and the various pathways that control T cell activation and functional specialization have been defined. Consequently, it is now possible to delineate various strategies for intervention with the immune system to design protective vaccines, to induce an effective response to tumor antigens, and to control graft rejection and autoimmune diseases.

Induction of foetal lethality in AKR offspring after repeated inoculations into AKR females of anti-TCR/V beta 6 monoclonal antibody

Female AKR (H-2k, Mlsa) mice were repeatedly injected with monoclonal anti-V beta 6 prior to and during syngeneic pregnancy. The offspring were born non-viable or died within 24 h. Continued injections into the mother resulted in abortions and conception eventually ceased altogether. Antisera from hyperimmunized mothers, when injected into the neonatal offspring of untreated AKR mothers, also had a lethal effect within 4 to 10 days after injection. Some mice survived for several weeks. All injected neonates developed a graft-versus-host disease (GVHD)-like syndrome characterized by runting, presence of skin lesions and weight loss. Antiserum injected in a diluted form caused similar but less severe symptoms. FACS (fluorescence-activated cell sorter) analysis of lymphocyte profiles of these mice revealed significant increases in the L3T4+ and Lyt-2+ T lymphocyte subsets; the number of V beta 6 T cells also increased. However Histopathological findings and mechanisms of the GVHD-like syndrome in these mice are discussed.

Peripheral T cell activation and deletion induced by transfer of lymphocyte subsets expressing endogenous or exogenous mouse mammary tumor virus

Murine T cell reactivity with products of the minor lymphocyte stimulatory (Mls) locus correlates with the expression of particular variable (V) domains of the T cell receptor (TCR) beta chain. It was recently demonstrated that Mls antigens are encoded by an open reading frame (ORF) in the 3' long terminal repeat of either endogenous or exogenous mouse mammary tumor virus (MMTV). Immature thymocytes expressing reactive TCR-V beta domains are clonally deleted upon exposure to endogenous Mtv's. Mature T cells proliferate vigorously in response to Mls-1a (Mtv-7) in vivo, but induction of specific anergy and deletion after exposure to Mtv-7-expressing cells in the periphery has also been described. We show here that B cells and CD8+ (but not CD4+) T cells from Mtv-7+ mice efficiently induce peripheral deletion of reactive T cells upon transfer to Mtv-7- recipients, whereas only B cells stimulate specific T cell proliferation in vivo. In contrast to endogenous Mtv-7, transfer of B, CD4+, or CD8+ lymphocyte subsets from mice maternally infected with MMTV(SW), an infectious homologue of Mtv-7, results in specific T cell deletion in the absence of a detectable proliferative response. Finally, we show by secondary transfers of infected cells that exogenous MMTV(SW) is transmitted multidirectionally between lymphocyte subsets and ultimately to the mammary gland. Collectively our data demonstrate heterogeneity in the expression and/or presentation of endogenous and exogenous MMTV ORF by lymphocyte subsets and emphasize the low threshold required for induction of peripheral T cell deletion by these gene products.

Clonal anergy blocks in vivo growth of mature T cells and can be reversed in the absence of antigen

Experiments in various models have indicated that immunological tolerance can result from the physical elimination (deletion) of reactive lymphocytes as well as from anergy. We have previously reported that mature CD4-CD8+ T cells when confronted with their antigen can proliferate extensively but are finally eliminated or become intrinsically anergic such that remaining cells are refractory to stimulation by any T cell receptor ligands, even in the presence of exogenous interleukin 2. Here we show that in vivo the anergy can be reversed in the absence of antigen, such that the cells are then able to proliferate extensively in vivo to a new challenge with the antigen in question.

Virus persistence in acutely infected immunocompetent mice by exhaustion of antiviral cytotoxic effector T cells

Viruses that are non- or poorly cytopathic have developed various strategies to avoid elimination by the immune system and to persist in the host. Acute infection of adult mice with the noncytopathic lymphocytic choriomeningitis virus (LCMV) normally induces a protective cytotoxic T-cell response that also causes immunopathology. But some LCMV strains (such as DOCILE (LCMV-D) or Cl-13 Armstrong (Cl-13)) derived from virus carrier mice tend to persist after acute infection of adult mice without causing lethal immunopathological disease. Tendency to persist correlates with tropism, rapidity of virus spread and virus mutations. We report here that these LCMV isolates may persist because they induce most of the specific antiviral CD8+ cytotoxic T cells so completely that they all disappear within a few days and therefore neither eliminate the virus nor cause lethal immunopathology. The results illustrate that partially and sequentially induced (protective) immunity or complete exhaustion of T-cell immunity (high zone tolerance) are quantitatively different points on the scale of immunity; some viruses exploit the latter possibility to persist in an immunocompetent host.

Subversion of host immune responses by viral superantigens

Recent experiments with mouse mammary tumor virus indicate that expression of a virally encoded superantigen by B cells and its subsequent recognition by T cells are essential steps for amplification of infection and virus transmission. Preliminary results suggest that superantigens may also be expressed during retroviral infection in humans.