Cytotoxic T lymphocyte-associated antigen 4 plays an essential role in the function of CD25(+)CD4(+) regulatory cells that control intestinal inflammation

The early IL-4 response to Leishmania major and the resulting Th2 cell maturation steering progressive disease in BALB/c mice are subject to the control of regulatory CD4+CD25+ T cells

Susceptibility and development of Th2 cells in BALB/c mice infected with Leishmania major result from early IL-4 production by Vbeta4Valpha8 CD4+ T cells in response to the Leishmania homolog of mammalian RACK1 Ag. A role for CD4+CD25+ regulatory T cells in the control of this early IL-4 production was investigated by depleting in vivo this regulatory T cell population. Depletion induced an increase in the early burst of IL-4 mRNA in the draining lymph nodes of BALB/c mice, and exacerbated the course of disease with higher levels of IL-4 mRNA and protein in their lymph nodes. We further showed that transfer of 10(7) BALB/c spleen cells that were depleted of CD4+CD25+ regulatory T cells rendered SCID mice susceptible to infection and allowed Th2 differentiation while SCID mice reconstituted with 10(7) control BALB/c spleen cells were resistant to infection with L. major and developed a Th1 response. Treatment with a mAb against IL-4 upon infection with L. major in SCID mice reconstituted with CD25-depleted spleen cells prevented the development of Th2 polarization and rendered them resistant to infection. These results demonstrate that CD4+CD25+ regulatory T cells play a role in regulating the early IL-4 mRNA and the subsequent development of a Th2 response in this model of infection.

Pathogen-specific regulatory T cells provoke a shift in the Th1/Th2 paradigm in immunity to infectious diseases

Current dogma suggests that immunity to infection is controlled by distinct type 1 (Th1) and type 2 (Th2) subpopulations of T cells discriminated on the basis of cytokine secretion and function. However, a further subtype of T cells, with immunosuppressive function and cytokine profiles distinct from either Th1 or Th2 T cells, termed regulatory T (Tr) cells has been described. Although considered to have a role in the maintenance of self-tolerance, recent studies suggest that Tr cells can be induced against bacterial, viral and parasite antigens in vivo and might prevent infection-induced immunopathology or prolong pathogen persistence by suppressing protective Th1 responses. These observations have significant implications for our understanding of the role of T cells in immunity to infectious diseases and for the development of new therapies for immune-mediated disorders.

The subpopulation of CD4+CD25+ splenocytes that delays adoptive transfer of diabetes expresses L-selectin and high levels of CCR7

Recently, CD4(+)CD25(+) T cells have been implicated in the control of diabetes, suggesting that the inflamed islets of Langerhans in prediabetic NOD mice are under peripheral immune surveillance. Here we show that CD4(+)CD25(+) splenocytes inhibit diabetes in cotransfer with islet-infiltrating cells. Furthermore, CD62L expression is necessary for this disease-delaying effect of CD4(+)CD25(+) cells in vivo, but not for their suppressor function in vitro. We demonstrate that the CD4(+)CD25(+)CD62L(+) splenocytes express CCR7 at high levels and migrate toward secondary lymphoid tissue chemokine and ELC (macrophage-inflammatory protein-3beta), lymphoid chemokines, whereas CD4(+)CD25(+)CD62L(-) splenocytes preferentially express CCR2, CCR4, and CXCR3 and migrate toward the corresponding inflammatory chemokines. These data demonstrate that CD4(+)CD25(+)CD62L(+), but not CD4(+)CD25(+)CD62L(-), splenocytes delay diabetes transfer, and that CD4(+)CD25(+) suppressor T cells are comprised of at least two subpopulations that behave differently in cotransfer in vivo and express distinct chemokine receptor and chemotactic response profiles despite demonstrating equivalent suppressor functions in vitro.

UVB-irradiated dendritic cells induce nonproliferating, regulatory type T cells

It is well established that low-dose UVB radiation inhibits the antigen-presenting cell (APC) function of murine Langerhans cells in vivo and converts them from immunogenic to tolerogenic APC. Recently, we have shown that UVB-irradiated murine bone marrow-derived dendritic cells (UVB-DC) suppressed proliferation of naive and primed T cells, but tolerized primed T cells only. To examine the underlying mechanism for these differences, naive OVA(323-339)-peptide-specific, TCR-transgenic T cells from DO11.10 mice were analyzed following coculture with unirradiated DC or UVB-DC. First, we found that UVB-DC inhibit OVA-specific T cell proliferation UVB dose and antigen dose dependently. Analysis of T cells cocultured with both, unirradiated and UVB-DC, revealed an activated T cell phenotype with increased expression of CD25 and CD69 by FACS. Supernatants harvested from cocultures with UVB-DC showed reduced levels of IFN-gamma, IL-2 and IL-4, but not TGF-beta, compared with unirradiated DC as determined by ELISA. Furthermore, these T cells did not proliferate upon restimulation. Interestingly, addition of these nonproliferating T cells to cocultures of naive T cells and freshly prepared unirradiated DC inhibited T cell proliferation depending on the number of added nonproliferating T cells. Also, in supernatants, increased levels of TGF-beta were found. Therefore, our data indicate that UVB-DC propagate T cells with a regulatory function. Since regulatory T cells are characterized by enhanced TGF-beta secretion and increased CTLA-4 expression, we currently investigate the role of CTLA-4 phenotypically and functionally. In conclusion, we have shown that UVB-DC inhibit proliferation of naive OVA-specific T cells. These T cells, exhibiting an activated phenotype and increased TGF-beta production, suppress proliferation of naive T cells cocultured with unirradiated DC. These results suggest that UVB-DC induce nonproliferating, regulatory type T cells.

Use of a non-depleting anti-CD4 antibody to modulate the immune response to coagulation factors VIII and IX

The generation of antibodies to therapeutic factors VIII or IX is a major problem in the management of haemophilia and places potential limitations on the application of gene therapy. We have investigated the administration of a non-depleting anti-CD4 antibody for modulation of the immune response to human recombinant coagulation factors VIII and IX. In mice given these clotting factors, co-administration of anti-CD4 antibody significantly reduced the appearance of factor-specific antibodies. These data provide evidence that the neutralizing antibody response to exogenous coagulation factors may be controllable if non-depleting anti-CD4 antibody is co-administered at the time of initial replacement therapy.

Bacteria-triggered CD4(+) T regulatory cells suppress Helicobacter hepaticus-induced colitis

We have previously demonstrated that interleukin (IL)-10-deficient (IL-10 knockout [KO]) but not wild-type (WT) mice develop colitis after infection with Helicobacter hepaticus. Here, we show that infected recombination activating gene (RAG) KO mice develop intestinal inflammation after reconstitution with CD4(+) T cells from IL-10 KO animals and that the cotransfer of CD4(+) T cells from H. hepaticus-infected but not uninfected WT mice prevents this colitis. The disease-protective WT CD4(+) cells are contained within the CD45RB(low) fraction and unexpectedly were found in both the CD25(+) and the CD25(-) subpopulations of these cells, their frequency being higher in the latter. The mechanism by which CD25(+) and CD25(-) CD45RB(low) CD4(+) cells block colitis involves IL-10 and not transforming growth factor (TGF)-beta, as treatment with anti-IL-10R but not anti-TGF-beta monoclonal antibody abrogated their protective effect. In vitro, CD45RB(low) CD4(+) cells from infected WT mice were shown to produce IL-10 and suppress interferon-gamma production by IL-10 KO CD4(+) cells in an H. hepaticus antigen-specific manner. Together, our data support the concept that H. hepaticus infection results in the induction in WT mice of regulatory T cells that prevent bacteria-induced colitis. The induction of such cells in response to gut flora may be a mechanism protecting normal individuals against inflammatory bowel disease.

Re-establishing peripheral tolerance in the absence of CTLA-4: complementation by wild-type T cells points to an indirect role for CTLA-4

CTLA-4 plays an important role in the down-regulation of activated T cells and in the establishment of peripheral tolerance. It has been hypothesized that CTLA-4 on the cell surface signals directly into T cells during primary immune responses, resulting in intrinsic T cell down-regulation. It is not known, however, whether CTLA-4 directly inhibits the less intense activating signals received by autoreactive T cells in the periphery. We investigated whether CTLA-4 acts intrinsically upon self-reactive cells in vivo, or whether it inhibits autoreactive cells indirectly, in a non-cell autonomous manner. The adoptive transfer of CTLA-4-deficient splenocytes or Thy 1(+) cells into recombinase-activating gene 2-deficient mice resulted in fatal inflammation and tissue destruction similar to that seen in CTLA-4-deficient mice. When an equivalent number of splenocytes or Thy 1(+) cells from wild-type animals was transferred with the CTLA-4-deficient cells, recipient mice survived indefinitely. Since CTLA-4 was absent in the T cells responsible for the inflammatory phenotype, the down-regulation of these autoreactive cells must have been facilitated indirectly by wild-type Thy 1(+) cells. In addition, a rapid reduction in the ratio of CTLA-4-deficient to wild-type cells was observed. We propose two possible indirect mechanisms by which CTLA-4 may function in the establishment and maintenance of peripheral tolerance.

Streptococcus sanguis modulates type II collagen-induced arthritis in DBA/1J mice

Native type II collagen is tolerogenic when given orally or i.p. to DBA/1J mice and induces autoimmune arthritis when given s.c. in CFA. The tolerogenic epitope is contained in cyanogen bromide fragment 11 (CB11) and is structurally mimicked by PGEQGPK within the platelet aggregation-associated protein (PAAP) on Streptococcus sanguis. To learn whether S. sanguis modulates transmucosally the Ag-specific development of autoimmune arthritis, DBA/1J pups were given live S. sanguis, CB11, or type II collagen intragastrically. Feeding S. sanguis at 6 days postpartum delayed the onset of arthritis, and reduced the rate, final severity, and percentage of affected limbs. Next, PAAP(+) S. sanguis and type II collagen were tested for T cell cross-reactivity. T cells primed with the tolerogenic epitope of type II collagen proliferated more when incubated with PAAP(+) S. sanguis than with PAAP(-) Streptococcus gordonii or type II collagen, suggesting an Ag-specific transmucosal tolerogenic effect. In neonatal mice, therefore, bacterial surface Ags that mimic self can transmucosally stimulate Ag-specific inhibitory T cells. In adult mice immunized with type II collagen, these Ag-specific inhibitory T cells manifest later as attenuated arthritis. The PAAP(+) S. sanguis appear to activate adult memory, rather than naive, type II collagen-specific T cells, suggesting that systemic challenge with commensal self-mimicking microorganisms may perpetuate existing autoimmunity, but not initiate autorecognition.

Phenotype, localization, and mechanism of suppression of CD4(+)CD25(+) human thymocytes

Phenotypic markers, localization, functional activities, and mechanisms of action in vitro of CD4(+)CD25(+) T cells, purified from postnatal human thymuses, were investigated. These cells showed poor or no proliferation in mixed lymphocyte culture (MLC), and suppressed in a dose-dependent fashion the proliferative response to allogeneic stimulation of CD4(+)CD25(-) thymocytes. Virtually all CD4(+)CD25(+) thymocytes constitutively expressed cytoplasmic T lymphocyte antigen (CTLA)-4, surface tumor necrosis factor type 2 receptor (TNFR2), and CCR8. They prevalently localized to perivascular areas of fibrous septa and responded to the chemoattractant activity of CCL1/I-309, which was found to be produced by either thymic medullary macrophages or fibrous septa epithelial cells. After polyclonal activation, CD4(+)CD25(+) thymocytes did not produce the cytokines interleukin (IL)-2, IL-4, IL-5, IL-13, interferon gamma, and only a very few produced IL-10, but all they expressed on their surface CTLA-4 and the majority of them also transforming growth factor (TGF)-beta1. The suppressive activity of these cells was contact dependent and associated with the lack of IL-2 receptor (IL-2R) alpha-chain (CD25) expression in target cells. Such a suppressive activity was partially inhibited by either anti-CTLA-4 or anti-TGF-beta1, and was completely blocked by a mixture of these monoclonal antibodies, which were also able to restore in target T cells the expression of IL-2R alpha-chain and, therefore, their responsiveness to IL-2. These data demonstrate that CD4(+)CD25(+) human thymocytes represent a population of regulatory cells that migrate in response to the chemokine CCL1/I-309 and exert their suppressive function via the inhibition of IL-2R alpha-chain in target T cells, induced by the combined activity of CTLA-4 and membrane TGF-beta1.

Donor-type CD4(+)CD25(+) regulatory T cells suppress lethal acute graft-versus-host disease after allogeneic bone marrow transplantation

Acute graft-versus-host disease (aGVHD) is still a major obstacle in clinical allogeneic bone marrow (BM) transplantation. CD4(+)CD25(+) regulatory T (T(reg)) cells have recently been shown to suppress proliferative responses of CD4(+)CD25(-) T cells to alloantigenic stimulation in vitro and are required for ex vivo tolerization of donor T cells, which results in their reduced potential to induce aGVHD. Here we show that CD4(+)CD25(+) T cells isolated from the spleen or BM of donor C57BL/6 (H-2(b)) mice that have not been tolerized are still potent inhibitors of the alloresponse in vitro and of lethal aGVHD induced by C57BL/6 CD4(+)CD25(-) T cells in irradiated BALB/c (H-2(d)) hosts in vivo. The addition of the CD4(+)CD25(+) T(reg) cells at a 1:1 ratio with responder/inducer CD4(+)CD25(-) T cells resulted in a >90% inhibition of the mixed leukocyte reaction and marked protection from lethal GVHD. This protective effect depended in part on the ability of the transferred CD4(+)CD25(+) T cells to secrete interleukin 10 and occurred if the T(reg) cells were of donor, but not host, origin. Our results demonstrate that the balance of donor-type CD4(+)CD25(+) T(reg) and conventional CD4(+)CD25(-) T cells can determine the outcome of aGVHD.

About CD4pos CD25pos regulatory cells

Autoreactive cells that escape from thymic negative selection are either anergized or counter-regulated in the peripheral lymphoid organs by regulatory T (Treg) cells. Most investigated Treg cells are CD4pos cells expressing the alpha chain of the IL-2 receptor (CD25). Absence of this particular population leads to the development of a wide range of autoimmune disorders, suggesting a critical role for CD4pos CD25pos cells in the maintenance of normal immune homeostasis. Numerous studies have aimed at unraveling the mechanisms of regulation, focusing mainly on naturally occurring Treg cells (generated in naive animals) and regulation of CD4pos autoreactive cells. In contrast, generation following antigenic priming of CD4pos CD25pos Treg cells with non-self (viral) antigen specificity and regulation of virus-activated CD4pos and CD8pos cells remain to be investigated. In this review, we describe the data collected over the past few years of intense focus on CD4pos CD25pos Treg cells and present our approach to investigate the generation of antigen-specific Treg cells during the course of an anti-viral immune response.

Balancing protective immunity and immunopathology

The immune system is fighting a constant war against pathogens in its own territory. This requires a potent arsenal for efficient control of pathogens but also requires tight regulatory mechanisms in order to avoid excessive collateral damage. Maintaining equilibrium is the daily challenge of the immune system. Interactions between pathogens, antigen-presenting cells (APCs) and lymphocytes are critical in this balancing act. Of particular importance for the generation of protective immune responses is the induction of activation programs in APCs directly by pathogens or by T cell derived factors, such as CD40L, RANKL or cytokines. In order to counterbalance overshooting immune responses, T cells and APCs secrete anti-inflammatory cytokines that are key for maintaining a healthy balance between protection and immunopathology.

Origin of regulatory T cells with known specificity for antigen

T cell receptor agonists can induce the differentiation of regulatory T (T(R)) cells. We report here that the immunoglobulin kappa-controlled expression of an agonist in different cell types correlated with the phenotype of the generated T(R) cells. We found that aberrant expression on thymic stroma yielded predominantly CD4(+)CD25(+) T(R) cells, which--under physiological conditions--may be induced by ectopically expressed organ-specific antigens and thus prevent organ-specific autoimmunity. Expression of the agonist antigen by nonactivated hematopoietic cells produced mostly CD4(+)CD25(-) T(R) cells. This subset can be derived from mature monospecific T cells without "tutoring" by other T cells and can be generated in the absence of a functioning thymus. Suppression of CD4(+) T cell proliferative responses by both CD25(+) and CD25(-) subsets was interleukin 10 (IL-10) independent and was overcome by IL-2. These data suggest that distinct pathways can be exploited to interfere with unwanted immune responses.

The interaction properties of costimulatory molecules revisited

B7-1 and B7-2 are generally thought to have comparable structures and affinities for their receptors, CD28 and CTLA-4, each of which is assumed to be bivalent. We show instead (1) that B7-2 binds the two receptors more weakly than B7-1, (2) that, relative to its CTLA-4 binding affinity, B7-2 binds CD28 2- to 3-fold more effectively than B7-1, (3) that, unlike B7-1, B7-2 does not self-associate, and (4) that, in contrast to CTLA-4 homodimers, which are bivalent, CD28 homodimers are monovalent. Our results indicate that B7-1 markedly favors CTLA-4 over CD28 engagement, whereas B7-2 exhibits much less bias. We propose that the distinct structures and binding properties of B7-1 and B7-2 account for their overlapping but distinct effects on T cell responses.

Histone peptide-induced nasal tolerance: suppression of murine lupus

Induced mucosal tolerance has been shown to be beneficial in preventing or treating a number of murine and human autoimmune disorders. However, this particular form of therapy has not been thoroughly tested in systemic lupus erythematosus. In this study, we investigated the conditions for induction of nasal tolerance using a histone peptide named H471 expressing a dominant T cell epitope in the histone protein H4 of mononucleosome in lupus-prone SNF(1) female mice. We also tested the effect of chronic peptide nasal treatment on the development of autoimmune reactivities in these mice. Results demonstrated that a dose-dependent nasal tolerance to peptide H471 can be achieved before or after peptide sensitization in SNF(1) mice. In addition, tolerance to mononucleosomes was induced by nasal instillation of SNF(1) mice with H471. This was accompanied by an increase in IL-10 and suppression of IFN-gamma production by lymph node cells. Suppression of Th1-type cytokines was also observed in SNF(1) mice that were nasally administered with H471 before intradermal injection with the peptide. Finally, chronic nasal instillation of mice with the H471 peptide not only suppressed the development of autoantibodies, but also altered the severity of glomerulonephritis in lupus-prone SNF(1) mice.

CD4(+)CD25(+) regulatory T cells can mediate suppressor function in the absence of transforming growth factor beta1 production and responsiveness

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of T cell activation in vitro. Their mechanism of suppression remains unknown, but most in vitro studies suggest that it is cell contact-dependent and cytokine independent. The role of TGF-beta1 in CD4(+)CD25(+) suppressor function remains unclear. While most studies have failed to reverse suppression with anti-transforming growth factor (TGF)-beta1 in vitro, one recent study has reported that CD4(+)CD25(+) T cells express cell surface TGF-beta1 and that suppression can be completely abrogated by high concentrations of anti-TGF-beta suggesting that cell-associated TGF-beta1 was the primary effector of CD4(+)CD25(+)-mediated suppression. Here, we have reevaluated the role of TGF-beta1 in CD4(+)CD25(+)-mediated suppression. Neutralization of TGF-beta1 with either monoclonal antibody (mAb) or soluble TGF-betaRII-Fc did not reverse in vitro suppression mediated by resting or activated CD4(+)CD25(+) T cells. Responder T cells from Smad3(-/-) or dominant-negative TGF-beta type RII transgenic (DNRIITg) mice, that are both unresponsive to TGF-beta1-induced growth arrest, were as susceptible to CD4(+)CD25(+)-mediated suppression as T cells from wild-type mice. Furthermore, CD4(+)CD25(+) T cells from neonatal TGF-beta1(-/-) mice were as suppressive as CD4(+)CD25(+) from TGF-beta1(+/+) mice. Collectively, these results demonstrate that CD4(+)CD25(+) suppressor function can occur independently of TGF-beta1.

CTLA-4: new insights into its biological function and use in tumor immunotherapy

The discovery of multiple costimulatory cell surface molecules that influence the course of T cell activation has increased our appreciation of the complexity of the T cell response. It remains clear, however, that CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) are the critical costimulatory receptors that determine the early outcome of stimulation through the T cell antigen receptor (TCR). Details of how the T cell integrates TCR stimulation with the costimulatory signals of CD28 and the inhibitory signals of CTLA-4 remain to be established, but unique features of the cell biology of CTLA-4 provide important insights into its function. We summarize here recent findings that suggest a previously unrecognized role for CTLA-4 in the regulation of T cell responses. We also describe preclinical and clinical results that indicate manipulation of CTLA-4 has considerable promise as a strategy for the immunotherapy of cancer.

Reprogramming the immune system

The immune system is organized so as to react to pathogens without risking damage to self. Harnessing those processes that prevent self-reactivity will have enormous potential in clinical medicine. This review outlines the efforts of this laboratory over the last 25 years to exploit tolerance so as to reprogram the immune system for therapeutic purposes.

Murine Peyer's patches favor development of an IL-10-secreting, regulatory T cell population

Peyer's patches (PP) are believed to be the principal sites for induction of tolerance to Ags from food and commensal flora, yet the phenotype of T cells activated within the PP is largely unexplored. We hypothesize that exposure to Ags within the PP promotes differentiation of T cells with immunoregulatory functions. Cytokine production and cell surface marker expression of murine PP mononuclear cells (MC) are compared with those from mesenteric lymph nodes and peripheral lymph nodes (PLN). In response to stimulation through the TCR/CD3 complex, PP MC exhibit vigorous proliferation, modest production of IL-2, and significantly elevated synthesis of IL-10. Exogenous IL-12 enhances both IL-10 and IFN-gamma secretion by activated PP MC. Cell surface marker analysis reveals that PP T cells consist of activated and memory subpopulations compared with the predominantly naive T cells identified in the PLN and mesenteric lymph nodes. Upon stimulation, only CD45RB(low)CD4(+) PP T cells produce IL-10, whereas secretion of IL-2, IL-4, and IFN-gamma was not detected. Furthermore, PP MC, but not PLN MC, stimulated through the TCR/CD3 complex suppress proliferation of purified PLN T cells in vitro, evidence for a regulatory function among PP lymphocytes. We conclude that PP favor differentiation of an IL-10-producing, regulatory CD45RB(low)CD4(+) T cell population and that inhibition of T cell proliferation by activated PP MC may reflect regulatory activity consistent with T regulatory cells.

Memory Th2 effector cells can develop in the absence of B7-1/B7-2, CD28 interactions, and effector Th cells after priming with an intestinal nematode parasite

B7-1/B7-2 interactions are required for many Th2-cell mediated primary immune responses including the response that follows infection with the intestinal nematode parasite, Heligmosomoides polygyrus. However, few studies have examined the role of B7-1/B7-2/CD28 interactions in the development of a Th2 memory immune response. We examined the development of the memory Th2 response to H. polygyrus in BALB/c mice deficient in both B7-1 and B7-2 (B7-1/B7-2(-/-)) and in BALB/c mice deficient in CD28 (CD28(-/-)). Following primary inoculation with H. polygyrus, adult worms in the gut were cleared with an anti-helminthic drug and mice were subsequently challenge-inoculated with H. polygyrus larvae. The memory Th2 response is readily distinguished by its inhibitory effect on adult worm maturation, resulting in marked reductions in adult worm egg production that are not observed during the primary immune response. Following H. polygyrus challenge inoculation, comparable decreases in egg production and similar increases in mesenteric lymph node cell IL-4 production were observed in B7-1/B7-2(-/-) and B7-1/B7-2(+/+) mice. However, elevations in total serum IgG1 and IgE were reduced, while increases in serum Ag-specific IgG1 and IgE and germinal center formation were blocked in H. polygyrus-challenged B7-1/B7-2(-/-) mice. In contrast, in H. polygyrus-challenged CD28(-/-) mice, marked elevations in Ag-specific IgG1 and IgE and increased germinal center formation were observed. The results of these studies demonstrate that effector Th2 memory cells that produce IL-4 and mediate host defense can develop when B7-1/B7-2 interactions, and associated effector Th2 cell development, are blocked during priming. However, humoral immunity is impaired and differentially affected in B7-1/B7-2(-/-) mice and CD28(-/-) mice following H. polygyrus challenge.

The lymphoproliferative defect in CTLA-4-deficient mice is ameliorated by an inhibitory NK cell receptor

T-cell responses are regulated by activating and inhibiting signals. CD28 and its homologue, cytotoxic T-lymphocyte antigen 4 (CTLA-4), are the primary regulatory molecules that enhance or inhibit T-cell activation, respectively. Recently it has been shown that inhibitory natural killer (NK) cell receptors (NKRs) are expressed on subsets of T cells. It has been proposed that these receptors may also play an important role in regulating T-cell responses. However, the extent to which the NKRs modulate peripheral T-cell homeostasis and activation in vivo remains unclear. In this report we show that NK cell inhibitory receptor Ly49A engagement on T cells dramatically limits T-cell activation and the resultant lymphoproliferative disorder that occurs in CTLA-4-deficient mice. Prevention of activation and expansion of the potentially autoreactive CTLA-4(-/-) T cells by the Ly49A-mediated inhibitory signal demonstrates that NKR expression can play an important regulatory role in T-cell homeostasis in vivo. These results demonstrate the importance of inhibitory signals in T-cell homeostasis and suggest the common biochemical basis of inhibitory signaling pathways in T lymphocytes.

Specificity requirements for selection and effector functions of CD25+4+ regulatory T cells in anti-myelin basic protein T cell receptor transgenic mice

CD25(+)4(+) regulatory T cells (T(reg)) play an indispensable role in preventing autoimmunity. Little is known, however, about the antigen specificities required for their development and effector functions. Mice transgenic for an anti-myelin basic protein (MBP) T cell antigen receptor (TCR) spontaneously develop experimental autoimmune encephalomyelitis (EAE) when deficient for the RAG-1 gene (T/R(-)), whereas RAG-1-competent transgenic animals (T/R(+)) remain healthy, protected by CD4(+) T(reg)-expressing endogenous TCRs. We have now investigated the role and specificity of CD25(+)4(+) T(reg) in this system. The results show that T/R(+) animals contain MBP-specific suppressive CD25(+)4(+) cells, whereas T/R(-) do not. Adoptive transfer of CD25(+)4(+) cells from nontransgenic or T/R(+) donors into T/R(-) mice prevented the development of EAE. Surprisingly, transfer of nontransgenic CD25(+)4(+) cells purified from T/R(+) donors conferred only a limited protection, possibly because of their restricted repertoire diversity that we demonstrate here. Absence of transgenic CD25(+)4(+) cells in animals deficient for endogenous TCRalpha chains and analyses of endogenous TCR gene expression in subsets of CD4(+) cells from T/R(+) mice demonstrate that development of transgenic MBP-specific CD25(+)4(+) T(reg) depends on the coexpression of endogenous TCRalpha chains. Taken together, these results indicate that specificity to MBP is required for effector functions but is not sufficient for thymic selection/commitment of CD25(+)4(+) T(reg) preventing EAE.

The immunology of mucosal models of inflammation

In recent years the status of the inflammatory bowel diseases (IBDs) as canonical autoimmune diseases has risen steadily with the recognition that these diseases are, at their crux, abnormalities in mucosal responses to normally harmless antigens in the mucosal microflora and therefore responses to antigens that by their proximity and persistence are equivalent to self-antigens. This new paradigm is in no small measure traceable to the advent of multiple models of mucosal inflammation whose very existence is indicative of the fact that many types of immune imbalance can lead to loss of tolerance for mucosal antigens and thus inflammation centered in the gastrointestinal tract. We analyze the immunology of the IBDs through the lens of the murine models, first by drawing attention to their common features and then by considering individual models at a level of detail necessary to reveal their individual capacities to provide insight into IBD pathogenesis. What emerges is that murine models of mucosal inflammation have given us a road map that allows us to begin to define the immunology of the IBDs in all its complexity and to find unexpected ways to treat these diseases.

CD4+CD25+ T lymphocytes in human tonsils suppress the proliferation of CD4+CD25- tonsil cells

Animal studies define CD4+CD25+ T cells as a subset that protect against autoimmune inflammation. We wanted to investigate whether CD4+CD25+ T cells from patients with recurrent tonsillitis could suppress the proliferation of other tonsil cells, in vitro, as this immunological tissue also may serve as a model for chronic inflammation. Tonsil CD4+CD25+ cells markedly suppressed the proliferation of CD4+CD25- T cells in Concanavalin A-stimulated cocultures compared with cultures containing CD4+CD25- T cells only. The suppression exerted by the CD4+CD25+ cells was abrogated if these cells were irradiated before coculture or if interleukin (IL)-2 was added to the culture medium. CD4+CD25+ T cells proliferated poorly in response to mitogen, when cultured alone. Substitution with CD4+CD25+ T cells isolated from peripheral blood, enriched by similar methods, did not downregulate the proliferation of CD4+CD25- responder cells from tonsils. The augmented suppressive ability of tonsil CD4+CD25+ T cells compared with cells of this phenotype from blood, on CD4+CD25- responder cells from tonsils, suggests that there may be a functional difference between CD25+ cells from the two locations. In conclusion, CD4+CD25+ T cells from inflamed tonsils distinctly suppressed T-cell responses to mitogen in vitro, pointing to a regulatory role for CD4+CD25+ cells retrieved from inflammatory reactions in humans.

Both CD4(+)CD25(+) and CD4(+)CD25(-) regulatory cells mediate dominant transplantation tolerance

CD4(+)CD25(+) T cells have been proposed as the principal regulators of both self-tolerance and transplantation tolerance. Although CD4(+)CD25(+) T cells do have a suppressive role in transplantation tolerance, so do CD4(+)CD25(-) T cells, although 10-fold less potent. Abs to CTLA-4, CD25, IL-10, and IL-4 were unable to abrogate suppression mediated by tolerant spleen cells so excluding any of these molecules as critical agents of suppression. CD4(+)CD25(+) T cells from naive mice can also prevent rejection despite the lack of any previous experience of donor alloantigens. However, this requires many more naive than tolerized cells to provide the same degree of suppression. This suggests that a capacity to regulate transplant rejection pre-exists in naive mice, and may be amplified in "tolerized" mice. Serial analysis of gene expression confirmed that cells sorted into CD4(+)CD25(+) and CD4(+)CD25(-) populations were distinct in that they responded to TCR ligation with very different programs of gene expression. Further characterization of the differentially expressed genes may lead to the development of diagnostic tests to monitor the tolerant state.

Regulation of mucosal immune responses by recombinant interleukin 10 produced by intestinal epithelial cells in mice

BACKGROUND & AIMS

Interleukin (IL)-10 is a cytokine with anti-inflammatory properties. The aim of this study was to explore the effect of a site-specific delivery of IL-10 on intestinal immune responses.

METHODS

Transgenic mice were created in which IL-10 is expressed by the intestinal epithelial cells.

RESULTS

Transgenic mice showed a marked increase in the number of intraepithelial lymphocytes in the small intestine. Mucosal lymphocytes of transgenic animals produced fewer T helper type 1 cytokines than wild-type lymphocytes. By contrast, the production of transforming growth factor beta was increased. Moreover, the epithelial layer in transgenic mice was significantly enriched for CD4(+)CD25(+) T cells. Furthermore, transgenic mice had increased numbers of immunoglobulin A-producing B cells in the small intestine. These effects were local because splenic lymphocytes were not affected. Studies in models of inflammatory bowel disease showed that transgenic IL-10 was able to attenuate the acute colitis induced by dextran sodium sulfate administration or by adoptive transfer of CD4(+)CD45RB(high) splenocytes, with a modest effect on the chronic intestinal inflammation arising spontaneously in IL-10(-/-) mice.

CONCLUSIONS

These observations provide evidence for an in vivo lymphoepithelial cross talk, by which cytokines locally produced by epithelial cells can regulate immune responses in the intestine without systemic modifications.

CD4+ CD25+ suppressor T cells: more questions than answers

Several mechanisms control discrimination between self and non-self, including the thymic deletion of autoreactive T cells and the induction of anergy in the periphery. In addition to these passive mechanisms, evidence has accumulated for the active suppression of autoreactivity by a population of regulatory or suppressor T cells that co-express CD4 and CD25 (the interleukin-2 receptor alpha-chain). CD4+ CD25+ T cells are powerful inhibitors of T-cell activation both in vivo and in vitro. The enhancement of suppressor-cell function might prove useful for the treatment of immune-mediated diseases, whereas the downregulation of these cells might be beneficial for the enhancement of the immunogenicity of vaccines that are specific for tumour antigens.

Negative co-receptors on lymphocytes

The past year has seen significant advances in our understanding of critical roles of negative immunoregulatory signals delivered through the B7-CD28 superfamily in regulating T cell activation and tolerance. Structural data on CTLA-4 have provided novel insights into the inhibitory functions of CTLA-4. Initial characterization of the PD-1-PD-1-ligand pathway has revealed that this pathway can downregulate TCR- and CD28-mediated signals. Recent studies indicate that ICOS exerts distinct effects at different phases of an immune response: ICOS can inhibit as well as stimulate T cell responses.

Characterization of human CD25+ CD4+ T cells in thymus, cord and adult blood

CD4(+) CD25(+) regulatory T cells prevent organ-specific autoimmune diseases in various animal models. We analysed human lymphoid tissues to identify similar CD25(+) regulatory T cells. Adult peripheral blood contained two populations of CD4(+) T cells that expressed CD25 at different densities. The larger population (approximately 40%) expressed intermediate levels of CD25 (CD25(+)) and displayed a memory T-cell phenotype (CD45RA-/RO(+), CD45RB(low), CD95(+), CD62L(low), CD38(low)). The smaller population of cells (approximately 2%) expressed very high levels of CD25 (CD25(++)). In addition to the activation/memory T-cell antigens mentioned above they also expressed intracellular CD152 (CTLA-4) as well as enhanced levels of cell-surface CD122, similar to the murine CD4(+) CD25(+) regulatory counterpart. To exclude that the CD25(++) cells had not been recently primed by external antigen we analysed cord blood and thymus. CD25(++), CD152(+) and CD122(++) cells were present in paediatric thymus (10% of CD4(+) CD8(-) thymocytes) expressing signs of recent selection (CD69+) and in cord blood (5% of CD4(+) cells) where they showed a naive phenotype. In addition, cord blood contained a small population of CD25(+) cells (approximately 2% of CD4 T cells) that were CD152(-) and CD122(low) and displayed signs of activation. Together with published data that CD25(+) CD25(++) cells from the thymus and peripheral blood are regulatory, our results suggest that regulatory CD25(+) T cells leave the thymus in a naïve state and become activated in the periphery.

Transient CD44 variant isoform expression and reduction in CD4(+)/CD25(+) regulatory T cells in C3H/HeJ mice with alopecia areata

Alopecia areata, an autoimmune disease affecting anagen stage hair follicles, can be induced by grafting spontaneous alopecia areata affected skin to normal-haired C3H/HeJ mice. As the onset of alopecia areata can be significantly retarded by anti-CD44 variant isoform 10 treatment, it was interesting to explore the underlying disease mechanism. Two weeks after transplanting alopecia areata affected skin, expression of CD44 variant isoforms 3, 6, 7, and 10 was strikingly upregulated as compared with sham-grafted mice. By 6 wk after grafting, CD44 variant isoform levels had returned to normal, whereas in draining lymph nodes, CD44 variant isoform expression was slightly decreased. Leukocytes in the skin of mice with chronic alopecia areata expressed a hematopoietic isoform of CD44 and CD44 variant isoform 6 at an elevated level, but CD44 variant isoform 3 expression was reduced. Cytokine expression in leukocytes of chronic alopecia areata affected skin was higher than in normal-haired controls. Cytokine expression also increased postsurgery in sham and alopecia areata grafted mice, but remained elevated only in mice receiving alopecia areata affected skin. Finally, from the skin of mice with chronic alopecia areata and of mice transplanted with alopecia areata affected skin, an increased number of CD4(+) and CD8(+) cells, but a strongly decreased number of CD4(+)/CD25(+) regulatory T cells was recovered. Thus, expression of CD44 variant isoforms is important for the migration of leukocytes during the initial period of alopecia areata. CD44, however, is apparently not involved in the maintenance of the disease state, which is characterized by high cytokine expression levels, an increased number of CD4(+) and CD8+ cells, but a low level of CD4(+)/CD25(+) suppressor cells.

Escherichia coli heat-labile enterotoxin B subunit prevents autoimmune arthritis through induction of regulatory CD4+ T cells

OBJECTIVE

The receptor-binding B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a highly stable, nontoxic protein that is capable of modulating immune responses. This study was conducted to determine whether mucosal administration of EtxB can block collagen-induced arthritis (CIA) and to investigate the mechanisms involved.

METHODS

Clinical arthritis in DBA/1 mice was monitored following mucosal administration of EtxB on 4 occasions. The dependence of disease prevention on receptor binding by EtxB and the associated alterations to the immune response to type II collagen (CII) were assessed. Adoptive transfer experiments and lymph node cell cocultures were used to investigate the underlying mechanisms.

RESULTS

Both intranasal and intragastric delivery of EtxB were effective in preventing CIA; a 1-microg dose of EtxB was protective after intranasal administration. A non-receptor-binding mutant of EtxB failed to prevent disease. Intranasal EtxB lowered both the incidence and severity of arthritis when given either at the time of disease induction or 25 days later. EtxB markedly reduced levels of anti-CII IgG2a antibodies and interferon-gamma (IFNgamma) production while not affecting levels of IgG1, interleukin-4 (IL-4), or IL-10. Disease protection could be transferred by CD4+ T cells from treated mice, an effect that was abrogated upon depletion of the CD25+ population. In addition, CD4+CD25+ T cells from treated mice were able to suppress anti-CII IFNgamma production by CII-primed lymph node cells.

CONCLUSION

Mucosal administration of EtxB can be used to prevent or treat CIA. Modulation of the anti-CII immune response by EtxB is associated with a reduction in Th1 cell reactivity without a concomitant shift toward Th2. Instead, EtxB mediates its effects through enhancing the activity of a population of CD4+ regulatory T cells.

The infusion of ex vivo activated and expanded CD4(+)CD25(+) immune regulatory cells inhibits graft-versus-host disease lethality

Immune regulatory CD4(+)CD25(+) cells play a vital role in the induction and maintenance of self-tolerance and the prevention of autoimmunity. Recently, CD4(+)CD25(+) cells have been shown to be required for the ex vivo induction of tolerance to alloantigen via costimulatory blockade and to inhibit allogeneic skin graft rejection. Data presented here demonstrate that CD4(+)CD25(+) cells play an important role in graft-versus-host disease (GVHD) generation. Depletion of CD4(+)CD25(+) cells from the donor T-cell inoculum or in vivo CD25-depletion of the recipient before transplantation resulted in increased GVHD mediated by CD4(+) or whole T cells in several strain combinations irrespective of the total body irradiation conditioning regime. The infusion of freshly purified donor CD4(+)CD25(+) cells modestly inhibited GVHD when administered in equal numbers with whole CD4(+) cells. Because CD4(+)CD25(+) cells only account for 5% to 10% of the total CD4(+) population, the administration of high numbers of fresh donor CD4(+)CD25(+) cells may not be clinically practical. However, we found that large numbers of CD4(+)CD25(+) cells can be obtained by ex vivo activation and expansion. Cultured CD4(+)CD25(+) cells, administered in equal numbers with CD4(+) T cells or CD25-depleted whole T cells, resulted in significant inhibition of rapidly lethal GVHD. To our knowledge, this study is the first to demonstrate that activated, cultured CD4(+)CD25(+) cells can offer substantial protection in a relevant in vivo animal model of disease. These data have important ramifications for clinical bone marrow and solid organ transplantation. CD4(+)CD25(+) cells warrant consideration as an exciting new modality of cellular therapy for the inhibition of undesirable autologous and allogeneic responses.

Role for thymic and splenic regulatory CD4+ T cells induced by donor dendritic cells in allograft tolerance by LF15-0195 treatment

A 20-day treatment with LF15-0195, a deoxyspergualine analogue, induced allograft tolerance in a fully MHC-mismatched heart allograft model in the rat. Long-term allografts displayed minimal cell infiltration with no signs of chronic rejection. CD4+ spleen T cells from tolerant LF15-0195-treated recipients were able to suppress in vitro proliferation of allogeneic CD4+ T cells and to transfer tolerance to second syngeneic recipients, demonstrating dominant suppression by regulatory cells. A significant increase in the percentage of CD4+CD25+ T cells was observed in the thymus and spleen from tolerant LF15-0195-treated recipient. In vitro direct stimulation with donor APCs demonstrated that CD4+ regulatory T cells proliferated weakly and expressed low levels of IFN-gamma, IL-10, and IL-2. CD4+CD25+ cell depletion increased IL-2 production by CD4+CD25- thymic cells, but not splenic cells. Moreover, tolerance was transferable with splenic and thymic CD4+CD25+ cells, but also in 50% of cases with splenic CD4+CD25- cells, demonstrating that CD25 can be a marker for regulatory cells in the thymus, but not in the periphery. In addition, we presented evidences that donor APCs were required to induce tolerance and to expand regulatory CD4+ T cells. This study demonstrates that LF15-0195 treatment induces donor APCs to expand powerful regulatory CD4+CD25+/- T cells present in both the central and peripheral compartments.

Generation of CD4(+)CD25(+) regulatory T cells from autoreactive T cells simultaneously with their negative selection in the thymus and from nonautoreactive T cells by endogenous TCR expression

Normal T cell repertoire contains regulatory T cells that control autoimmune responses in the periphery. One recent study demonstrated that CD4(+)CD25(+) T cells were generated from autoreactive T cells without negative selection. However, it is unclear whether, in general, positive selection and negative selection of autoreactive T cells are mutually exclusive processes in the thymus. To investigate the ontogeny of CD4(+)CD25(+) regulatory T cells, neo-autoantigen-bearing transgenic mice expressing chicken egg OVA systemically in the nuclei (Ld-nOVA) were crossed with transgenic mice expressing an OVA-specific TCR (DO11.10). Ld-nOVA x DO11.10 mice had increased numbers of CD4(+)CD25(+) regulatory T cells in the thymus and the periphery despite clonal deletion. In Ld-nOVA x DO11.10 mice, T cells expressing endogenous TCR alpha beta chains were CD4(+)CD25(-) T cells, whereas T cells expressing autoreactive TCR were selected as CD4(+)CD25(+) T cells, which were exclusively dominant in recombination-activating gene 2-deficient Ld-nOVA x DO11.10 mice. In contrast, in DO11.10 mice, CD4(+)CD25(+) T cells expressed endogenous TCR alpha beta chains, which disappeared in recombination-activating gene 2-deficient DO11.10 mice. These results indicate that part of autoreactive T cells that have a high affinity TCR enough to cause clonal deletion could be positively selected as CD4(+)CD25(+) T cells in the thymus. Furthermore, it is suggested that endogenous TCR gene rearrangement might critically contribute to the generation of CD4(+)CD25(+) T cells from nonautoreactive T cell repertoire, at least under the limited conditions such as TCR-transgenic models, as well as the generation of CD4(+)CD25(-) T cells from autoreactive T cell repertoire.

Accumulation of human heat shock protein 60-reactive T cells in the gingival tissues of periodontitis patients

Heat shock protein 60s (hsp60) are remarkably immunogenic, and both T-cell and antibody responses to hsp60 have been reported in various inflammatory conditions. To clarify the role of hsp60 in T-cell responses in periodontitis, we examined the proliferative response of peripheral blood mononuclear cells (PBMC), as well as the cytokine profile and T-cell clonality, for periodontitis patients and controls following stimulation with recombinant human hsp60 and Porphyromonas gingivalis GroEL. To confirm the infiltration of hsp60-reactive T-cell clones into periodontitis lesions, nucleotide sequences within complementarity-determining region 3 of the T-cell receptor (TCR) beta-chain were compared between hsp60-reactive peripheral blood T cells and periodontitis lesion-infiltrating T cells. Periodontitis patients demonstrated significantly higher proliferative responses of PBMC to human hsp60, but not to P. gingivalis GroEL, than control subjects. The response was inhibited by anti-major histocompatibility complex class II antibodies. Analysis of the nucleotide sequences of the TCR demonstrated that human hsp60-reactive T-cell clones and periodontitis lesion-infiltrating T cells have the same receptors, suggesting that hsp60-reactive T cells accumulate in periodontitis lesions. Analysis of the cytokine profile demonstrated that hsp60-reactive PBMC produced significant levels of gamma interferon (IFN-gamma) in periodontitis patients, whereas P. gingivalis GroEL did not induce any skewing toward a type1 or type2 cytokine profile. In control subjects no significant expression of IFN-gamma or interleukin 4 was induced. These results suggest that periodontitis patients have human hsp60-reactive T cells with a type 1 cytokine profile in their peripheral blood T-cell pools.

A 1alpha,25-dihydroxyvitamin D(3) analog enhances regulatory T-cells and arrests autoimmune diabetes in NOD mice

Type 1 diabetes is a chronic progressive autoimmune disease characterized by mononuclear cell infiltration, dominated by interleukin-12 (IL-12)-dependent Th1 cells, of the pancreatic islets, with subsequent destruction of insulin-producing beta-cells. Here, we demonstrate that treatment of adult nonobese diabetic (NOD) mice with an analog of 1alpha,25-dihydroxyvitamin D(3), an immunomodulatory agent preventing dendritic cell maturation, decreases lipopolysaccharide-induced IL-12 and gamma-interferon production, arrests Th1 cell infiltration and progression of insulitis, and inhibits diabetes development at nonhypercalcemic doses. Arrest of disease progression is accompanied by an enhanced frequency in the pancreatic lymph nodes of CD4(+)CD25(+) regulatory T-cells that are able to inhibit the T-cell response to the pancreatic autoantigen insulinoma-associated protein 2 and to significantly delay disease transfer by pathogenic CD4(+)CD25(-) cells. Thus, a short treatment of adult NOD mice with an analog of 1,25-dihydroxyvitamin D(3) inhibits IL-12 production, blocks pancreatic infiltration of Th1 cells, enhances CD4(+)CD25(+) regulatory cells, and arrests the progression of type 1 diabetes, suggesting its possible application in the treatment of human autoimmune diabetes.

Current understanding of gastrointestinal immunoregulation and its relation to food allergy

Tolerance to food antigens induced via the gut ("oral tolerance") appears to be a rather robust adaptive immune mechanism. However, the neonatal period is particularly critical in terms of mucosal defense, with regard to infections and priming for allergic disease. This is so because the intestinal barrier function provided by secretory antibodies, as well as the immunoregulatory network, is poorly developed for a variable period after birth. Notably, the postnatal development of mucosal immune homeostasis depends on the establishment of a normal commensal microbial flora and also on adequate timing and dose of dietary antigens when first introduced. In this context, breastfeeding appears to exert both shielding and positive regulatory effects. Altogether, the intestinal immune system normally seems rather fit for tolerance induction against innocuous antigens because most children with food allergy "outgrow" their problems, whereas airway allergy tends to persist.

An established immune response against ovalbumin is suppressed by a transferable serum factor produced after ovalbumin feeding: a role of CD25+ regulatory cells

We have previously demonstrated that rats fed ovalbumin (OVA) develop a tolerogenic activity in serum, which upon transfer induces tolerance to OVA and suppression of the immune response to a bystander antigen. Here, we have extended these studies and analysed if the tolerogenic activity in serum could suppress an established immune response in the recipients. Rats were immunized with OVA, 4 and 1 week prior to the transfer of serum from either OVA-fed or control animals. Rats that received serum from OVA-fed donors had significantly lower delayed-type hypersensitivity (DTH) reaction against OVA 1 week after the serum transfer compared with the controls, and the levels of immunoglobulin (IgG) anti-OVA antibodies were significantly lower 2 and 4 weeks after serum transfer. Monomeric OVA in amounts corresponding to the OVA transferred with serum did not induce the reduction of DTH response or IgG anti-OVA antibody levels. In vitro, the proliferation of OVA-stimulated spleen cells, taken from recipients of tolerogenic serum, was significantly lower compared with spleen cells from the controls. The in vitro suppression seemed to be mediated by a population of CD25+ cells, because the removal of such cells from OVA-stimulated spleen cell suspensions resulted in increased proliferation in cultures from rats receiving tolerogenic serum. Our results showed that the tolerogenic serum factor can suppress an established immune response in recipient animals, possibly through induction of regulatory CD25+ cells. Whether this capacity might be used to influence chronic inflammatory conditions needs to be investigated.

Heavy chain ferritin activates regulatory T cells by induction of changes in dendritic cells

Heavy chain ferritin (H-ferritin) is a component of the iron-binding protein, ferritin. We have previously shown that H-ferritin inhibits anti-CD3-stimulated lymphocyte proliferation and that this was due to increased production of interleukin-10 (IL-10). In the present study we have shown that induction of IL-10 production was due to effects of H-ferritin on adherent antigen-presenting cells (APCs) in blood and monocyte-derived dendritic cells (MoDCs). IL-10 was produced by a subpopulation of CD4 T cells, which expressed the CD25 component of the IL-2 receptor and the CTLA-4 receptor characteristic of regulatory T cells. The changes induced in MoDCs were compared with those induced by CD40L and their significance tested by inhibition with monoclonal antibodies. These studies indicated that H-ferritin induced relatively greater expression of CD86 and B7-H1 on MoDCs and that monoclonal antibodies against their receptors, CTLA-4 and programmed death receptor-1 (PD-1), inhibited IL-10 production from the regulatory T cells. H-ferritin did not appear to induce direct production of the cytokines IL-2, IL-4, IL-6, IL-10, IL-12, or interferon-gamma from the DCs. These results are consistent with the thesis that H-ferritin induces B7-H1 and CD86 (B7-2) on APCs, which in turn induce IL-10 production from regulatory T cells. This is possibly one mechanism by which melanoma cells may induce changes in APCs in the vicinity of the tumor and result in suppression of immune responses by induction of regulatory T cells.

Cyclosporin A-induced autoimmunity in the rat: central versus peripheral tollerance

No abstract available

CD25+CD4+ regulatory T cells suppress CD4+ T cell-mediated pulmonary hyperinflammation driven by Pneumocystis carinii in immunodeficient mice

The CD4(+) T cell-mediated inflammatory response to Pneumocystis carinii (PC) critically contributes to the clinical severity of PC pneumonia. It has been suggested that lymphopenic conditions predispose individuals to this immunopathology, although the mechanisms remain poorly understood. Another set of evidence indicates that a subpopulation of CD4(+) T cells constitutively expressing the CD25 molecule prevent lymphopenia-induced autoimmunity and inflammatory bowel disease. We tested the ability of this CD25(+)CD4(+) population to regulate CD4(+) T cell-mediated inflammatory response to PC. Adoptive transfer of CD25(-)CD4(+) cells into PC-infected recombination-activating gene-2-deficient mice led to lethal pneumonia within 13 days post-transfer. PC infection appeared to trigger CD25(-)CD4(+) cells, since recipients with reduced PC load survived up to 5 weeks after transfer. In contrast, transfer of CD25(+)CD4(+) cells did not induce lethal pneumonia and prevented the development of the disease induced by CD25(-)CD4(+) cells. Furthermore, CD25(-)CD4(+) cells reduced the PC load in the lung, while CD25(+)CD4(+) cells suppressed this immune response. Our results indicate an essential role for CD25(+)CD4(+) T cells in the control of PC-driven immunopathology, and suggest that in immunocompromised hosts PC pneumonia may result from a deficiency in regulatory T cells.

Depletion of CD4+ CD25+ regulatory cells augments the generation of specific immune T cells in tumor-draining lymph nodes

Recent studies have identified a unique population of CD4+CD25+ regulatory T cells that is crucial for the prevention of spontaneous autoimmune diseases. Further studies demonstrated that depletion of CD4+CD25+ T cells enhances immune responses to nonself antigens. Because immune responses to malignant tumors are weak and ineffective, depletion of regulatory T cells has been reported to result in tumor regression. In the current study, using the weakly immunogenic MCA205 sarcoma and the poorly immunogenic B16/BL6/D5 (D5) melanoma, depletion of CD4+CD25+ T cells by the administration of anti-CD25 monoclonal antibodies (mAb), PC61 induced some tumor growth retardation, but all mice eventually succumbed to tumors. In our laboratory, immunotherapy by the transfer of tumor-immune T cells has demonstrated potent antitumor effects. A reliable source of tumor-reactive T cells has been lymph nodes (LN) draining progressive tumors. Therapeutic effector T cells can be generated by in vitro activation of draining LN cells with anti-CD3 mAb followed by culture in interleukin-2. In this system, PC61 mAb depletion of CD4+CD25+ T cells before or on day 8 of tumor growth resulted in increased sensitization in the draining LN. The therapeutic efficacy of activated tumor-draining LN cells from mAb depleted mice increased approximately three fold while maintaining specificity when tested in adoptive immunotherapy of established pulmonary metastases. Specific interferon-gamma secretion by LN T cells from mice treated with PC61 mAb 1 day before tumor inoculation increased significantly. However, this increase was not demonstrated with LN T cells from mice treated on day 8 despite their enhanced therapeutic reactivities. Our results indicate that although the antitumor immunity enhanced by the depletion of CD4+CD25+ T cells is insufficient to eradicate tumors, it augments the sensitization of immune T cells in the draining LN, thus, facilitating adoptive immunotherapy.

Cutting edge: Regulatory T cells from lung cancer patients directly inhibit autologous T cell proliferation

Active suppression by T regulatory cells plays an important role in the down-regulation of T cell responses to foreign and self-Ags. Thus far, the potential role of CD4(+)CD25(+) T cells in human tumors has not been reported. In this work we show that lung tumors contain large numbers of these cells and that they have constitutive high-level expression of CD152 (CTLA-4). Furthermore, the CD4(+)CD25(+) T cells mediate potent inhibition of autologous T cell proliferation. Finally, regulatory T cells from patient tumors failed to inhibit the proliferation of allogeneic T cells. Together these results suggest that the CD4(+)CD25(+) T cells found in lung tumors selectively inhibit the host immune response and therefore could contribute to the progression of lung cancer.

The puzzling world of murine T regulatory cells

T regulatory cells are essential for downregulation of undesired immune responses and prevention of autoimmune diseases, organ rejection, and graft versus host disease. This review describes the considerable progress made in the recent years in the characterization of the many subsets that constitute the puzzled world of murine T regulatory cells.

Inhibition of pro-inflammatory cytokine generation by CTLA4-Ig in the skin and colon of mice adoptively transplanted with CD45RBhi CD4+ T cells correlates with suppression of psoriasis and colitis

Transfer of CD45RBhi CD4 + naïve T cells into severe combined immunodeficient (SCID) mice induces colitis and skin lesions. Recipients treated with cyclosporin A (CsA), CTLA4-Ig, or vehicle were evaluated for weight loss, skin lesions, and cutaneous blood flow. Necropsy, histological, hematological and cytokine analyses were performed at the conclusion of the experiment to confirm the clinical findings. Vehicle-treated mice lost weight and had 100% incidence of skin lesions by 46-days. CsA-treated mice also lost weight, but only 3/8 mice developed mild, clinically evident skin lesions. In contrast, all CTLA4-Ig-treated mice gained weight and did not develop skin lesions. Increase in cutaneous blood flow correlated with the development of skin lesions. Granulocyte numbers, which were high or moderately high in the vehicle- or CsA-treated mice, respectively, remained as low in the CTLA4-Ig-treated group as in untreated mice. IFN-gamma, IL-1beta, and TNF-alpha levels in the gut and skin correlated with the extent of inflammation in both organs. Histology revealed that CTLA4-Ig but not CsA effectively prevented both autoimmune disorders. The ability of CTLA4-Ig to prevent both colitis and skin lesions suggests that CD28-dependent co-stimulation of T cells is critical for generation of pro-inflammatory cytokines and induction of clinical disease in such autoimmune disorders.

Homeostasis of intestinal immune regulation

Regulatory CD4 T cells with the capacity to inhibit potentially harmful immune responses have been described in various experimental systems. Although the observations are converging towards the naturally activated CD25(+) CD4 T cells as a major population responsible for this protection, there is still considerable disagreement on the molecular and cellular requirements involved to achieve a stable immune homeostasis in vivo.

CTLA-4 upregulation during HIV infection: association with anergy and possible target for therapeutic intervention

OBJECTIVE

To study the role of cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) during HIV infection.

METHODS

Intracellular CTLA-4 expression, determined by flow-cytometry, and proliferative responses to HIV antigens, were studied in peripheral blood mononuclear cells (PBMC) from 93 HIV-1-infected [HIV(+)] patients and 40 HIV-1 seronegative controls.

RESULTS

The proportions of CTLA-4 expressing CD4+ T cells were: (1) significantly higher in HIV(+) patients, 10.95 +/- 0.66%, than in controls, 6 +/- 0.45% (P < 0.0001); (2) inversely correlated to CD4+ counts (r = -0.67, P < 0.005, n = 16, drug-naive patients; r = -0.57, P < 0.0001, n = 77, HAART-treated patients); and (3) positively correlated to proportion of activated (HLA-DR+CD3+) (r = 0.53, P < 0.0001) and memory (CD45RO+CD4+) T cells (r = 0.46, P < 0.001). CD28 median fluorescence intensity in CTLA-4- cells was twice that in CTLA-4+ cells (140 +/- 5.3 versus 70 +/- 2.28, P < 0.00001), whereas cells low in CD28 and CD4, expressed more CTLA-4 (P < 0.0001). Higher proportion of CTLA-4+CD4+ cells expressed CCR5 and Ki-67, in comparison with CTLA-4-CD4+ cells, (65 +/- 11.9 and 25 +/- 7.5% versus 27 +/- 8.9 and 3.7 +/- 2%, P < 0.0001 and P < 0.01, respectively). Among HAART-treated patients, with viral load below detectable levels, CD4+ cells increase was inversely correlated to %CTLA-4+CD4+ cells (r = -0.5, P = 0.003, n = 39). Proliferation of PBMC to anti-CD3, gp-120 depleted HIV-1 antigen or HIV-1 p24 stimulation was inversely correlated with CTLA-4 levels (r = -0.68, P = 0.0035; r = -0.38,P = 0.04; and r = -0.43, P = 0.028, respectively).

CONCLUSIONS

(1) CTLA-4 is upregulated during HIV infection and may therefore account for CD4 T-cell decline and anergy in HIV-1 infection. (2) Increased levels of CTLA-4 may undermine immune responses and in the HAART-treated patient-immune reconstitution. (3) Blocking of CTLA-4 may offer a novel approach for immune-based therapy in HIV infection.

Tolerization of dendritic cells by T(S) cells: the crucial role of inhibitory receptors ILT3 and ILT4

Immunoglobulin-like transcript 3 (ILT3) and ILT4 belong to a family of inhibitory receptors expressed by human monocytes and dendritic cells. We show here that CD8+CD28(-) alloantigen-specific T suppressor (TS) cells induce the up-regulation of ILT3 and ILT4 on monocytes and dendritic cells, rendering these antigen-presenting cells (APCs) tolerogenic. Tolerogenic APCs show reduced expression of costimulatory molecules and induce antigen-specific unresponsiveness in CD4+ T helper cells. Studies of human heart transplant recipients showed that rejection-free patients have circulating TS cells, which induce the up-regulation of ILT3 and ILT4 in donor APCs. These findings demonstrate an important mechanism of immune regulation.