Encephalitogenic CD4 Research Articles

Oligodendrocytes Enforce Immune Tolerance of the Uninfected Brain by Purging the Peripheral Repertoire of Autoreactive CD8+ T Cells

Myelin-specific CD8(+) Tcells are thought to contribute to the pathogenesis of multiple sclerosis. Here we modeled this contribution in mice with CD8(+) Tcells recognizing ovalbumin (OVA) expressed in oligodendrocytes (ODCs). Surprisingly, even very high numbers of activated OVA-reactive CD8(+) Tcells failed to induce disease and were cleared from the immune system after antigen encounter inthe centralnervous system (CNS). Peripheral infection with OVA-expressing Listeria (Lm-OVA) enabled CD8(+) Tcells to enter the CNS, leading to the deletion of OVA-specific clones after OVA recognition on ODCs. In contrast, intracerebral infection allowed OVA-reactive CD8(+) Tcells to cause demyelinating disease. Thus, in response to infection, CD8(+) Tcells also patrol the CNS. If the CNS itself is infected, they destroy ODCs upon cognate antigen recognition in pursuit of pathogen eradication. In the sterile brain, however, antigen recognition on ODCs results in their deletion, thereby maintaining tolerance.

Activation of CD4⁺ Foxp3⁺ regulatory T cells proceeds normally in the absence of B cells during EAE.

B cells and regulatory T (Treg) cells can both facilitate remission from experimental auto immune encephalomyelitis (EAE), a disease of the central nervous system (CNS) used as a model for multiple sclerosis (MS). Considering that B-cell-depletion therapy (BCDT) is used to treat MS patients, we asked whether Treg-cell activation depended on B cells during EAE. Treg-cell proliferation, accumulation in CNS, and augmentation of suppressive activity in the CNS were normal in B-cell-deficient mice, indicating that B cells are not essential for activation of the protective Treg-cell response and thus provide an independent layer of regulation. This function of B cells involved early suppression of the encephalitogenic CD4(+) T-cell response, which was enhanced in B-cell-deficient mice. CD4(+) T-cell depletion was sufficient to intercept the transition from acute-to-chronic EAE when applied to B-cell-deficient animals that just reached the peak of disease severity. Intriguingly, this treatment did not improve disease when applied later, implying that chronic disability was ultimately maintained independently of pathogenic CD4(+) T cells. Collectively, our data indicate that BCDT is unlikely to impair Treg-cell function, yet it might produce undesirable effects on T-cell-mediated autoimmune pathogenesis.

MCAM Identifies Encephalitogenic TH17 Lymphocytes and Promotes Their Recruitment to the CNS (SC02.001)

Objective: Our hypothesis is that MCAM plays an important role in CNS inflammation by promoting migration of aggressive autoreactive lymphocytes through the BBB into the CNS parenchyma. Background In multiple sclerosis (MS), encephalitogenic CD4 + lymphocytes require adhesion molecules to accumulate into central nervous system (CNS) lesions. Blocking of alpha4beta1 integrin reduces relapses but serious adverse events can arise because of the resulting CNS immunosuppression. Thus, we need to identify new molecules specifically involved in the recruitment through the BBB of highly inflammatory immune cell populations such as T H 17 lymphocytes. We identified expression of melanoma cell adhesion molecule (MCAM), a molecule that can interact with itself, on a subset of human effector memory CD4+ lymphocytes and on blood-brain barrier (BBB) endothelium. Design/Methods: Combination of ex vivo, in vitro and in situ studies using human and mouse material from healthy controls and from MS subjects and from the MS mouse model Experimental Autoimmune Encephalomyelitis (EAE). In vivo studies in EAE. Results: We demonstrate that MCAM is co-expressed by RORgamma + and IL-23Receptor + memory CD4 + lymphocytes, and that MCAM + lymphocytes express more IL-17, IL-22, GM-CSF and Granzyme B than MCAM neg lymphocytes. The proportion of MCAM + CD4 + lymphocytes is higher in the blood and in the CNS of patients affected by MS and in EAE animals, as compared to controls, and MCAM is strikingly up-regulated at the level of the BBB within lesions. Furthermore, MCAM + T H 17 lymphocytes migrate more efficiently than MCAM neg cells and MCAM blockade reduces T H 17 lymphocyte adhesion and transmigration across BBB-ECs in vitro. In vivo , MCAM depletion dampens the clinical and pathological severity of EAE and the infiltration of IL-17 + lymphocytes in the CNS of EAE animals. Conclusions: Our findings indicate that MCAM could serve as a biomarker for T H 17-dependent diseases and represents a valuable target for the treatment of T H 17-dependent CNS inflammation. Supported by: The MSSociety of Canada and the CIHR. Disclosure: Dr. Larochelle has nothing to disclose. Dr. Cayrol has nothing to disclose. Dr. Kebir has nothing to disclose. Dr. Lecuyer has nothing to disclose. Dr. Alvarez has nothing to disclose. Dr. Arbour has nothing to disclose. Dr. Prat has nothing to disclose.

Two discreet subsets of CD8 T cells modulate PLP91–110 induced experimental autoimmune encephalomyelitis in HLA-DR3 transgenic mice

Previously we showed that transgenic mice expressing human HLA-DR3 gene are susceptible to PLP91–110 induced experimental autoimmune encephalomyelitis (EAE) and can serve as an animal model of multiple sclerosis (MS). HLA-DR3 mice with EAE showed increased number of CD8 T cells indicating their important role in disease pathogenesis. The role of CD8 T cells in MS, an inflammatory demyelinating disease of CNS, has been enigmatic as it has been assigned both regulatory and pathogenic roles. Therefore, to evaluate the role of CD8 T cells, we generated CD8 deficient HLA-DR3 transgenic mice (DR3.CD8−/−). Immunization with PLP91–110 led to more severe EAE in DR3.CD8−/− mice compared to HLA-DR3 mice indicating a regulatory role for CD8 T cells. Interestingly, DR3.CD8−/− mice with EAE showed decreased CNS pathology compared to DR3 mice thus suggesting a pathogenic role for CD8 T cells. We show that these two subsets of CD8 T cells can be differentiated based on the surface expression of CD122 (IL-2 Rβ chain). CD8 T cells expressing CD122 (CD8+CD122+) play a regulatory role while CD8+CD122− T cells act as a pathogenic subset. CD122 expressing CD8 T cells are the regulatory subset of CD8 T cells and regulate the encephalitogenic CD4 T cells through direct modulation of antigen presenting cells and/or through the release of immunoregulatory cytokines such as IL-10, IFNγ and TGFβ. We also showed that adoptive transfer of CD8CD122− T cells caused increased spinal cord demyelination indicating that these are pathogenic subset of CD8 T cells. Our study suggests that CD8+ T cells play both regulatory as well as pathogenic role in disease pathogenesis of EAE. A better understanding of these subsets could aid in designing novel therapy for MS patients.

Nogo-Receptors NgR1 and NgR2 Do Not Mediate Regulation of CD4 T Helper Responses and CNS Repair in Experimental Autoimmune Encephalomyelitis

Myelin-associated inhibition of axonal regrowth after injury is considered one important factor that contributes to regeneration failure in the adult central nervous system (CNS). Blocking strategies targeting this pathway have been successfully applied in several nerve injury models, including experimental autoimmune encephalomyelitis (EAE), suggesting myelin-associated inhibitors (MAIs) and functionally related molecules as targets to enhance regeneration in multiple sclerosis. NgR1 and NgR2 were identified as interaction partners for the myelin proteins Nogo-A, MAG and OMgp and are probably mediating their growth-inhibitory effects on axons, although the in vivo relevance of this pathway is currently under debate. Recently, alternative functions of MAIs and NgRs in the regulation of immune cell migration and T cell differentiation have been described. Whether and to what extent NgR1 and NgR2 are contributing to Nogo and MAG-related inhibition of neuroregeneration or immunomodulation during EAE is currently unknown. Here we show that genetic deletion of both receptors does not promote functional recovery during EAE and that NgR1 and NgR2-mediated signals play a minor role in the development of CNS inflammation. Induction of EAE in Ngr1/2-double mutant mice resulted in indifferent disease course and tissue damage when compared to WT controls. Further, the development of encephalitogenic CD4+ Th1 and Th17 responses was unchanged. However, we observed a slightly increased leukocyte infiltration into the CNS in the absence of NgR1 and NgR2, indicating that NgRs might be involved in the regulation of immune cell migration in the CNS. Our study demonstrates the urgent need for a more detailed knowledge on the multifunctional roles of ligands and receptors involved in CNS regeneration failure.

Lymph node-derived donor encephalitogenic CD4+T cells in C57BL/6 mice adoptive transfer experimental autoimmune encephalomyelitis highly express GM-CSF and T-bet

Experimental autoimmune encephalomyelitis (EAE) is a relevant animal model for the human demyelinating inflammatory disorder of the central nervous system (CNS), multiple sclerosis (MS). Induction of EAE by adoptive transfer allows studying the role of the donor T lymphocyte in disease pathogenesis. It has been challenging to reliably induce adoptive transfer EAE in C57BL/6 (H-2b) mice. The goal of this study was to develop a reproducible and high yield protocol for adoptive transfer EAE in C57BL/6 mice. A step-wise experimental approach permitted us to develop a protocol that resulted in a consistent relatively high disease incidence of ~70% in recipient mice. Donor mice were immunized with myelin oligodendrocyte glycoprotein (MOG)p35-55 in complete Freund's adjuvant (CFA) followed by pertussis toxin (PT). Only lymph node cells (LNC) isolated at day 12 post immunization, and restimulated in vitro for 72 hours with 10 μg/mL of MOGp35-55 and 0.5 ng/mL of interleukin-12 (IL-12) were able to transfer disease. The ability of LNC to transfer disease was associated with the presence of inflammatory infiltrates in the CNS at day 12. Interferon gamma (IFNγ) was produced at comparable levels in cell cultures prepared from mice at both day 6 and day 12 post immunization. By contrast, there was a trend towards a negative association between IL-17 and disease susceptibility in our EAE model. The amount of GM-CSF secreted was significantly increased in the culture supernatants from cells collected at day 12 post immunization versus those collected at day 6 post-immunization. Activated CD4+ T cells present in the day 12 LNC cultures maintained expression of the transcription factor T-bet, which has been shown to regulate the expression of the IL-23 receptor. Also, there was an increased prevalence of MOGp35-55-specific CD4+ T cells in day 12 LNC after in vitro re-stimulation. In summary, encephalitogenic LNC that adoptively transfer EAE in C57BL/6 mice were not characterized by a single biomarker in our study, but by a composite of inflammatory markers. Our data further suggest that GM-CSF expression by CD4+ T cells regulated by IL-23 contributes to their encephalitogenicity in our EAE model.

Endogenous estrogens, through estrogen receptor α, constrain autoimmune inflammation in female mice by limiting CD4+ T‐cell homing into the CNS

Sex hormones influence immune responses and the development of autoimmune diseases including MS and its animal model, EAE. Although it has been previously reported that ovariectomy could worsen EAE, the mechanisms implicated in the protective action of endogenous ovarian hormones have not been addressed. In this report, we now show that endogenous estrogens limit EAE development and CNS inflammation in adult female mice through estrogen receptor α expression in the host non-hematopoietic tissues. We provide evidence that the enhancing effect of gonadectomy on EAE development was due to quantitative rather than qualitative changes in effector Th1 or Th17 cell recruitment into the CNS. Consistent with this observation, adoptive transfer of myelin oligodendrocyte glycoprotein-specific encephalitogenic CD4(+) T lymphocytes induced more severe EAE in ovariectomized mice as compared to normal female mice. Finally, we show that gonadectomy accelerated the early recruitment of inflammatory cells into the CNS upon adoptive transfer of encephalitogenic CD4(+) T cells. Altogether, these data show that endogenous estrogens, through estrogen receptor α, exert a protective effect on EAE by limiting the recruitment of blood-derived inflammatory cells into the CNS.

MHC class II–restricted antigen presentation by plasmacytoid dendritic cells inhibits T cell–mediated autoimmunity

Although plasmacytoid dendritic cells (pDCs) express major histocompatibility complex class II (MHCII) molecules, and can capture, process, and present antigens (Ags), direct demonstrations that they function as professional Ag-presenting cells (APCs) in vivo during ongoing immune responses remain lacking. We demonstrate that mice exhibiting a selective abrogation of MHCII expression by pDCs develop exacerbated experimental autoimmune encephalomyelitis (EAE) as a consequence of enhanced priming of encephalitogenic CD4+ T cell responses in secondary lymphoid tissues. After EAE induction, pDCs are recruited to lymph nodes and establish MHCII-dependent myelin-Ag–specific contacts with CD4+ T cells. These interactions promote the selective expansion of myelin-Ag–specific natural regulatory T cells that dampen the autoimmune T cell response. pDCs thus function as APCs during the course of EAE and confer a natural protection against autoimmune disease development that is mediated directly by their ability to present of Ags to CD4+ T cells in vivo.

Antigen-Specific CD25 −Foxp3 −IFN-γ highCD4 + T Cells Restrain the Development of Experimental Allergic Encephalomyelitis by Suppressing Th17

The current study identifies within the Th1 subtype two distinct CD4(+) populations: those capable of transferring inflammatory autoimmunity and others that regulate its development by suppressing Th17 in an interferon (IFN)-gamma-dependent manner. These CD4(+)IFN-gamma(high)IL-4(low)IL-10(low)TGF-beta(low)FOXp3(-) cells in fact function as antigen-specific regulatory cells that restrain the development of autoimmunity by increasing the threshold of Th17 activation. We show that development of autoimmune conditions within the central nervous system is dependent on the Fas ligand-mediated apoptosis of these regulatory cells at early stages of disease. We also show that not only is the function of these cells IFN-gamma dependent but also that stable over expression of IFN-gamma in encephalitogenic CD4(+) T cells redirects their biological function to become antigen-specific regulatory cells. This may also explain, in part, the pleiotropic role of IFN-gamma in the regulation of autoimmunity, as previously observed by others.

Fingolimod (FTY720) ameliorates experimental autoimmune encephalomyelitis (EAE): II. FTY720 decreases infiltration of Th17 and Th1 cells into the central nervous system in EAE

Fingolimod (FTY720), a sphingosine 1-phosphate (S1P) receptor modulator, is highly effective in experimental autoimmune encephalomyelitis (EAE) and decreases circulating mature lymphocytes by inhibiting S1P-dependent lymphocyte egress from secondary lymphoid organs. Infiltration of encephalitogenic CD4 T cells plays a critical role in the development and progression of EAE in mice. In this study, we investigated the effects of FTY720 on infiltration of interleukin 17 (IL-17)-expressing helper T cells (Th17 cells) and interferon-γ-expressing type 1 helper T cells (Th1 cells) into the spinal cords in EAE mice induced by immunization with myelin oligodendrocyte glycoprotein (MOG). Prophylactic treatment with FTY720 at an oral dose of 0.3 mg/kg significantly inhibited the development of EAE and markedly reduced the frequency of Th17 and Th1 cells in the spinal cords of EAE mice. On the contrary, the frequency of Th17 and Th1 cells in draining inguinal lymph nodes was increased to approximately 2-fold by FTY720, suggesting sequestration of myelin antigen-specific Th cells into draining lymph nodes. Moreover, we found that Th17 and Th1 cells could migrate toward 10 nM S1P and that the pretreatment with 1 nM FTY720-phosphate, an active metabolite of FTY720, almost completely inhibited S1P-induced migration of these Th cells. On the other hand, FTY720-phosphate up to 100 nM showed no clear effect on generation of these Th cells or cytokine production by them. From these results, the ameliorating effects of FTY720 on EAE are likely due to reduction of infiltration of encephalitogenic Th17 and Th1 cells into the central nervous system.

Fingolimod (FTY720) ameliorates experimental autoimmune encephalomyelitis (EAE): I. Oral administration of FTY720 effectively inhibits relapse of EAE

Experimental autoimmune encephalomyelitis (EAE) is a CD4 T cell-mediated disease model for multiple sclerosis (MS). When SJL/J mice are immunized with myelin proteolipid protein (PLP), EAE symptoms were developed within 2 weeks, remitted thereafter, and then relapsed at about 3 weeks after immunization, indicating that EAE induced by PLP in SJL/J mice shares a certain characteristic with relapsing remitting MS. In this study, we evaluated the preventing effect of fingolimod (FTY720), a sphingosine 1-phosphate receptor modulator, on relapse of EAE induced by PLP in SJL/J mice. When FTY720 at oral does of 0.1 and 0.3 mg/kg was administered daily after establishment of EAE, relapse of EAE was markedly inhibited during administration period. The relapse of EAE was significantly inhibited by subcutaneous administration of recombinant mouse interferon-β (rm-IFN-β) at 10000 IU every other day at early period; however EAE was relapsed in the half number of mice in latter period. These results indicate that FTY720 shows a more marked preventing effect on relapse of EAE compared with rm-IFN-β. By immunohistochemical staining, it is revealed that the area of demyelination and the infiltration of CD4 T cells are significantly reduced in the spinal cords of EAE mice by FTY720. Interestingly, FTY720 markedly decreased infiltration of PLP-specific, interleukin 17-expressing CD4 T cells (Th17 cells) into the spinal cords. Consequently, the preventing effect of FTY720 on relapse of EAE is likely due to reduction of infiltration of encephalitogenic CD4 T cells into the central nervous system.

Manipulating Antigenic Ligand Strength to Selectively Target Myelin-Reactive CD4+ T Cells in EAE

The development of antigen-specific therapies for the selective tolerization of autoreactive T cells remains the Holy Grail for the treatment of T-cell-mediated autoimmune diseases such as multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). This quest remains elusive, however, as the numerous antigen-specific strategies targeting myelin-specific T cells over the years have failed to result in clinical success. In this review, we revisit the antigen-based therapies used in the treatment of myelin-specific CD4+ T cells in the context of the functional avidity and the strength of signal of the encephalitogenic CD4+ T cell repertoire. In light of differences in activation thresholds, we propose that autoreactive T cells are not all equal, and therefore tolerance induction strategies must incorporate ligand strength in order to be successful in treating EAE and ultimately the human disease MS.

Encephalitogenic T cells that stably express both T-bet and ROR γt consistently produce IFN γ but have a spectrum of IL-17 profiles

Th1/Th17 cells, secreting both IFN γ and IL-17, are often associated with inflammatory pathology. We cloned and studied the cytokine phenotypes of MBP-specific, TCR-identical encephalitogenic CD4+ cells in relationship to Th1- and Th17-associated transcription factors T-bet and ROR γt. IFN γ-producing cells could be sub-divided into those that are T-bet +/ROR γt − and those that are T-bet +/ROR γt +. The latter comprises a spectrum of phenotypes, as defined by IL-17 production, and can be induced to up-regulate IL-23R with IL-12 or IL-23. The former, bona fide Th1 cells, lack IL-23R expression under all conditions. In vivo, T-bet +/ROR γt − and T-bet +/ROR γt + clones induce EAE equally well.

T‐cell seeding: neonatal transfer of anti‐myelin basic protein T‐cell lines renders Fischer rats susceptible later in life to the active induction of experimental autoimmune encephalitis

Fischer strain rats resist active induction of experimental autoimmune encephalomyelitis (EAE) following immunization with guinea-pig myelin basic protein (MBP) in complete Freund's adjuvant (CFA). Nevertheless, we now report that an encephalitogenic CD4(+) anti-MBP T-cell line could be developed from actively immunized Fischer rats. Adoptive transfer of the activated line mediated acute EAE in adult Fischer rats, but not in 1-day-old rats. Moreover, we found that both resting and activated anti-MBP T cells injected 1 day post-natally rendered these rats susceptible later in life to the active induction of EAE by immunization with MBP/CFA. The actively induced EAE manifested the accelerated onset of a secondary, memory-type response. Resting anti-MBP T cells injected even up to 2 weeks post-natally produced no clinical signs but seeded 50-100% of the recipients for an active encephalitogenic immune response to MBP. An earlier T-cell injection (1-2 days) produced a higher incidence and stronger response. The transferred resting T cells entered the neonatal spleen and thymus and proliferated there but did not change the total anti-MBP precursor number in adults. Splenocytes harvested from rats that were injected neonatally but not exposed to MBP in vivo proliferated strongly and produced significant amounts of interferon-gamma to MBP in vitro. Similar results were observed in rats injected with resting T-cell lines reactive to ovalbumin, suggesting that the neonatal injection of resting T cells specific for a self or for a foreign antigen can seed the immune system with the potential for an enhanced effector response to that antigen later in life.

IFNbeta inhibits DC migration in vitro and in vivo (92.2)

Abstract Interferon β (IFN β) is a widely approved therapeutic option for the treatment of multiple sclerosis (MS)/experimental autoimmune encephalomyelitis (EAE). However, the molecular mechanisms underlying the effects of IFNβ in MS/EAE are still not fully understood. In EAE, the major players are encephalitogenic CD4+ T cells and perivascular myeloid dendritic cells (DC). Therefore, migration of both peripheral T cells and DC into the CNS is essential for development of EAE/MS. Migration of DC from the inflammatory site to draining lymph nodes for antigen presentation and activation of naïve T cells, and to the CNS during chronic neuroinflammation requires CCR7 and MMP-9 expression. In this study, we report for the first time that IFNβ inhibits CCR7 expression and MMP-9 production in DC matured with a cytokine cocktail (TNFα+IL-1+IL-6+PGE2). In addition, DC matured in the presence of IFNβ exhibit a lower migratory capacity compared to mature DC. STAT-1 signaling is essential for IFNβ-mediated inhibition of CCR7 and MMP-9 expression, and subsequent DC migration. Our in vivo data also show that mice treated with IFNβ have a lower number of DC migrating to the draining lymph nodes following exposure to FITC as compared to controls. In conclusion, our results provide an addition mechanism for the beneficial effect of IFNβ in MS/EAE through the inhibition of mature DC migration. This work is support by NIH 2RO1AI052306

The Th17–ELR+ CXC chemokine pathway is essential for the development of central nervous system autoimmune disease

The ELR+ CXC chemokines CXCL1 and CXCL2 are up-regulated in the central nervous system (CNS) during multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). However, their functional significance and the pathways regulating their expression are largely unknown. We show that transfer of encephalitogenic CD4+ Th17 cells is sufficient to induce CXCL1 and CXCL2 transcription in the spinal cords of naive, syngeneic recipients. Blockade or genetic silencing of CXCR2, a major receptor for these chemokines in mice, abrogates blood–brain barrier (BBB) breakdown, CNS infiltration by leukocytes, and the development of clinical deficits during the presentation as well as relapses of EAE. Depletion of circulating polymorphonuclear leukocytes (PMN) had a similar therapeutic effect. Furthermore, injection of CXCR2+ PMN into CXCR2−/− mice was sufficient to restore susceptibility to EAE. Our findings reveal that a Th17–ELR+ CXC chemokine pathway is critical for granulocyte mobilization, BBB compromise, and the clinical manifestation of autoimmune demyelination in myelin peptide–sensitized mice, and suggest new therapeutic targets for diseases such as MS.

Dendritic cells permit immune invasion of the CNS in an animal model of multiple sclerosis

Immunization with myelin antigens leads to the development of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. The disease can also be induced by the transfer of encephalitogenic CD4+ T helper (T(H)) lymphocytes into naive mice. These T cells need to re-encounter their cognate antigen in the context of major histocompatibility complex (MHC) class II-bearing antigen-presenting cells (APCs) in order to recognize their target. The cell type and location of the APC mediating T-cell entry into the central nervous system (CNS) remain unknown. Here, we show that APCs of the lymphoreticular system and of the CNS parenchyma are dispensable for the immune invasion of the CNS. We also describe that a discrete population of vessel-associated dendritic cells (DCs) is present in human brain tissue. In mice, CD11c+ DCs alone are sufficient to present antigen in vivo to primed myelin-reactive T cells in order to mediate CNS inflammation and clinical disease development.

Infection-induced apoptosis deletes bystander CD4 + T cells: a mechanism for suppression of autoimmunity during BCG infection

Infection with Mycobacterium bovis Bacille Calmette Guérin (BCG) induces high levels of apoptosis among activated CD4 + T cells. We have investigated the specificity of this pro-apoptotic response and its influence on CD4 + T cell mediated autoimmunity. Apoptosis induced by BCG-infection is unrelated to antigenic specificity, as demonstrated by the increased apoptosis of activated TCR transgenic CD4 + T cells of unrelated specificity. Moreover, infection-induced apoptosis promoted the deletion of CD4 + T cells activated either by peptide or anti-CD3/anti-CD28 stimulation. Infection-induced apoptosis required IFN-γ production by the infected host, and expression of the IFN-γ receptor on donor CD4 + T cells. We used an adoptive transfer model of experimental autoimmune encephalomyelitis (EAE) to assess the influence of infection-induced apoptosis on a CD4 + T cell-mediated response. A significantly higher level of apoptosis was seen among sorted encephalitogenic CD4 + T cells transferred to BCG-infected versus uninfected hosts. BCG-infected mice displayed a milder course of clinical disease than their uninfected counterparts and a decreased recovery of donor cells from the CNS. The data suggest that mycobacterial infection attenuates the severity of EAE, at least in part, by promoting the apoptotic elimination of autoreactive CD4 + T cells.

Suppression of CD4 + T cell activation by a novel inhibitor of Src family kinases

The Src family kinases Lck and Fyn play an important role in T cell development and function. We have synthesized a novel small molecule, A-420983, which inhibits Lck and Fyn, as well as other Src family kinases, but has selectivity with respect to non-Src family kinases. A-420983 completely inhibited antigen-stimulated production of IFN-γ and IL-4 by mouse Th1 and Th2 cells, respectively. Antigen-induced T cell proliferation was also blocked by treatment with A-420983. In contrast, IL-15-induced proliferation was unaffected by A-420983, suggesting that TCR-independent pathways of T cell activation were not impaired. When mice were dosed orally, A-420983 inhibited TCR-mediated c-jun and ZAP-70 phosphorylation in CD4 + T cells and suppressed the disease course of established EAE. Treatment with A-420983 for 7 days resulted in a block in thymocyte development at the CD4 − CD8 − stage, consistent with inhibition of Lck and Fyn in vivo. These results demonstrate that a small molecule inhibitor of Lck and Fyn can block TCR-induced T cell activation in vitro and in vivo. Furthermore, CNS demyelination mediated by activated encephalitogenic CD4 + T cells is dependent upon the kinase activity of these Src family members. We conclude that inhibition of Src family kinases may represent a promising strategy for the treatment of T cell-mediated disorders.

Recombinant TCR ligand induces early TCR signaling and a unique pattern of downstream activation.

Recombinant TCR ligands (RTLs) consisting of covalently linked alpha(1) and beta(1) domains of MHC class II molecules tethered to specific antigenic peptides represent minimal TCR ligands. In a previous study we reported that the rat RTL201 construct, containing RT1.B MHC class II domains covalently coupled to the encephalitogenic guinea pig myelin basic protein (Gp-MBP(72-89)) peptide, could prevent and treat actively and passively induced experimental autoimmune encephalomyelitis in vivo by selectively inhibiting Gp-MBP(72-89) peptide-specific CD4(+) T cells. To evaluate the inhibitory signaling pathway, we tested the effects of immobilized RTL201 on T cell activation of the Gp-MBP(72-89)-specific A1 T cell hybridoma. Activation was exquisitely Ag-specific and could not be induced by RTL200 containing the rat MBP(72-89) peptide that differed by a threonine for serine substitution at position 80. Partial activation by RTL201 included a CD3zeta p23/p21 ratio shift, ZAP-70 phosphorylation, calcium mobilization, NFAT activation, and transient IL-2 production. In comparison, anti-CD3epsilon treatment produced stronger activation of these cellular events with additional activation of NF-kappaB and extracellular signal-regulated kinases as well as long term increased IL-2 production. These results demonstrate that RTLs can bind directly to the TCR and modify T cell behavior through a partial activation mechanism, triggering specific downstream signaling events that deplete intracellular calcium stores without fully activating T cells. The resulting Ag-specific activation of the transcription factor NFAT uncoupled from the activation of NF-kappaB or extracellular signal-regulated kinases constitutes a unique downstream activation pattern that accounts for the inhibitory effects of RTL on encephalitogenic CD4(+) T cells.