Analysis of TCR V beta gene usage and encephalitogenicity of myelin basic protein peptide p91-103 reactive T cell clones in SJL mice: lack of evidence for V gene hypothesis

Anatomy of T cell autoimmunity to myelin oligodendrocyte glycoprotein (MOG): Prime role of MOG44F in selection and control of MOG-reactive T cells in H-2b mice

Myelin oligodendrocyte glycoprotein (MOG) is an important myelin target antigen, and MOG-induced EAE is now a widely used model for multiple sclerosis. Clonal dissection revealed that MOG-induced EAE in H-2(b) mice is associated with activation of an unexpectedly large number of T cell clones reactive against the encephalitogenic epitope MOG35-55. These clones expressed extremely diverse TCR with no obvious CDR3alpha/CDR3beta motif(s). Despite extensive TCR diversity, the cells required MOG40-48 as their common core epitope and shared MOG44F as their major TCR contact. Fine epitope-specificity analysis with progressively truncated peptides suggested that the extensive TCR heterogeneity is mostly related to differential recognition of multiple overlapping epitopes nested within MOG37-52, each comprised of a MOG40-48 core flanked at the N- and/or the C-terminus by a variable number of residues important for interaction with different TCR. Abrogation of both the encephalitogenic potential of MOG and T cell reactivity against MOG by a single mutation (MOG44F/MOG44A), together with effective down-regulation of MOG-induced EAE by MOG37-44A-52, confirmed in vivo the primary role for MOG44F in the selection/activation of MOG-reactive T cells. We suggest that such a highly focused T cell autoreactivity could be a selective force that offsets the extensive TCR diversity to facilitate a more "centralized control" of pathogenic MOG-related T cell autoimmunity.

Inhibition of CD40 signaling pathway by tyrphostin A1 reduces secretion of IL-12 in macrophage, Th1 cell development and experimental allergic encephalomyelitis in SJL/J mice

Activation of antigen presenting cells through the interaction of CD40 with its ligand is a critical co-stimulatory signal for IL-12 production and Th1 differentiation. Tyrphostins are organic molecules that inhibit the phosphorylation of protein tyrosine kinases. We show that tyrphostin A1 inhibits CD40L-stimulated IL-12 production in macrophage cultures and antigen-induced generation of Th1 cells. Our data also show that tyrphostin A1 blocks CD40L-induced translocation of NF-kappaB to the nucleus, and reduces the activation of IL-12 p40 gene. In vivo therapy with A1 leads to decrease in generation of myelin basic protein (MBP) specific encephalitogenic T cells. In addition, treatment of SJL/J mice with A1 results in attenuation of experimental allergic encephalomyelitis (EAE).

Effect of staphylococcal enterotoxin B injection on the development of experimental autoimmune encephalomyelitis: influence of cytokine and inducible nitric oxide synthase production

Possible mechanisms involved in the protective effect of staphylococcal enterotoxin B (SEB) injection on the subsequent development of experimental autoimmune encephalomyelitis (EAE) were investigated. Only partial clonal deletion and anergy of Vbeta8 + T-lymphocytes were documented after myelin basic protein immunization in SEB injected mice. Brain permeability was not influenced. Within the brain or during in vitro rechallenge assays SEB protected mice produced significantly more IL-10, IL-4, TNF-alpha and iNOS. It is suggested that the immune deviating effect of SEB may be involved in its EAE protective effect.

Tyrphostin B42 Inhibits IL-12-Induced Tyrosine Phosphorylation and Activation of Janus Kinase-2 and Prevents Experimental Allergic Encephalomyelitis

IL-12 is a macrophage-derived cytokine that induces proliferation, cytokine production, and cytotoxic activity of T and NK cells. Signaling through its receptor, IL-12 induces these cellular responses by tyrosine phosphorylation and activation of Janus kinase-2 (Jak-2), Tyk-2, Stat3, and Stat4. We have used tyrphostin B42 (AG490), a Jak-2 inhibitor, to determine the role of Jak-2 kinase in IL-12 signaling and IL-12-induced T cell functions. Treatment of activated T cells with tyrphostin B42 inhibited the IL-12-induced tyrosine phosphorylation and activation of Jak-2 without affecting Tyk-2 kinase. In contrast, treatment with tyrphostin A1 inhibited the tyrosine phosphorylation of Tyk-2 but not that of Jak-2 kinase. Inhibition of either Jak-2 or Tyk-2 leads to a decrease in the IL-12-induced tyrosine phosphorylation of Stat3, but not of Stat4, protein. While inhibition of Jak-2 lead to programmed cell death, the inhibition of Jak-2 or Tyk-2 resulted a decrease in IFN-γ production. We have further tested the in vivo effects of tyrphostin B42 in experimental allergic encephalomyelitis, a Th1 cell-mediated autoimmune disease. In vivo treatment with tyrphostin B42 decreased the proliferation and IFN-γ production of neural Ag-specific T cells. Treatment of mice with tyrphostin B42 also reduced the incidence and severity of active and passive EAE. These results suggest that tyrphostin B42 prevents EAE by inhibiting IL-12 signaling and IL-12-mediated Th1 differentiation in vivo.

TGF-β Inhibits IL-12-Induced Activation of Jak-STAT Pathway in T Lymphocytes

IL-12 is a macrophage-derived heterodimeric cytokine, capable of inducing proliferation, cytokine production, and cytotoxic activity of NK cells and T cells, and is critical for the development of Th1 responses. TGF-β is an immunosuppressive cytokine that inhibits IL-12-mediated responses in NK and T cells. To determine the mechanism of action of TGF-β, we examined its inhibitory effect on IL-12 signal-transduction pathway in T cells. Stimulation of activated T cells with IL-12 leads to tyrosine phosphorylation and activation of Jak-2 and Tyk-2 kinases and STAT3 and STAT4 transcription factors. Treatment of activated T cells with TGF-β blocked IL-12-induced tyrosine phosphorylation and activation of both Jak-2 and Tyk-2 kinases. Furthermore, inhibition of Jak kinases by TGF-β was associated with a decrease in tyrosine phosphorylation of STAT3 and STAT4 proteins. Abrogation of IL-12-induced Jak-Stat pathway by TGF-β resulted in decreased T cell proliferation and IFN-γ production, and increased apoptotic cell death. These findings highlight that TGF-β inhibits IL-12-mediated responses by blocking IL-12 signal transduction in T cells.

Induction of a heterogeneous TCR repertoire in (PL/JXSJL/J)F1 mice by myelin basic protein peptide Ac1-11 and its analog Ac1-11[4A]

Experimental autoimmune encephalomyelitis (EAE) serves as a rodent model of the autoimmune disease multiple sclerosis. In mice, EAE is induced by immunizing with spinal cord homogenate, components of the myelin sheath, such as myelin basic protein (MBP) or proteolipid protein (PLP), or peptides derived from these components. EAE can be induced in H-2u or (H-2u x H-2s)F1 mice with the N-terminal peptide of MBP, Ac1-11. Coimmunization with Ac1-11 and Ac1-11[4A], an analog in which lysine at position four is substituted with alanine, prevents EAE. The mechanism of inhibition has not been elucidated, but probably does not work through MHC blockade, T cell anergy or clonal elimination of encephalitogenic T cells. We have isolated T cell clones and hybridomas from (PL/J x SJL/J)F1 mice immunized with either Ac1-11 alone or Ac1-11 and Ac1-11[4A] and analysed these cells for differences in their T cell receptor repertoire and in vitro response. Although T cells elicited by coinjection of Ac1-11 and Ac1-11[4A] expressed TCR that used V alpha and Vbeta gene elements similar to those elicited by Ac1-11 alone, they differed in the sequences of the junctional region of the alpha chain. Most of these T cells also responded less well to Ac1-11 in vitro, suggesting that coinjection of Ac1-11 and Ac1-11[4A] preferentially activates T cells bearing TCR of different affinity for Ac1-11 bound to I-A(u), and which may therefore be less encephalitogenic. Furthermore, our results show that a more diverse repertoire of V alpha and Vbeta genes are elicited by Ac1-11 in (PL/J x SJL/J)F1 mice compared to PL/J and B10.PL mice, providing further evidence that a restricted TCR repertoire is not required for the development of autoimmune disease.

Recruitment of multiple V beta genes in the TCR repertoire against a single pathogenic thyroglobulin epitope

In autoimmune thyroid disease, the question whether thyroid-infiltrating, autoreactive T cells are derived from a polyclonal or oligoclonal subset has been the subject of considerable debate. In this report, we have examined the T-cell receptor (TCR) V beta profile of mouse clonal T cells responding to a single thyroiditogenic epitope, the As-restricted, 9mer mouse thyroglobulin (MTg) peptide (2496-04). In vitro recall assays based on lymph node cell (LNC) proliferation and cytokine release demonstrated that this peptide is a minimal T-cell epitope inducing a T-helper 1 (Th1) type of response in SJL hosts. A panel of cloned, interleukin-2 (IL-2)-secreting hybridomas was generated from this Th1 subset and their TCR-V beta gene utilization was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Ten clones derived from two independent fusions were found to utilize three V beta gene families (V beta 2, 4, and 17). To the extent that Tg or other thyroid autoantigens encompass multiple pathogenic epitopes it appears unlikely from these data that a restricted TCR-V beta chain usage will be a general characteristic of thyroiditogenic T cells.

Differential expression of protein tyrosine kinases and their phosphorylation in murine Th1 cells anergized with class II MHC-peptide complexes

In resting T cell clones, antigen presentation with immobilized anti-CD3 or anti-T cell receptor (TCR) is known to result in a state of anergy as characterized by unresponsiveness to normal antigenic restimulation. Similarly, T cell unresponsiveness could be induced by immobilized (plate-coated) complexes of purified class II MHC and antigenic peptide. It is not clearly defined whether the engagement of TCR by immobilized anti-TCR or immobilized class II MHC-peptide complexes generates similar or differential signals during the induction of T cell unresponsiveness. In order to address the initial signalling events induced by TCR occupancy with anti-TCR and class II MHC-peptide molecules, the expression of three critical protein tyrosine kinases (PTK) and their phosphorylation were investigated in the present study using a murine T cell clone (HS17) restricted for IAS and myelin basic protein (MBP (91-103)) peptide. The anergic T cells induced by immobilized IAS-MBP (91-103) complex or anti-TCR (H57) showed differential expression of lck (56 kDa) and Zap-70 (70 kDa) proteins. In both systems, however, the induction of T cell unresponsiveness was accompanied by increased level of fyn (59 kDa) expression. When analysed for the total tyrosine phosphorylation of PTK, anergic HS17 T cells induced by both molecules showed increased phosphorylation associated with only the fyn protein. These results suggest that the signal transduction events induced by immobilized class II MHC-peptide complexes and anti-TCR are distinct, although both can initiate signals that lead to increased fyn expression and phosphorylation. In addition, the present study supports the evidence for the important functional association of fyn protein with direct TCR engagement in T cell signalling.

Modulation of experimental allergic encephalomyelitis in mice by immunization with a peptide specific for the gamma delta T cell receptor

This study investigated the role of gamma delta T cells in experimental allergic encephalomyelitis (EAE), a chronic inflammatory disease of the central nervous system (CNS) that resembles multiple sclerosis. The strategy was to assess the effect on EAE of TCR peptide immunization directed against V gamma 6 T cells, shown recently to predominate in the CNS of mice during the early stages of EAE. The data show that TCR peptide immunization specific for V gamma 6 chains does not induce protection against EAE, since the incidence of EAE in TCR treated animals was similar to control mice, and therefore does not affect disease susceptibility per se, but rather alters the development of the disease. Specifically, there was a delay in the onset of EAE and a reduction in disease severity in TCR treated animals, although the effects were not highly significant. These findings suggest a role for gamma delta T cells in the development of EAE; however, further studies are necessary to confirm the specificity of TCR peptide immunization.

Heterogeneous T cell receptor V beta gene repertoire in murine interstitial nephritis

Anti-tubular basement membrane disease (alpha TBM) produces T cell-mediated interstitial nephritis in SJL/J mice following immunization with heterologous renal tubular antigen. Initial mononuclear infiltrates appear in vivo after six to eight weeks, with subsequent progression to renal fibrosis and endstage kidney disease. Cultured lymph node derived nephritogenic T cells from these mice react to a small epitopic region of the 3M-1 target antigen and share a common amino acid motif in their V beta CDR3 regions. We now have used RT-PCR to further characterize the renal expression of T cell receptor (TcR) V beta gene repertoires during the course of this disease. Individual kidneys with focal mononuclear infiltrates characteristic of early alpha TBM disease express up to three different TcR V beta genes; however, the same V beta genes are not found in all kidneys at the same early stage of injury. DNA sequencing of the V beta RT-PCR products reveals a heterogeneous population of VDJ recombinations and deduced CDR3 amino acid sequences. Our studies do not support TcR V beta region gene restriction in histologically-detectable alpha TBM disease, but are more consistent with a dynamic, organ-specific autoimmune disease, directed at multiple autoantigenic epitopes.

Inhibition of leukotriene B4-receptor interaction suppresses eosinophil infiltration and disease pathology in a murine model of experimental allergic encephalomyelitis

Leukotriene B4 (LTB4) is a chemotactic and cell-activating factor present at inflammatory sites in a variety of autoimmune diseases including multiple sclerosis (MS). In this study, we used a murine model of MS, experimental allergic encephalomyelitis (EAE), to assess the potential role of LTB4 on cell infiltration and paralysis. Injection of encephalogenic T cells into naive animals induced paralysis and weight loss that was completely inhibited by treatment with the selective LTB4 receptor antagonist CP-105,696 (ED50= 8.6 mg/kg orally). Although migration of lymphocytes into the central nervous system was unaffected, the efficacious effects of CP-105,696 correlated with up to a 97% decrease in eosinophil infiltration into the lower spinal cord as determined by light and electron microscopy and quantitated by levels of the specific enzyme marker eosinophil peroxidase. These results demonstrate that eosinophil recruitment in EAE is dependent on LTB4 receptor ligation and further reveal a previously unrecognized role for eosinophils in the pathogenesis of this disease.

A myelin oligodendrocyte glycoprotein peptide induces typical chronic experimental autoimmune encephalomyelitis in H-2b mice: fine specificity and T cell receptor V beta expression of encephalitogenic T cells

A predominant response to myelin oligodendrocyte glycoprotein (MOG) was recently observed in patients with multiple sclerosis (MS). To study the possible pathogenic role of T cell response to MOG in MS, we have investigated the encephalitogenic potential of MOG. Synthetic MOG peptides, pMOG 1-21, 35-55, 67-87, 104-117 and 202-218, representing predicted T cell epitopes, were injected into C57BL/6J and C3H.SW (H-2b) mice. The mice developed significant specific T cell responses to pMOG 1-21, pMOG 35-55 and pMOG 104-117. However, pMOG 35-55 was the only MOG peptide which could induce neurological impairment. The highly reproducible disease was chronic, with ascending paralysis and neuropathology comparable with those observed in experimental autoimmune encephalomyelitis (EAE) induced by myelin basic protein or proteolipid protein, except that in H-2b mice the disease was consistently non-remitting. These features differ markedly from those which we recently observed in PL (H-2u) mice with pMOG 35-55-induced disease. In PL mice, pMOG 35-55-induces atypical chronic relapsing EAE, the expression and progression of which are unpredictable. Hence, in different mouse strains, the same MOG peptide can induce typical EAE characterized by ascending paralysis, or atypical EAE with unpredictable clinical signs. pMOG 35-55-specific T cells from H-2b mice recognized an epitope within amino acids 40-55 of the MOG molecule, and pMOG 40-55-reactive T cell lines were encephalitogenic upon transfer into syngeneic recipients. The encephalitogenic pMOG 35-55-reactive C57BL/6J T cell lines expressed V beta 1, V beta 6, V beta 8, V beta 14 and V beta 15 gene segments, and the pMOG 35-55-reactive C3H.SW T cell lines expressed V beta 1, V beta 2, V beta 6, V beta 8, V beta 10, V beta 14, and V beta 15 gene segments. However, in both mouse strains, the utilization of the V beta 8 gene product was predominant (40-43%). The highly reproducible encephalitogenic activity of pMOG 35-55 strongly suggests a pathogenic role for T cell reactivity to MOG in MS and supports the possibility that MOG may also be a primary target antigen in the disease.

Encephalitogenicity of myelin basic protein exon-2 peptide in mice

Immunization with a synthetic peptide with an amino acid sequence corresponding to mouse myelin basic protein exon-2 induced mild experimental allergic encephalitis (EAE) in B10.RIII mice, very mild disease in SJL/J mice and no disease in (SJL x PL)F1 hybrid mice. In contrast, adoptive transfer of an exon-2 peptide-specific T cell line from SJL mice induced severe relapsing EAE in syngeneic recipients. The T cell line was specific for exon-2 peptide and did not cross-react appreciably with an MBP preparation consisting of the 18.5 and 14-kDa isoforms. mRNA for exon-2 containing isoforms could be demonstrated in the spinal cord of SJL/J and B10.RIII mice by amplification using exon-2 and exon-4 oligonucleotide primers. On a relative basis, the level of exon-2 cDNA was lower than that of exon-1 cDNA in the same spinal cord preparations from both strains of mice.

Animal models

Different models of experimental autoimmune encephalomyelitis (EAE) have been successfully applied to investigate and manifold aspects of the autoimmune pathogenesis of multiple sclerosis. Studies using myelin-specific T-cell lines that transfer EAE to naive recipient animals established that only activated lymphocytes are able to cross the endothelial blood-brain barrier and cause autoimmune disease within the local parenchyma. All encephalitogenic T cells are CD4+ Th1-type lymphocytes that recognize autoantigenic peptides in the context of MHC class II molecules. In the case of myelin basic protein (MBP) specific EAE in the Lewis rat, the T-cell response is directed against one strongly dominant peptide epitope. The encephalitogenic T cells preferentially use one particular set of T-cell receptor genes. Although MBP is a strong encephalitogen in many species, a number of other brain protein are now known to induce EAE. These include mainly myelin components (PLP, MAG, and MOG), but also, the astroglial S-100 beta protein. Encephalitogenic T cells produce only inflammatory changes in the central nervous system, without extensive primary demyelination. Destruction of myelin and oligodendrocytes in these models requires additional effector mechanisms such as auto-antibodies binding to myelin surface antigens such as the myelin-oligodendrocyte glycoprotein.

Preferential distribution of V beta 8.2-positive T cells in the central nervous system of rats with myelin basic protein-induced autoimmune encephalomyelitis

To determine the role of encephalitogenic T cells in the formation of lesions in the central nervous system (CNS), experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats by immunization with either myelin basic protein (MBP) or the synthetic peptide which corresponds to the 87-100 sequence of guinea pig MBP, and T cells expressing T cell receptor (TcR) V beta 8.2, V beta 8.5, V beta 10 and V beta 16 in the lymphoid organs and CNS were localized and quantified by flow cytometry (FCM) and immunohistochemistry. In normal rats, the percentage of T cells expressing these V beta phenotypes to the total number of TcR alpha beta+ T cells, as determined by FCM, ranged from 5% to 10% in the lymph node. V beta 16+ T cells were the most predominant population among the four V beta subsets tested. Essentially the same findings were obtained from the analysis of the lymphoid organs of rats with EAE which had been induced by immunization with the same two antigens. In sharp contrast, 15-20% of the T cells isolated from lesions of MBP-induced EAE expressed V beta 8.2. Thus, the percentage of V beta 8.2+ T cells in the EAE lesions was threefold higher than that in the lymph node, while the proportions of V beta 8.5+, V beta 10+ and V beta 16+ T cells were about the same in both organs. The predominance of V beta 8.2+ T cells in EAE lesions was confirmed by counts of immunohistochemically stained T cells in the spinal cord. Moreover, it was revealed that (i) the predominance of V beta 8.2+ T cells was greatest during the development of EAE and became less obvious at the recovery state, and (ii) at the peak stage of EAE, approximately 85% of V beta 8.2+ T cells were distributed in the parenchyma while 15% were in the perivascular space of the CNS vessels. These findings indicate that encephalitogenic T cells which express V beta 8.2 infiltrate the CNS at a very early stage of EAE and become the predominant population in infiltrating T cells, and further suggest that encephalitogenic T cells, not only recruit inflammatory cells in the CNS, but also cause neural tissue damage, such as demyelination.

The T-cell response to myelin basic protein in familial multiple sclerosis: diversity of fine specificity, restricting elements, and T-cell receptor usage

Indirect evidence suggests that an autoimmune response to myelin basic protein (MBP) may be involved in the pathogenesis of multiple sclerosis (MS). In MS, several reports have suggested that restricted T-cell populations respond to MPB, as in inbred rodents with the MS disease model experimental allergic encephalomyelitis. In experimental allergic encephalomyelitis, the T-cell repertoire to MBP varies between strains, and in MS it is likely that the response to MBP is also best defined under conditions where genetic differences between subjects are controlled. In this report, the fine specificity of the T-cell response to MBP was assessed in three families, each with multiple individuals affected with MS. We found that (1) comparable frequencies of MBP-reactive T-cell lines were obtained from peripheral blood of MS patients and their healthy siblings. Human leukocyte antigen (HLA) identical sibling pairs discordant for MS had similar frequencies of MBP-reactive T-cell lines. (2) A broad spectrum of MBP epitopes was recognized by T-cell lines from all individuals studied. Within a family, the fine specificity of MBP recognition showed little or no overlap between individuals, even between HLA identical siblings. (3) Recognition of MBP epitopes occurred in the context of different HLA class II alleles. At least four DR alleles each served as restricting elements for recognition of P82-101 or the carboxy terminal region of MBP, two regions thought to be important in the human T-cell response to the molecule. No relationship between the use of a particular DR allele and a response to a particular region of MBP could be established.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental allergic encephalomyelitis: neutralizing antibody to TGF beta 1 enhances the clinical severity of the disease

Experimental allergic encephalomyelitis (EAE) is a well established model for the human autoimmune disease multiple sclerosis. Recently, we and others have shown that the administration of TGF beta is therapeutically effective in reducing incidence and severity of EAE. Here we show that the addition of anti-TGF beta 1 to myelin basic protein (MBP)-activated lymph node cells enhance the T cell proliferative response by 28% in vitro and in vivo and that injections of anti-TGF beta 1 antibody worsen EAE both in incidence and severity. Further, an inverse relationship was observed in the amount of IL-2 and TGF beta detected in MBP stimulated culture supernatants. We show that IL-2 decreases from 248 U/ml at 48 h to non-detectable at 96 h, while TGF beta increases from 0.5 ng/ml to 1.2 ng/ml, respectively. These observations further indicate a role for endogenous TGF beta 1 in the immunoregulation of EAE.

T cell responses to myelin basic protein in experimental autoimmune encephalomyelitis-resistant BALB/c mice

In strains of mice that are susceptible to experimental autoimmune encephalomyelitis (EAE), cloned CD4+ T cells reactive with autologous myelin basic protein (MBP) have been shown to cause disease when transferred to naive syngeneic recipients. Recent reports indicate that under particular experimental conditions, 'resistant' strains of mice can also develop EAE, although cloned cells have not been isolated and characterized. An analysis of the characteristics of a panel of MBP-specific T cells and the antigen presenting capability of CNS-derived cells obtained from the resistant strain BALB/c is presented here. The data demonstrate that immunization of EAE-resistant BALB/c mice results in the activation of a heterogeneous group of T cells reactive with autologous MBP. Both peripheral antigen presenting cells, as well as microglia isolated from brains of BALB/c mice, are capable of stimulating these cloned MBP-specific T cells to proliferate. When optimally activated in vitro and then injected in vivo into syngeneic BALB/c recipients, three clones studied induced severe cachexia, resulting in loss of up to 35% of body weight before death. Two of the clones also induced clinical and histological EAE, while the third induced only occasional histological evidence of disease. Differences in epitope recognition, T cell receptor usage, cytokine profiles or regulatory mechanisms of self tolerance, may play important roles in preventing potentially destructive autoimmune reactions by these T cells capable of recognizing autologous myelin in the central nervous system.

T cell receptor V beta gene utilization in myelin basic protein specific clones from CXJ1 recombinant inbred mice

CXJ1 mice are a recombinant inbred strain generated from experimental allergic encephalomyelitis (EAE) resistant BALB/c and EAE susceptible SJL/J progenitors. CXJ1 derive their major histocompatibility complex (MHC) class II and TCR genes from the BALB/c progenitor. However, their susceptibility to EAE is similar to SJL/J. Utilizing myelin basic protein (MBP)-specific CD4+ hybridoma clones and a MBP-specific T cell line (TCL) from CXJ1, we found the predominant T cell receptor (TCR) V beta chain expression to be V beta 8 and V beta 13. Our data support the concept of preferential, but not exclusive, TCR V beta usage in the MBP-specific response which is independent of MHC class II haplotype or immunodominant peptide.

Stimulation of T cells by antigenic peptide complexed with isolated chains of major histocompatibility complex class II molecules

Major histocompatibility complex (MHC) class II molecules are heterodimeric glycoproteins with one alpha and one beta polypeptide chain of similar molecular size. In this report, we describe the binding of an acetylated N-terminal peptide of myelin basic protein, [Ala4]MBP-(1-14), to purified individual alpha and beta chains of murine I-Ak molecules. Purified complexes of isolated single chains and antigenic peptide bind to cloned T cells restricted by I-Ak and [Ala4]MBP-(1-14) tetradecapeptide. The binding is blocked by alpha/beta anti-T-cell receptor (TCR) monoclonal antibody. Cell triggering as measured by an increase in extracellular acidification rate is observed when cloned T cells are exposed to purified complexes of isolated chains and antigenic peptide. This increase in the extracellular acidification rate is antigen specific and MHC-restricted, as chains alone or irrelevant chain-peptide complexes do not trigger an increase in the metabolic acidification rate. These results together demonstrate that in vitro cloned T cells are triggered by complexes of specific antigenic peptides and isolated individual chains of their cognate MHC proteins.