Synthesis and cell surface display of class II determinants by long-term propagated rat T line cells

Positional identification of RT1-B (HLA-DQ) as susceptibility locus for autoimmune arthritis

Rheumatoid arthritis (RA) is associated with amino acid variants in multiple MHC molecules. The association to MHC class II (MHC-II) has been studied in several animal models of RA. In most cases these models depend on T cells restricted to a single immunodominant peptide of the immunizing Ag, which does not resemble the autoreactive T cells in RA. An exception is pristane-induced arthritis (PIA) in the rat where polyclonal T cells induce chronic arthritis after being primed against endogenous Ags. In this study, we used a mixed genetic and functional approach to show that RT1-Ba and RT1-Bb (RT1-B locus), the rat orthologs of HLA-DQA and HLA-DQB, determine the onset and severity of PIA. We isolated a 0.2-Mb interval within the MHC-II locus of three MHC-congenic strains, of which two were protected from severe PIA. Comparison of sequence and expression variation, as well as in vivo blocking of RT1-B and RT1-D (HLA-DR), showed that arthritis in these strains is regulated by coding polymorphisms in the RT1-B genes. Motif prediction based on MHC-II eluted peptides and structural homology modeling suggested that variants in the RT1-B P1 pocket, which likely affect the editing capacity by RT1-DM, are important for the development of PIA.

Migratory Activity and Functional Changes of Green Fluorescent Effector Cells before and during Experimental Autoimmune Encephalomyelitis

Homing behavior and function of autoimmune CD4+ T cells in vivo was analyzed before and during EAE, using MBP-specific T cells retrovirally engineered to express the gene of green fluorescent protein. The cells migrate from parathymic lymph nodes to blood and to the spleen. Preceding disease onset, large numbers of effector cells invade the CNS, with only negligible numbers left in the periphery. In early EAE, most (>90%) infiltrating CD4+ cells were effector cells. Migratory effector cells downregulate activation markers (CD25, OX-40) but upregulate several chemokine receptors and adsorb MHC class II on their membranes. Within the CNS, the effector cells are reactivated, with upregulated proinflammatory cytokines and downmodulated T cell receptor-associated structures, presumably reflecting autoantigen recognition in situ.

Class II MHC/Peptide Complexes Are Released from APC and Are Acquired by T Cell Responders During Specific Antigen Recognition

T cell expression of class II MHC/peptide complexes may be important for maintenance of peripheral self-tolerance, but mechanisms underlying the genesis of class II MHC glycoproteins on T cells are not well resolved. T cell APC (T-APC) used herein were transformed IL-2-dependent clones that constitutively synthesized class II MHC glycoproteins. When pulsed with myelin basic protein (MBP) and injected into Lewis rats, these T-APC reduced the severity of experimental autoimmune encephalomyelitis, whereas unpulsed T-APC were without activity. Normal MBP-reactive clones cultured without APC did not express class II MHC even when activated with mitogens and exposed to IFN-γ. However, during a 4-h culture with T-APC or macrophage APC, recognition of MBP or mitogenic activation of responder T cells elicited high levels of I-A and I-E expression on responders. Acquisition of class II MHC glycoproteins by responders was resistant to the protein synthesis inhibitor cycloheximide, coincided with transfer of a PKH26 lipophilic dye from APC to responders, and resulted in the expression of syngeneic and allogeneic MHC glycoproteins on responders. Unlike rested I-A− T cell clones, rat thymic and splenic T cells expressed readily detectable levels of class II MHC glycoproteins. When preactivated with mitogens, naive T cells acquired APC-derived MHC class II molecules and other membrane-associated proteins when cultured with xenogeneic APC in the absence of Ag. In conclusion, this study provides evidence that APC donate membrane-bound peptide/MHC complexes to Ag-specific T cell responders by a mechanism associated with the induction of tolerance.

Immunological self/nonself discrimination: integration of self vs nonself during cognate T cell interactions with antigen-presenting cells

The hypothesis is presented that immunological integration of nonefficacious vs efficacious T cell antigen receptor (TCR) signals are foundational for self/nonself discrimination and that multiple integrative mechanisms are intrinsic to the molecular to molar organization of an adaptive immune response. These integrative mechanisms are proposed to adaptively regulate expression of costimulatory signals, such that foreign proteins are associated with the expression of costimulatory signals, whereas self-proteins are associated with the lack of costimulatory signaling. Overall, this model offers several unique contributions to the study of immunology. First, this model postulates that cognate TCR/major histocompatibility complex (MHC) interactions are sufficient to adaptively mediate immunological self/nonself discrimination. This model thereby offers a unique alternative to models that largely rely on innate immunity to prime immune discrimination. Second, the integrative model argues that the immune system can simultaneously reinforce self-tolerance and promote immunity to foreign organisms at the same time and in the same location. Many alternative models presume that pathogenic self-reactive T cells do not exist at the outset of an immune response against foreign agents. Third, the integrative model uniquely predicts relationships between immunodeficiency and autoimmune pathogenesis. Fourth, this model illustrates the regulatory advantages of cognate antigen presenting cell (APC) systems (i.e., T cell or B cell APC) compared to nonspecific APC. Cognate APC systems together with the respective clonotypic responders may comprise a fundamental "network" of lymphoid cells. Such networks would have clone-specific regulatory capabilities and may be central for immunological self/nonself discrimination. Fifth, this model provides an explanation for "infectious" tolerance without creating specialized subsets of "suppressor" or "regulatory" T cells. Each mature T cell retains the potential to reinforce tolerance or mediate immunity, depending on the specific antigenic cues present in the immediate environment.

Vesicles bearing MHC class II molecules mediate transfer of antigen from antigen-presenting cells to CD4+ T cells

Previous studies have provided evidence that myelin basic protein (MBP)-specific rat T cells acquire antigen via transfer of preformed peptide/MHC class II complexes from splenic antigen-presenting cells (APC). The purpose of the present study was to determine how T cells acquire peptide/MHC class II complexes from APC in vitro. Our results show that a MHC class II+ T cell line, R1-trans, released MHC class II-bearing vesicles that directly stimulated MBP-specific CD4+ T cells. Vesicles expressing complexes of MHC class II and MBP were also specifically cytotoxic to MBP-specific T cells. Surviving T cells acquired MHC class II/antigen complexes from these vesicles by a mechanism that did not require protein synthesis but depended on specific TCR interactions with peptide/self MHC complexes. Furthermore, MBP/MHC class II-bearing vesicles enabled T cells to present MBP to other T cell responders. These studies provide evidence that APC release vesicles expressing preformed peptide/MHC class II complexes that interact with clonotypic TCR, allowing MHC class II acquisition by T cells. Vesicular transport of antigen/MHC class II complexes from professional APC to T cells may represent an important mechanism of communication among cells of the immune system.

Antigen presentation by T cells: T cell receptor ligation promotes antigen acquisition from professional antigen-presenting cells

The purpose of this study was to determine whether the clonotypic specificity of the T cell receptor influences the specificity of T cell-mediated antigen presentation. We have previously shown that myelin basic protein (MBP)-specific Lewis rat GP2.E5/R1 (R1) T cells cultured with antigen, irradiated syngeneic splenocytes (IrrSPL) and tolerogenic monoclonal antibody become highly effective antigen-presenting cells (APC). In the current studies, we investigated the transfer of specific (MBP) and unrelated (conalbumin) antigens from antigen-pulsed SPL to R1 T cells. R1 T cells cultured with IrrSPL that were pulsed simultaneously with both MBP and conalbumin acquired and presented both antigens to the appropriate T cell responders in a secondary assay. These results suggested a physical transfer of major histocompatibility complex (MHC)/peptide complexes from professional APC to R1 T cells. Transfer of conalbumin from professional APC to R1 T cells required specific recognition of MBP and was optimal when both conalbumin and MBP were presented on the same group of professional APC. Antigens transfer did not occur when allogeneic SPL were used as APC. The anti-I-A mAb OX6 inhibited antigen transfer but only when added during the initiation of culture. OX6 also inhibited antigen acquisition by R1-trans, a variant of the R1 T cell line which constitutively synthesizes high levels of I-A, from MBP-pulsed IrrSPL but blockade of I-A did not inhibit antigen acquisition when soluble MBP was added directly to the culture. Despite constitutive synthesis of I-A, R1-trans T cells did not acquire guinea pig MBP from pulsed allogeneic APC. These studies demonstrate that although T cells of a particular specificity can present unrelated antigens, the cognate interaction of the T cell antigen receptor with the appropriate antigen/self-MHC complex strongly promotes acquisition of these complexes from professional APC.

Tumor necrosis factor blockade in actively induced experimental autoimmune encephalomyelitis prevents clinical disease despite activated T cell infiltration to the central nervous system

Recently, we demonstrated that experimental autoimmune encephalomyelitis (EAE) in the rat, passively transferred using myelin basic protein (MBP)-reactive encephalitogenic CD4+ T cells, was preventable by administration of a p55-tumor necrosis factor-IgG fusion protein (TNFR-IgG). This was despite quantitatively and qualitatively normal movement of these MBP-specific T cells to the central nervous system (CNS). To extend these findings, the effect of TNFR-IgG on EAE actively induced by injection of MBP in complete Freund's adjuvant was examined. This form of EAE in the rat typically involves an acute, self-limiting neurological deficit, substantial CNS inflammation, but minimal demyelination. Here we show that administration of TNFR-IgG prior to onset of disease signs completely prevented the neurological deficit or markedly reduced its severity. This blockade of clinical disease was dissociated from weight loss which occurred at the same tempo and magnitude as in control rats exhibiting neurological signs of disease such as paralysis. The timing of TNF blockade was critical as established clinical disease was relatively refractory to TNFR-IgG treatment. Activated CD4+ T cells expressing normal or elevated levels of VLA4, major histocompatibility complex class II, MRC OX40 and CD25 were isolated from or immunohistochemically localized in the CNS of clinically healthy rats treated before disease onset. There was a reduction of the amount of other inflammatory leukocytes in the CNS of these treated animals but, more importantly, the activation state of inflammatory leukocytes, as well as that of microglia isolated from treated animals, was reduced. Thus, TNFR-IgG, when administered before disease onset, appears to act by inhibiting an effector function of activated T cells and possibly other inflammatory leukocytes necessary to bring about the neurological deficit. However, while TNF is a critically important cytokine for the early events leading to initiation of EAE, it is not a necessary factor in the acute neurological deficit characteristic of this form of EAE, once disease onset has occurred.

Costimulatory signalling potential of murine MHC class II-positive T-clone cells

Activated human and rat T cells as well as mouse T-cell clones have been reported to synthesize and express major histocompatibility complex (MHC) class II molecules. However, the capacity of class II+ antigen (Ag) presenting T cells to induce proliferation of Ag-specific cloned T cells has been controversial. We analysed whether the failure of some T-cell clones to proliferate in response to Ag presented by class II+ T cells is because of a lack of costimulatory cytokine production by the antigen-presenting cells (APC). As a model system the mouse class II+ cloned BI/O4.1 T cells were used as APC in order to activate the T cell clone KIII5. This T-helper 1 (Th1) type, GAT (synthetic copolymer of L-glutamic acid, L-alanine and L-tyrosine)-specific clone is characterized by an efficient downregulation of interleukin-2 receptor (IL-2R) with time following antigenic stimulation. KIII5 cells respond to GAT-presenting splenic antigen-presenting cells (APC) by IL-2 production, IL-2R upregulation and proliferation. When BI/O4.1 T cells were used as APC, KIII5 cells produced IL-2, but did not proliferate. Reverse transcriptase-polymerase chain reaction (RT-PCR) revealed a lack of IL-12 production by BI/O4.1 cells. Addition of IL-12 to a coculture of Ag-presenting BI/O4.1 cells and KIII5 cells fully reconstituted a proliferative response. IL-12 in synergy with IL-2 upregulated IL-2R alpha chain expression and enhanced proliferation of KIII5 cells. Our data suggest, that class II+ T cells are not functional in inducing Ag-mediated expansion of resting Th1 cells owing to their failure to produce IL-12, but rather that they play a role in amplification loops during an ongoing immune response.

Expression of major histocompatibility complex class II molecules in rat T cells

The expression of major histocompatibility complex (MHC) class II molecules in murine T cells has been controversial. We therefore reexamined the transcription, synthesis and surface expression of MHC class II determinants in rat T cells both in vivo and in vitro. In naive rats, a large proportion of small CD4+8+ and mature CD4+8-/CD4-8+ thymocytes was found to be MHC class II positive. At least some of the MHC class II molecules found on thymocytes were actively synthesized. The synthesis of MHC class II proteins was detected in peripheral T cells activated in vivo during induction of experimental allergic encephalomyelitis (EAE). A proportion of T cells from the inflammatory lesion of EAE exhibited MHC class II on the surface. A panel of helper T cell lines and clones was shown to synthesize MHC class II proteins. In a prototypic clone, a weak constitutive expression of MHC class II was observed. During activation, the rate of endogenous MHC class II synthesis increased and passive absorption of surface MHC class II from other cells occurred. Our data demonstrate the expression of MHC class II molecules in rat T cells in both the thymus and periphery. Since the primary function of MHC class II molecules is the presentation of peptide epitopes to T cells, these results call attention to the possible role of MHC class II molecules in T-T interactions during T cell maturation and activation.

An LI and ML motif in the cytoplasmic tail of the MHC-associated invariant chain mediate rapid internalization

Invariant chain (Ii) is a transmembrane protein that associates with the MHC class II molecules in the endoplasmic reticulum. Two regions of the 30 residue cytoplasmic tail of Ii contain sorting information able to direct Ii to the endocytic pathway. The full-length cytoplasmic tail of Ii and the two tail regions were fused to neuraminidase (NA) forming chimeric proteins (INA). Ii is known to form trimers and when INA was transfected into COS cells it assembled as a tetramer like NA. The INA molecules were targeted to the endosomal pathway and cotransfection with Ii showed that both molecules appeared in the same vesicles. By labelling the INA fusion proteins with iodinated antibody it was found that molecules with either endocytosis signal were expressed at the plasma membrane and internalized rapidly. Point mutations revealed that an LI motif within the first region of the cytoplasmic tail and an ML motif in the second region were essential for efficient internalization. The region containing the LI motif is required for Ii to induce large endosomes but a functional LI internalization motif was not fundamental for this property. The cytoplasmic tail of Ii is essential for efficient targeting of the class II molecules to endosomes and the dual LI and ML motif may thus be responsible for directing these molecules to the endosomal pathway, possibly via the plasma membrane.

Common peptide epitope in mumps virus nucleocapsid protein and MHC class II-associated invariant chain

The present study describes a 7 amino acid-long sequence (YQQQGRL) which is identical in HLA-associated invariant chain and mumps virus nucleocapsid protein and is additionally followed by one conservative amino acid pair. As such a long amino acid homology is extremely rare in two evolutionarily unrelated proteins the possibility that it could induce immunological cross-reactivity was evaluated. Several antigenicity indices suggested high antigen potential within this region. Synthetic peptides containing this sequence were reactive with 31% of monoclonal antibodies specific for mumps virus nucleocapsid protein in ELISA. High antibody levels against this epitope were found in 7% of mumps-seropositive human sera and antibody levels clearly increased after natural mumps infections and mumps vaccinations. Rabbit antibodies raised against a synthetic invariant chain peptide AYF-LYQQQGRLDKL-C reacted with corresponding nucleocapsid peptide RFAKYQQQGRLEAR-C and antibodies against the nucleocapsid peptide reacted with the invariant chain peptide. Rabbit antibodies against the invariant chain peptide also reacted with nucleocapsid molecules in formaldehyde-fixed mumps virus-infected cells, and antibodies against the nucleocapsid peptide reacted with invariant chains expressed in methanol-fixed cells. One monoclonal antibody specific for the nucleocapsid molecule also reacted with cells expressing invariant chains. In immunoprecipitation rabbit antibodies against the invariant chain peptide bound to invariant chains while antibodies against the nucleocapsid peptide did not. The results suggest that there is antigenic similarity in mumps virus nucleocapsid molecule and HLA-associated invariant chain which may cause immunological cross-reactivity between these molecules.

Diverse T cell receptor beta chain usage by rat encephalitogenic T cells reactive to residues 68-88 of myelin basic protein

Encephalitogenic T cells not only cause experimental autoimmune encephalomyelitis (EAE), but they induce resistance against subsequent induction of the disease as well. The T cell receptor (TcR) of encephalitogenic T cells is believed to contribute to their vaccinating activity. Findings in support of this assumption include the apparent restricted use of particular TcR elements, such as V beta 8.2. However, results from other laboratories including ours do not support this idea. We previously showed that rat T cells reactive against the conserved encephalitogenic epitope of myelin basic protein [MBP (87-99)] use the TcR in a heterogeneous fashion (Sun, D. et al., Eur. J. Immunol. 1992. 22: 591). Here we show, in Lewis rats, that the TcR beta chain usage of T cells specific for the dominant MBP (68-88) epitope is not restricted to V beta 8.2. Not only did such cells rely on diverse V beta chains, but some non-V beta 8-bearing cells were highly encephalitogenic. We also show that antigen-presenting cells (APC) play an important role in determining the TcR usage of MBP-specific T cells. Stimulation of MBP (68-88)-specific T cell lines by cloned APC derived from different sources resulted in selection of encephalitogenic T cells bearing different TcR beta chains.

Cell surface display of rat invariant gamma chain: detection by monoclonal antibodies directed against a C-terminal gamma chain segment

A series of 14 monoclonal antibodies (mAb) directed against the C-terminal part of the rat invariant gamma chain (amino acid 142-216) was generated using distinct fusion proteins that contain this gamma segment for immunization and hybridoma screening. Additional fusion protein were prepared carrying discrete regions of the gamma chain. Employing these reagents confirmed that the obtained mAb do indeed recognize the C-terminal portion of the invariant chain, as demonstrated by Western blot analysis. All mAb established recognize epitopes present on the native gamma chain, as revealed by immunoprecipitation analysis using nonionic detergent extracts of metabolically labeled Lewis rat splenocytes combined with two-dimensional gel electrophoresis. However, while the majority of the gamma chain-specific mAb precipitated gamma chain-containing polypeptide chain complexes in which immature, sialic acid-deficient and mature, terminally sialylated forms of the gamma chain were predominantly represented, a fraction of the antibodies preferentially precipitated the immature gamma forms. Cell surface binding of these two groups of mAb correlated with the immunoprecipitation data in that the former group of antibodies did bind to intact Lewis rat spleen cells, while essentially no binding was observed with the antibodies of the latter group. Double-fluorescence staining with the class II-specific fluorescein isothiocyanate-conjugated mAb OX3 and OX6, respectively, as well as a representative gamma chain-specific mAb visualized with phycoerythrin-coupled secondary antibody shows coexpression of class II determinants and the invariant chain at the cell surface.

Immune regulation in self tolerance: functional elimination of a self-reactive, counterregulatory CD8+ T lymphocyte circuit by neonatal transfer of encephalitogenic CD4+ T cells lines

Transfer of encephalitogenic, CD4+ T lymphocyte lines into syngeneic adult Lewis rats not only leads to the development of experimental autoimmune encephalomyelitis (EAE), but, in addition, to the expansion of counterregulatory, CD8+ T lymphocyte clones which are able to lyse specifically the encephalitogenic T cells in vitro and to neutralize their encephalitogenic capacity in vivo. In striking contrast, in neonatal rats, which still lack myelin (autoantigens), injection of the same encephalitogenic lines neither mediates EAE, nor confers protection in later life against the myelin-specific T cells. In fact, this treatment results in the life-long functional elimination of counterregulatory, clonotypic CD8+ T lymphocytes, which cannot even be reinduced by repeated injections of the relevant CD4+ T line. These data seem to point to a self-protective T cell control mechanism which is developed within the immune system prior to, and thus independent of the appearance of the appropriate self antigen.

Biochemical properties of MHC class II molecules endogenously synthesized and expressed by mouse Langerhans cells

The cell surface expression and biosynthesis of Langerhans cells (LC)-derived major histocompatibility complex (MHC) class II molecules from epidermal cells (EC) prepared freshly and cultured for up to 3 days was investigated. Based on the constitutive expression of MHC class II determinants by LC, a panning and magnetic bead selection procedure was employed, yielding 65% and 86% of I-A+ cells, respectively. Phenotypical and cytochemical examinations revealed that the two LC preparations were free of contaminating macrophages as well as B and T cells. Freshly prepared enriched LC were highly efficient in the stimulation of protein antigen-specific T cell clones, while LC purified from short-term cultured EC suspensions proved to be more efficient allogeneic stimulator cells than fresh LC. Comparative analysis of LC obtained from freshly prepared and from short-term-cultured EC preparations indicated an up-regulation of MHC class II determinants during short-term culture. Radioiodination analysis of LC selected by magnetic beads demonstrated prominent class II alpha and beta chain signals with only a minute fraction of invariant chains p35 and p45 being expressed at the cell surface. Unlike class II complexes derived from B cells, those from LC contained invariant chain fragment p20 in association with alpha/beta heterodimers at the plasma membrane. No qualitative differences between freshly isolated and 3-day cultured LC in cell surface expressed MHC class II components were detectable. Metabolic labeling with subsequent two-dimensional electrophoresis revealed distinct features of LC-derived MHC class II molecules with a high proportion of invariant chains in particular gamma and p40 and their extensive sialylation. While fresh and 1-day cultured LC exhibited appreciable levels of newly synthesized class II molecules, a dramatic down-regulation in class II and invariant chain synthesis was measured after 3 days of continuous in vitro culture.

CD4 rat x rat and mouse x rat T cell hybridomas produced by fusion of established T cell lines and clones to W/Fu (C58NT)D

Previously, fusion of established T cell lines or clones has been claimed to be difficult. We now report our experiences in the fusion of both long term cultures of rat T cell clones and mouse T cell lines to rat W/Fu (C58NT)D. Upon fusion of rat T cell clones the hybrids obtained expressed antigen specificities identical to those of the parent clones. In addition, C58 was used for interspecies hybridisation of murine T cell lines. The specificity of intra- and inter-species hybrids was maintained by subcloning. We conclude that the C58 cell line can be used to generate continuously growing monoclonal T-cell reagents of sufficient stability using both intra- and inter-species hybridisation.

Clonotypic chromosomal aberrations in long-term lines of myelin-specific rat T lymphocytes

A panel of 16 long-term rat T lymphocyte lines and clones were screened for cytogenetical abnormalities using chromosomal banding techniques. All T lines were CD4+, recognizing the relevant antigen in the molecular context of major histocompatibility complex (MHC) class II determinants. With one exception (an ovalbumin-specific line), all lines were specific for myelin proteins, and apart of one BS rat-derived T line and its clones, all lines were selected from the Lewis strain of rat. After in vitro culture of more than 1 year, all lines and clones exhibited subtle but definite chromosomal aberrations, which included deletions, enlargement, translocations and formation of isochromosomes. All lines were near diploid, structural chromosomal changes being more frequent than numerical abnormalities. Each T line investigated had an individual pattern of chromosomal changes. In our analysis, 16 of the 22 different chromosomes had changes in at least one line. Chromosome 9 and the X chromosome appeared to have an enhanced susceptibility of alterations. In two cases, chromosomal markers could be traced through different stages of in vitro culture of the T lines.

Translation in Xenopus laevis oocytes of hybrid selected LEW rat RT1.B alpha- and beta-chain transcripts results in serologically discrete class II polypeptide chain complexes

Using the non-crossreactive mAb MRC-OX3 and MRC-OX6, two serologically distinct RT1.B-specific (I-A equivalent) alpha, beta heterodimers have previously been described by us as residing at the cell surface of LEW rat spleen cells. The two-chain elements were suggested to represent stable conformation isomers, diverged by dissociation of the mature gamma-chain from a mAb MRC-OX6 reactive biosynthetic intermediate, composed of terminally glycosylated alpha-, beta- and gamma-chains. In this study we addressed the question of whether or not the presence of terminally glycosylated invariant gamma-chain was obligatory for the formation of the two MRC-OX3 and MRC-OX6 reactive two-chain complexes. The synthesis of RT1.B-specific alpha, beta heterodimers was therefore initiated, in the absence of accompanying invariant gamma-chains, by microinjecting hybrid-selected RT1.B alpha- and beta-specific mRNA into oocytes of Xenopus laevis for translation. Class II molecules produced were analyzed by affinity chromatography of radioactive-labeled oocyte detergent lysates using the appropriate monoclonal immunoadsorbents for identification. Although rat gamma-chain mRNA was excluded in this assay system, distinct MRC-OX3 and MRC-OX6 reactive two-chain complexes were detected by two-dimensional gel electrophoresis. These findings clearly indicate that the formation of the two RT1.B-specific alpha, beta heterodimers is independent of the presence of the rat invariant gamma-chain.

T cell receptor beta chain usage in myelin basic protein-specific rat T lymphocytes

Myelin basic protein (MBP)-specific T cell lines and clones have been established from rats of the major histocompatibility complex (MHC)-compatible Lewis and BS strains. All lines and clones are MHC class II restricted and share the CD4+ phenotype. The cells proliferate specifically in response to either a peptide representing amino acids #68-88 of guinea pig MBP, to residues #47-67 or to an unidentified myelin antigen which is distinct from MBP. All lines and clones specific for MBP express the same T cell receptor (TcR) variable (V) beta chain element, which is homologous to the mouse V beta 8.2 gene segment. Three lines/clones with the same antigen fine specificity have identical V beta D beta J beta junctions on the protein level, a region which represents part of the potential antigen-binding portion of the TcR; two of the lines express members of the V alpha 2 family. These results suggest biased usage of TcR V beta elements in rat T cells specific for MBP. Our findings broaden the basis for a rational therapeutic strategy to specifically intervene in the rodent model system of experimental allergic encephalomyelitis.