The antigen-specific, major histocompatibility complex-restricted receptor on T cells. VI. An antibody to a receptor allotype

Extrathymic tolerance of mature T cells: clonal elimination as a consequence of immunity

The mechanism by which T lymphocytes are tolerized to self or foreign antigens is still controversial. Clonal deletion is the major mechanism of tolerance for immature thymocytes; for mature T cells, tolerance is considered to reflect anergy rather than deletion, and to be a consequence of defective presentation of antigen. This paper documents a novel form of tolerance resulting when mature T cells encounter antigen in immunogenic form. Evidence is presented that exposure of mature T cells to Mlsa antigens in vivo leads to specific tolerance and disappearance of Mlsa-reactive V beta 6+ T cells. Surprisingly, the clonal elimination of V beta 6+ cells is preceded by marked expansion of these cells. Thus, tolerance induction can be the end result of a powerful immune response. These data raise important questions concerning the relationship of tolerance and memory.

Mechanisms of autoimmunity in the context of T-cell tolerance: insights from natural and transgenic animal model systems

There are a number of mechanisms which cooperate to produce and maintain T-cell tolerance. First, and perhaps most important, is the clonal deletion in the thymus of T cells with high affinity for self antigens. However, to ensure that a wide repertoire of T cells is available in the periphery to combat foreign antigens, the threshold of clonal deletion may be set low enough so that T cells whose TCR's have sub-threshold affinity for self antigens mature and migrate to the periphery. T cells which recognize self antigen-derived peptides not expressed or presented in the thymus will also fail to be deleted. For those self-reactive T cells which are not deleted in the thymus, other mechanisms may produce tolerance, including an undefined alteration of signalling pathways which produces clonal anergy, and lowering the avidity of the TCR for its ligand by downregulating coreceptor and accessory molecules. Active suppression of T-cell responses in another well-described phenomenon whose mechanism is undefined. From our observations with the model systems discussed here, we have observed three distinct mechanisms by which T-cell tolerance can be circumvented, allowing autoimmune phenomena to occur. These mechanisms may have relevance for different types of autoimmune diseases seen in humans. In gld mice, the autoimmune disease seems to be related to a global defect in T-cell differentiation and function, which allows for the expansion of autoimmune B cells. While we showed that clonal deletion of V beta-bearing T cells is appropriate in certain cases, aberrant lymphokine secretion by the abnormal T cells or disruption of immune system regulation are most probably responsible for allowing autoantibody production. While human lupus erythematosis shares much of the pathology of lpr and gld mice, there is no expansion of T cells with a similar phenotype in human lupus. There are environmental factors which must play a role in the development of human lupus, since the incidence of the disease does not follow an absolute genetic pattern. The escape from clonal deletion and subsequent reactivation of autoimmune T cells which we observed in V beta 8.1 TCR-transgenic mice can be a model for human autoimmune diseases such as multiple sclerosis and type I diabetes, in which T cells are directed against a specific autoantigen. According to this model, susceptibility loci for autoimmune disease such as the MHC would function by producing different repertoires of T cells which in some cases could gain autoreactivity following activation.(ABSTRACT TRUNCATED AT 400 WORDS)

T-cell receptor and autoimmune disease

Since the genes encoding the TCR have been cloned, their structure, organization, pattern of rearrangement, diversification and expression in ontogeny have been classified. However, there are still many important questions to be addressed, such as the nature of thymic education, tolerance, the mechanism of MHC-restricted antigen recognition and the relation between TCR repertoire and autoimmunity. In the future, new approaches to study these issues, such as transgenic mice, X-ray crystallography, and severe combined immune deficiency mice reconstituted with human hematopoietic cells will lead to a more profound understanding of these questions. This will hopefully allow us to manipulate the immune response in different and more effective ways than are currently available.

Failure of clonal deletion in neonatally thymectomized mice: tolerance is preserved through clonal anergy

Self-tolerance is achieved in part through intrathymic deletion of self-reactive T cells. The necessity of the thymus for this process is suggested by the development of autoimmune diseases in neonatally thymectomized (neoTx) mice and by the failure of clonal deletion in nude mice. Indeed, the present study demonstrates that neonatal thymectomy on day 3 after birth results in the failure of clonal deletion of V beta 11+ T cells in BALB/c mice and V beta 5+ and V beta 6+ T cells in DBA/2 mice. However, these potentially autoreactive cells are nonfunctional as measured by proliferation and lymphokine production after stimulation with appropriate anti-V beta mAbs or stimulator cells. It appears that this induction of nonresponsiveness may have occurred extrathymically: the early neonatal thymus (presumably the source of the peripheral T cells observed in neoTx mice) also contains T cells with self-reactive receptors, but these cells are fully functional. Therefore, neonatal thymectomy aborts deletion of self-reactive T cells, but self-tolerance is maintained through functional inactivation of potentially self-reactive clones.

A human TCR-Ig chimeric protein used to generate a TCR alpha chain variable region-specific mAb

In a recent report, a construction containing the alpha chain-variable region (V alpha) coding sequence of a cDNA clone derived from a diphtheria toxoid-specific human T cell (P28), fused to a human immunoglobulin kappa light chain constant region (Ck), was used stably to transfect a murine myeloma cell. In the present study, these transfected cells were employed as an immunogen to raise a mAb, termed 1C5V alpha, specific both for the V alpha Ck chimeric protein secreted by the transfectant and the P28 T cell antigen receptor-V alpha region. mAb 1C5V alpha specifically immunoprecipitates the V alpha Ck protein as a family of 32-35 kDa bands present in the 35S-methionine-labeled culture supernatant from the transfected cells. It specifically binds clone P28. Surface molecules recognized by mAb 1C5V alpha are physically linked to the CD3 molecules since cell treatment with either 1C5V alpha or anti-CD3 mAbs caused the simultaneous down-regulation of the CD3/TCR molecular complex. This link is further supported by immunoprecipitation experiments. Thus, both the 1C5V alpha and the anti-CD3 mAbs precipitate the 16-28 kDa CD3 molecules and the disulfide-linked form of P28 TCR from 125I-labeled P28 T cells. Studies performed in order to define whether a stimulus directly acting on the TCR-V alpha region may trigger the intracellular events observed during human T cell activation showed that (a) mAb 1C5V alpha efficiently triggers the phospholipase C transduction pathway revealed by an accelerated phosphoinositides turn-over and an increased production of phosphorylated derivatives of inositol phosphates; (b) mAb 1C5V alpha induces an up-regulation of IL2R mRNA, accompanied by a slight increase of IL2 and IFN alpha mRNA transcripts evidently amplified in the presence of PMA; (c) soluble mAb 1C5V alpha is strongly mitogenic together with PMA. These results provide the first evidence for the structural authenticity of a secreted water-soluble chimeric form of the variable region of a human TCR alpha chain. They further demonstrate that such chimeric proteins may be valuable tool to further dissect the various functional structure of the human TCR.

Inside the thymus, Mls antigen is exclusively presented by B lymphocytes

The ability to stimulate an Mls-1 mixed lymphocyte reaction (MLR) is predominantly expressed by low density B lymphocytes in the spleen and peritoneal cavity of normal adult mice, and is absent in splenic B cells 1 month after lethal irradiation and reconstitution from autologous bone marrow. Coreconstitution of these mice with normal syngeneic peritoneal cells restores the stimulatory potential of splenic B cells, but sorted CD5+ or CD5- IgM+ lymphocytes from peritoneum are equally good stimulators, suggesting that functional Mls-1 expression may require long life spans and selection. Bone-marrow-reconstituted DBA/2 mice that fail to express Mls-1 antigens in the periphery nevertheless maintain T-cell receptor V beta 6 and 8.1 deletions among the newly formed T cells. These findings led us to directly investigate the Mls stimulatory ability of purified antigen-presenting cell populations inside the thymus. We report here that thymic B lymphocytes seem to represent the only intrathymic cell population able to stimulate Mls-1 MLR.

Selective anergy of V beta 8+,CD4+ T cells in Staphylococcus enterotoxin B-primed mice

The cellular basis of the in vitro and in vivo T cell responses to Staphylococcus enterotoxin B (SEB) has been investigated. The proliferation and cytotoxicity of V beta 8.1,2+,CD4+ and CD8+ T cells were observed in in vitro response to SEB. In primary cytotoxicity assays, CD4+ T cells from control spleens were more active than their CD8+ counterparts, however, in cells derived from SEB-primed mice, CD8+ T cells were dominant in SEB-specific cytotoxicity. In vivo priming with SEB abrogated the response of V beta 8.1,2+,CD4+ T cells despite the fact that these cells exist in significant number. This SEB-specific anergy occurred only in V beta 8.1,2+,CD4+ T cells but not in CD8+ T cells. These findings indicate that the requirement for the induction of antigen-specific anergy is different between CD4+ and CD8+ T cells in post-thymic tolerance, and the existence of coanergic signals for the induction of T cell anergy is suggested.

Sequence and diversity of bovine T-cell receptor beta-chain genes

The nucleotide sequences of 38 T-cell receptor (Tcr) beta-chain cDNA clones which were isolated from a cDNA library (2 x 10(6) plaques) constructed from bovine peripheral blood lymphocytes were determined. Of 38 cDNA clones, 22 were rearranged and contained the functional variable (V) gene segments. These clones were tentatively divided into nine Tcrb-V gene families which correspond to the human Tcrb-V family. Among them, a Tcrb-V12 gene segment was isolated from 9 out of 22 clones, suggesting that this Tcrb-V family was expressed in the bovine peripheral blood lymphocytes. Two different constant (C) gene segments were found, and both C regions were composed of 178 amino residues. The amino acid sequences of bovine Tcrb-C regions are approximately 80%-82%, 78%, and 78% similar to those from human, mouse, and rabbit, respectively. To estimate Tcrb-V-associated restriction fragment length polymorphisms (RFLPs), Southern blot analysis was performed using liver DNAs from four bovine breeds, Holstein, Angus, Hereford, and Japanese Black. However, no significant difference was observed among genomic DNAs of Tcrb-V loci from these four breeds.

Mutations in the major histocompatibility complex class I antigen-presenting groove affect both negative and positive selection of T cells

In several transgenic mouse models T cell development was shown to be controlled by the binding of the alpha/beta T cell receptor (TcR) to ligands in the thymus. In transgenic mice expressing a male-specific TcR alpha/beta, the presence of the restricting D major histocompatibility complex (MHC) molecule plus the male specific peptide deleted thymocytes at an early stage of development. On the other hand, maturation of T cells required an interaction of the TcR with the thymic D MHC molecules in the absence of specific peptides. This could imply that negative and positive selection of this receptor are affected differently by mutations in the HY peptide-binding groove of the D MHC molecule. Such mutants have been isolated and were shown to affect the response to HY antigen in that both the bm14 (residue Glu70----Asp) and the bm13 (residue Leu114----Glu, Phe116----Tyr and Glu119----Asp) strains do not normally mount cytotoxic responses to male cells. Here we show that these mutations affect antigenicity of male cells, as well as negative and positive selection of T cells in TcR alpha/beta transgenic mice.

Self-reactive T cells can escape clonal deletion in T-cell receptor V beta 8.1 transgenic mice

To study the mechanisms of tolerance in detail, we have constructed transgenic mice expressing a V beta 8.1-D beta 2-J beta 2.3-C beta 2 T-cell receptor (TCR) gene. Since expression of V beta 8.1 is known to correlate with reactivity of CD4+CD8- T cells to minor lymphocyte-stimulating locus 1a (Mls-1a), we expected to induce tolerance in most CD4+CD8- T cells in V beta 8.1 transgenic mice of the Mls-1a allele. In one line of Mls-1b V beta 8.1 transgenic mice, the V beta 8.1 TCR was expressed on greater than 98% of mature T cells and their response to Mls-1a was highly enriched. In Mls-1a V beta 8.1 transgenic mice, CD4+CD8- T cells in these mice were severely reduced among both peripheral T cells and thymocytes. However, the deletion of these cells was not complete, and most of the residual CD4+CD8- mature T cells still expressed normal densities of V beta 8.1 TCR. The residual CD4+CD8- T cells did not respond to Mls-1a but were still able to proliferate in response to other stimuli via the TCR. Interestingly, CD4+CD8- V beta 8.1+ T-cell clones isolated from Mls-1a V beta 8.1 transgenic mice could respond to Mls-1a. We suggest that these types of T cells escape clonal deletion in the thymus.

Participation of a dominant cytotoxic T cell population defined by a monoclonal antibody in syngeneic anti-tumor responses

Cytotoxic T lymphocyte (CTL) clones against a syngeneic Friend virus-induced erythroleukemia (FBL-3) were generated in C57BL/6 (B6) mice. A monoclonal antibody (mAb, N9-127) was then raised from spleen cells of a B6 mouse immunized syngenically against one of these CTL clones. This mAb detected the epitope (127Ep) of the T cell antigen receptor (TcR) on the immunizing CTL clone in tests of immunoprecipitation, specific blocking and proliferation, and induction of TcR-mediated nonspecific lysis of the clone. In addition, more than 10% of the FBL-3-specific CTL clones isolated independently from B6 mice were 127Ep+. Further investigations revealed that up to 30% of B6 anti-FBL-3 T cell blasts from mixed lymphocyte tumor cell cultures were positive for this epitope, and that its expression was confined to CD8+ T cells. This epitope was not detected in naive lymphoid cells from the spleen, lymph nodes or thymus or in T cell clones specific for tumors other than FBL-3. The FBL-3-specific CTL clones were next grouped into 127Ep+ and 127Ep- clones. Sequence analyses of the CTL clone used for immunization showed the rearrangements of V alpha 1J alpha 112-2 and V beta 10D beta 2.1J beta 2.7. Southern blot analysis of all the 127Ep+ CTL clones examined showed the same DNA rearrangement bands of both the TcR alpha and beta genes. These findings suggested that mAb N9-127 recognized the shared determinant of the TcR molecule which was expressed by the dominant CTL population in the response to FBL-3.

The requirement of intrathymic mixed chimerism and clonal deletion for a long-lasting skin allograft tolerance in cyclophosphamide-induced tolerance

Mechanisms of cyclophosphamide (CY)-induced tolerance were studied. When C3H/He Slc (C3H; H-2k, Mls-1b) mice were primed i.v. with 1 x 10(8) viable spleen cells from H-2-identical AKR/J Sea (AKR; H-2k, Mls-1a) mice and treated with 200 mg/kg of CY 2 days later, a long-lasting skin allograft tolerance to AKR was established. When [C57BL/6 Sea (B6; H-2b, Mls-1b) x AKR]F1 (B6AKF1) cells were used as the tolerogen, however, only a moderate, but not long-lasting, skin tolerance to AKR was observed. In the C3H mice treated with AKR cells and CY, the intrathymic clonal deletion of V beta 6+ T cells, which are strongly correlated with reactivity to Mls-1a antigens, was observed in the chimeric thymus on day 35, although neither the clonal deletion of V beta 6-bearing T cells nor the mixed chimerism was observed in the thymus on day 14. In the C3H mice treated with B6AFKF1 cells followed by CY, however, neither the clonal deletion of V beta 6+ T cells nor the mixed chimerism was observed in the thymus throughout the test period. In the lymph nodes of the C3H mice treated with AKR cells and CY, only CD4+ V beta 6+ T cells, bur not CD8+V beta 6+ T cells, had selectively decreased by day 14, and they were hardly detectable on day 35. The selective decrease of CD4+V beta 6+ T cells in the lymph nodes was also observed by day 14 when B6AKF1 cells were used as the tolerogen, although CD4+V beta 6+ T cells gradually increased on day 35, at which time almost all skin grafts from AKR had already been rejected. These results strongly support the necessity of the intrathymic mixed chimerism and clonal deletion of donor-reactive T cells for a long-lasting skin allograft tolerance in CY-induced tolerance.

In vitro and in vivo analysis of bone marrow-derived CD3+, CD4-, CD8-, NK1.1+ cell lines

The development of methods of avoiding graft-versus-host disease (GVHD) while retaining the alloengraftment-promoting and anti-leukemic effects of allogeneic T cells is a major goal of research in bone marrow transplantation (BMT). We have recently obtained evidence suggesting that natural suppressor (NS) cells derived from T cell-depleted (TCD) syngeneic marrow can protect against GVHD while permitting alloengraftment. We have now attempted to enrich and then propagate NS cells in vitro, with the goal of obtaining an enhanced anti-GVHD effect by adoptive transfer in vivo. Two long-term cell lines were generated culturing BMC depleted of Mac1-positive cells and of Mac1-positive plus Thy1-positive cells in high concentrations of IL-2. Both cell lines showed anti-GVHD effects when administered along with a GVHD-producing inoculum, while permitting complete allogeneic reconstitution. A clone derived from Mac1-depleted BMC protected completely against a more chronic pattern of GVHD. These cell lines demonstrated suppressive activity in vitro, cytolytic activity against a broad range of natural killer (NK)-sensitive and NK-resistant targets, and a novel cell surface phenotype, with characteristics of both alpha beta-TcR-bearing T cells and of NK cells. In some respects, these cells resemble LAK cells and differ from fresh NS cells, and from the cloned NS cells derived from spleens of total lymphoid irradiation (TLI)-treated mice and neonatal mice. To our knowledge, this is the first detailed phenotypic analysis of cell lines with in vivo anti-GVHD activity. If applicability can be demonstrated in large animal models, the ability to use bone marrow as a source of such protective cell lines might also have potential utility in clinical BMT.

Distinct sequence of negative or positive selection implied by thymocyte T-cell receptor densities

Recent evidence suggests that positive and negative selection of thymocytes bearing alpha beta T-cell receptors occurs during the predominant double-positive (CD4+CD8+) stage. But the sequence or stage at which positive or negative selection occurs during thymocyte maturation has not been well defined. Here we use transgenic mice to show that the CD4+CD8+ stage might be further subdivided into CD3lo (low) and CD3in (intermediate) stages. The CD3in stage could represent T cells that have been positively selected, as this stage is dependent on the presence of the appropriate major histocompatibility complex restriction element. In addition, we use two different tolerizing antigens to show that negative selection may occur either before or after this CD3in stage.

Viral escape by selection of cytotoxic T cell-resistant virus variants in vivo

Viruses persist in an immune population, as in the case of influenza, or in an individual, as postulated for human immunodeficiency virus, when they are able to escape existent neutralizing antibody responses by changing their antigens. It is now shown that viruses can in principle escape the immunosurveillance of virus-specific cytotoxic T cells by mutations that alter the relevant T-cell epitope.

The presumptive CDR3 regions of both T cell receptor alpha and beta chains determine T cell specificity for myoglobin peptides

The T cell receptor alpha/beta (TCR-alpha/beta) is encoded by variable (V), diversity (D), joining (J), and constant (C) segments assembled by recombination during thymocyte maturation to produce a heterodimer that imparts antigenic specificity to the T cell. Unlike immunoglobulins (Igs), which bind free antigen, the ligands of TCR-alpha/beta are cell surface complexes of intracellularly degraded antigens (i.e., peptides) bound to and presented by polymorphic products of the major histocompatibility complex (MHC). Therefore, antigen recognition by T cells is defined as MHC restricted. A model has been formulated based upon the similarity between TCR-alpha/beta V region and Ig Fab amino acid sequences, and the crystal structure of the MHC class I and Ig molecules. This model predicts that the complementarity determining regions (CDR) 1 and 2, composed of TCR V alpha and V beta segments, primarily contact residues of the MHC alpha helices, whereas V/J alpha and V/D/J beta junctional regions (the CDR3 equivalent) contact the peptide in the MHC binding groove. Because polymorphism in MHC proteins is limited relative to the enormous diversity of antigenic peptides, the TCR may have evolved to position the highly diverse junctional residues (CDR3), where they have maximal contact with antigen bound in the MHC peptide groove. Here, we demonstrate a definitive association between CDR3 sequences in both TCR alpha and beta chains, and differences in recognition of antigen fine specificity using a panel of I-Ed-restricted, myoglobin-reactive T cell clones. Acquisition of these data relied in part upon a modification of the polymerase chain reaction that uses a degenerate, consensus primer to amplify TCR alpha chains without foreknowledge of the V alpha segments they utilize.

T cell receptor V beta genes expressed by IgG anti-DNA autoantibody-inducing T cells in lupus nephritis: forbidden receptors and double-negative T cells

In the (SWR x NZB)F1 (SNF1) model of lupus nephritis, pathogenic variety of IgG anti-DNA autoantibodies are induced by certain T helper (Th) cells that are either CD4+ or CD4-CD8- (double negative; DN) in phenotype. From the spleens of eight SNF1 mice with lupus nephritis, 149 T cell lines were derived and out of these only 25 lines (approximately 17%) were capable of augmenting the production of pathogenic anti-DNA autoantibodies. Herein, we analyzed the T cell receptor (TcR) V beta genes used by 16 such pathogenic autoantibody-inducing Th cell lines. Twelve of the Th lines were CD4+ and among these five lines expressed V beta 8 (8.2 or 8.3). The V beta 8 gene family is contributed by the NZB parent to the SNF1 mice, since it is absent in the SWR parental strain. Three other CD4+ Th lines expressed V beta 4, another was V beta 2+ and one line with poor autoantibody-inducing capability expressed V beta 1. Four autoantibody-inducing Th lines from the SNF1 mice had a DN phenotype and these lines were also autoreactive, proliferating in response to syngeneic spleen cells. Among these DN Th lines, two expressed V beta 6 and one expressed V beta 8.1 TcR. Both of these are forbidden TcR directed against Mls-1a (Mlsa) autoantigens expressed by the SNF1 mice and such autoreactive T cells should have been deleted during thymic ontogeny. Thus, the DN Th cells of non-lpr SNF1 mice are different from the DN cells or MRL-lpr which lack helper activity and do not express forbidden TcR. The spleens of 6 out of 19 nephritic SNF1 animals tested also showed an expansion of forbidden autoreactive TcR+ cells that were mainly DN. Two of these animals expressed high levels of V beta 6 (anti-Mlsa) and V beta 11 (anti-I-E) TcR+ cells, three others had high levels of V beta 11+ cells alone and one animal had an expanded population of V beta 17a+ (anti-I-E) cells. The I-E-reactive TcR again should have been eliminated in the SNF1 thymus, since they express I-E molecules contributed by the NZB parent. The SWR parents of SNF1, are I-E-; moreover, they lack the V beta 11 gene but they express V beta 17a in peripheral T cells. Whereas the NZB parents are I-E+, they lack a functional V beta 17a gene and they delete mature V beta 11+ T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of the region of T cell receptor beta chain that interacts with the self-superantigen MIs-1a

Superantigen-MHC complexes are known to stimulate T cells primarily via the V beta element of the T cell receptor. In this paper we identify a number of amino acid residues that define the region of a particular V beta element interacting with one of the self-superantigens, MIs-1a. These residues are predicted to lie on a beta-pleated sheet of the T cell receptor, away from the complementarity determining regions of the receptor, which are thought to interact with complexes of conventional peptide antigens and MHC. In support of this prediction, mutations affecting MIs-1a activity have no effect on the response to conventional antigen and MHC.

A role for clonal inactivation in T cell tolerance to Mls-1a

Clonal deletion plays a major part in the maintenance of natural self-tolerance in both normal and transgenic mice. Self antigens that are expressed in the thymus result in the physical elimination of autoreactive thymocytes at a particular stage in their development. For example, the majority V beta 6- and V beta 8.1-bearing T cells that recognize the minor lymphocyte-stimulating antigen, Mls-1a (ref. 10) , are clonally deleted in the thymuses of normal mice and transgenic mice expressing Mls-1a (refs 2, 3, 9). In contrast, a very different mechanism of tolerance involving the functional inactivation, but not elimination, of autoreactive cells, termed clonal inactivation or clonal anergy, has been implicated in some experimentally manipulated systems of tolerance. To test further the mechanisms involved in self-tolerance, we have generated transgenic mice expressing a V beta 8.1 beta chain on greater than 95% of peripheral T cells and have tested tolerance to Mls-1a in these mice. Surprisingly, a significant fraction of the CD4+ peripheral cells that survived deletion were non-responsive in vitro to any stimulus tested. Naturally occurring tolerance to a self antigen expressed in the thymus can thus be mediated by clonal anergy, as well as by clonal deletion.

Analysis of T cell receptor V beta gene usage in primary mixed lymphocyte reactions: evidence for directive usage by different antigen-presenting cells and Mls-like determinants on T cell blasts

The usage of four different T cell receptor (TcR) V beta gene families within normal, non-primed T cell populations in response to various types of antigen-presenting cells (APC) in primary mixed lymphocyte reaction has been studied. We demonstrate that distinct patterns of V beta gene usage are obtained within a given T cell population in response to different types of APC with the same allo-H-2. When responder T cells are stimulated with one type of allogeneic APC, from various H-2-disparate mice, the same V beta gene preference is observed. Furthermore, when H-2- and Mls-mismatched APC gene used as stimulators, the Mls-associated V beta 6 and V beta 8.1 gene families are highly elevated in response to both B and T cell blasts from certain Mls-positive strains. The results demonstrate that different types of allogeneic APC have the capacity to generate biases in TcR V beta gene usage and imply that functional Mls-like determinants are presented by T cell blasts. The findings are discussed with respect to TcR-major histocompatibility complex interactions in allostimulation.

Sequential analysis of distributions of donor-derived thymocytes bearing T-cell antigen receptor (TCR) and donor-derived Ia+ cells in thymuses of fully allogeneic bone marrow chimera in mice

Lethally irradiated SJL/J mice were reconstituted with B10 bone marrow cells, and the process of thymic reconstitution by donor-derived cells positive for I-A or V beta 8 molecules was investigated. The donor-derived Ia+ cells appeared in the medulla on day 7 after reconstitution. The Ia+ cells became confluent up to day 14, and the cellularity in the medulla on day 17 was almost the same as that in the normal thymus. Dull V beta 8+ thymocytes were first recognized in the cortex on day 10 and were identifiable in the medulla by day 14. The V beta 8+ cells seemed to be mainly CD4+8+ double-positive. Furthermore, most of the V beta 8+ cells in the medulla of chimeras given cyclosporin A for 3 weeks after reconstitution appeared to be CD4+8+ thymocytes which bear a low concentration of TCR exist in the thymic medulla at a relatively early stage when donor-derived Ia+ cells have already settled there. The coincidental appearance and coexistence of Ia+ cells and TCR+ thymocytes in the medulla suggest that these histological characteristics may be related to the selection of thymocytes in this area.

Clonal deletion: a mechanism of tolerance in mixed bone marrow chimeras

The mechanism of antigen-specific immunologic unresponsiveness which results from lethal irradiation and mixed (syngeneic-allogeneic) bone marrow cell (BMC) reconstitution is unknown. To determine whether clonal deletion is the mechanism of tolerance in this model, monoclonal antibody (Mab) RR-4-4, specific for a T-cell receptor (V beta 6) reactive against the minor alloantigen MLsa, was employed. Six-week-old B10 mice (H-2b, Mlsb, Thyl.2) were tolerized to AKR antigens (H-2k, Mlsa, Thyl.1) by whole body irradiation (950 R) and iv infusion of T-cell-depleted (TCD) B10 BMC + non-TCD AKR BMC. Chimerism and antigen-specific tolerance were documented by flow microfluorometry (FMF), skin grafting, mixed lymphocyte reaction, and cell-mediated lympholysis. When tolerant B10 mice (n = 15) had accepted AKR skin grafts for greater than 100 days, these animals were studied for the presence of host V beta 6+ T cells using Mab RR-4-4. FMF revealed that 0-5% of host (B10) lymph node and spleen cells from chimeras were V beta 6+ while 15-20% of lymph node and spleen cells from control B10 mice expressed V beta 6. These data demonstrate that clonal deletion occurs in the lethal irradiation-mixed reconstitution model as evidenced by the near total elimination of Mlsa-reactive V beta 6+ T cells and suggest that it maybe a mechanism responsible for tolerance in adult mice.

Establishment and characterization of a leukemic murine cell line derived from MCF 247 MuLV-induced T-cell lymphoma

Understanding of the leukemic evolution of human non-Hodgkin's lymphomas is hindered by the lack of appropriate animal models. For this purpose, a highly leukemic cell line NQ22, derived from a MCF 247 murine leukemia virus (MuLV)-induced murine T-cell lymphoma, was established, and its preliminary characterization is described. The NQ22 cell line is easily transplantable subcutaneously (s.c.) into syngeneic AKR mice exhibiting early peripheral blood invasion and widespread dissemination with a leukemic pattern of infiltration. Such peculiar in vivo behavior is a stable phenotypic feature, probably determined genetically. Biological and differentiation characteristics of the NQ22 cell line were analyzed and compared to those of other non-leukemic T-lymphoma lines. In addition, no evidence of possible involvement of plasminogen activator (PA) enzymes and of their inhibitors (PAI) in the spreading ability of NQ22 cells was observed.

Flexibility of the T cell repertoire. Self tolerance causes a shift of T cell receptor gene usage in response to insulin

Bovine insulin(BI)-specific I-Ab-restricted T cell clones have been characterized for fine specificity and TCR gene usage. We have demonstrated that mouse strains carrying H-2b on three different genetic backgrounds (C57BL, BALB, and 129) rearrange and express the V beta 6 gene in a large proportion (36%) of insulin-specific clones. In these strains, the non-MHC background did not seem to influence TCR gene usage in response to BI. The V beta 6+ clones appeared to be selected by the antigen. In contrast, no V beta 6+ clones could be isolated from (B6 x DBA/2)F1 mice, where V beta 6+ (and V beta 8.1+) T cells are deleted by self tolerance to Mls-1a. Thus, although a small proportion of residual V beta 6+ cells had been demonstrated in Mls-1a mice, these cells could not be retrieved in a response that uses V beta 6 predominantly. In functional terms, therefore, the deletion of V beta 6 by self tolerance appears to be complete. Instead of V beta 6, the majority (up to 60%) of I-Ab- as well as I-Ad-restricted insulin-specific clones from the (B6 x DBA/2)F1 mice expressed V beta 8.2 and V beta 8.3. This shift of gene usage was not accompanied by any detectable change in the fine specificity pattern of response. Thus, in the insulin-specific response, the flexibility of T cell repertoire fully compensates for deletions caused by self tolerance.

Correlation between the V beta 4+ CD8+ T-cell population and the H-2d haplotype

The V beta 4+ T-cell population was examined with a newly established antibody, KT4, specific for V beta 4. Between 4.8% and 19.4% of CD3+ peripheral T cells from various inbred strains of mice or F1 hybrids expressed V beta 4. The CD4 T-cell population had higher numbers of V beta 4+ T cells (5.5%-20.6%) than the CD8 T-cell population (2.5%-10.7%). Deletion of certain V beta-expressing T cells due to the presence of the Mlsa antigen and/or the absence of certain Tcrb-V genes increased relative numbers of V beta 4+ T cells. The data suggest that V beta 4+ CD8+ T cells might be positively selected by H-2d molecules.

In vivo elimination of T cells expressing specific T-cell receptor V beta chains in mice susceptible to collagen-induced arthritis

Type II collagen-induced arthritis (CIA) is believed to be dependent on T cells expressing a limited number of V beta chains. Two different methods were used to selectively eliminate T cells expressing a certain T-cell receptor (TcR) V beta chain in mouse strains susceptible to CIA. In vivo treatment with monoclonal anti-V beta 6 or anti-V beta 8.1,2 antibodies did not alter CIA, despite a reduction of the major part of the V beta 6+ or V beta 8.1,2+ lymph node cells (LNC), as measured by flow cytometric (FACS) analyses. The reduction was not due to complete elimination of V beta 6+ or V beta 8.1,2+ cells, since part of the V beta 6 and V beta 8.1,2 expressing cells returned later, even in mice that had been thymectomized first to prevent maturation of new T cells. In contrast, treatment with antibodies against CD4 efficiently abrogated development of CIA. In the (CBA x DBA/1J)F1 and the (BALB/c x DBA/1J)F1 mice, where M1s1a was combined with expression of I-E, the V beta 6+ LNC were deleted. In spite of the deletion, both F1 strains were highly susceptible to CIA.

Strong T cell tolerance in parent----F1 bone marrow chimeras prepared with supralethal irradiation. Evidence for clonal deletion and anergy

T cell tolerance induction was examined in long-term H-2-heterozygous parent----F1 chimeras prepared with supralethal irradiation (1,300 rad). Although these chimeras appeared to be devoid of host-type APC, the donor T cells developing in the chimeras showed marked tolerance to host-type H-2 determinants. Tolerance to the host appeared to be virtually complete in four assay systems: (a) primary mixed lymphocyte reactions (MLR) of purified lymph node (LN) CD8+ cells (+/- IL-2); (b) primary MLR of CD4+ (CD8-) thymocytes; (c) skin graft rejection; and (d) induction of lethal graft-vs.-host disease by CD4+ cells. Similar tolerance was observed in chimeras given double irradiation. The only assay in which the chimera T cells failed to show near-total tolerance to the host was the primary MLR of post-thymic CD4+ cells. In this assay, LN CD4+ cells regularly gave a significant antihost MLR. The magnitude of this response was two- to fourfold less than the response of normal parental strain CD4+ cells and, in I-E(-)----I-E+ chimeras, was paralleled by approximately 70% deletion of V beta 11+ cells. Since marked tolerance was evident at the level of mature thymocytes, tolerance induction in the chimeras presumably occurred in the thymus itself. The failure to detect host APC in the thymus implies that tolerance reflected contact with thymic epithelial cells (and/or other non-BM-derived cells in the thymus). To account for the residual host reactivity of LN CD4+ cells and the incomplete deletion of V beta 11+ cells, it is suggested that T cell contact with thymic epithelial cells induced clonal deletion of most of the host-reactive T cells but spared a proportion of these cells (possibly low affinity cells). Since these latter cells appeared to be functionally inert in the thymus (in contrast to LN), we suggest that the thymic epithelial cells induced a temporary form of anergy in the remaining host-reactive thymocytes. This anergic state disappeared when the T cells left the thymus and reached LN.

Characterization of V beta-bearing cells in athymic (nu/nu) mice suggests an extrathymic pathway for T cell differentiation

In the present article, the expression of the T cell receptor (TcR) beta chain and other T cell molecules was evaluated in surface immunoglobulin-negative spleen cell populations of young and old BALB/c and C57BL/6 nude mice, using a panel of monoclonal antibodies. The results obtained show that in young nude mice, most Thy-1high cells do not express other T cell markers. These mice have, however, a sizable population of Thy-1low cells with the same phenotype of alpha/beta+, CD4-CD8- thymocytes or MRL/lpr peripheral T cells, expressing predominantly genes of the V beta 8 family. The evolution of alpha/beta+ cells in aging nudes is strongly suggestive of an extrathymic pathway of differentiation of these cells since (a) the acquisition of high density TcR and CD3, as well as Thy-1 or CD4CD8 antigens at the cell surface of nude V beta+ T cells is not simultaneous; (b) alpha/beta+ cells in nude mice co-express other T cell markers at random and, even in old mice, they never completely resemble to the predominant high Thy-1+ CD3+ TcR alpha/beta+, CD4+CD8+ cells of euthymic controls; and (c) BALB/c nude T cells express V beta 11 genes, that are deleted in euthymic BALB/c mice. This latter finding may also indicate differences in the mechanisms of selection of T cells specificities in the thymus vs. the peripheral pools.

Thymic epithelium tolerizes for histocompatibility antigens

The role of thymic epithelium in the establishment of tissue tolerance was analyzed with a murine chimeric system. All T cells differentiated from birth onward in a thymus comprising allogeneic epithelium and syngeneic hematopoietic cells. Embryonic thymic rudiments that contained no hematopoietic cells from C3H (H-2k) donors were grafted to newborn athymic (nude) BALB/c (H-2d) mice. Chimeras that had normal T cell numbers and function rejected third-party skin grafts, but permanently accepted grafts syngeneic to the thymic epithelium. In vitro functional assays did not always correlate with the state of tolerance in vivo. Thus, pure thymic epithelium induces tolerance to histocompatibility antigens.

Thymic epithelium tolerizes for histocompatibility antigens

The role of thymic epithelium in the establishment of tissue tolerance was analyzed with a murine chimeric system. All T cells differentiated from birth onward in a thymus comprising allogeneic epithelium and syngeneic hematopoietic cells. Embryonic thymic rudiments that contained no hematopoietic cells from C3H (H-2k) donors were grafted to newborn athymic (nude) BALB/c (H-2d) mice. Chimeras that had normal T cell numbers and function rejected third-party skin grafts, but permanently accepted grafts syngeneic to the thymic epithelium. In vitro functional assays did not always correlate with the state of tolerance in vivo. Thus, pure thymic epithelium induces tolerance to histocompatibility antigens.

Preferential usage of V alpha 4 and V beta 10 T cell receptor genes by lymphocytic choriomeningitis virus glycoprotein-specific H-2Db-restricted cytotoxic T cells

Correlations between the T cell receptor (TcR) V gene usage and the specificity of T cells have been primarily described for major histocompatibility complex (MHC) class II-restricted helper T cell responses. In the present study the TcR genes expressed by MHC class I-restricted murine cytotoxic T cells (CTL) specific for a major epitope of the lymphocytic choriomeningitis virus (LCMV), LCMV-GP2(275-289), were investigated. The TcR primary structure of an LCMV-GP2(275-289) specific H-2Db-restricted CTL clone has been determined. It uses a member of the V alpha 4 family joined to J alpha AN14.4 for the alpha chain and V beta 10 rearranged to D beta 2.1 and J beta 2.4 for its beta chain. Four other independent LCMV-GP2(275-289) specific H-2Db-restricted CTL clones also expressed V alpha 4 and V beta 10 gene elements. Furthermore, V alpha 4 and V beta 10 were preferentially expressed by polyclonal CTL of C57BL/6 origin specific for LCMV. These results suggest that both TcR V alpha and V beta regions are important for the recognition of the LCMV-GP2(275-289) epitope on H-2Db molecules.

Early induction of anti-double-stranded DNA antibodies in lupus-prone MRL mice inoculated with Ly-24+ cells cloned from lymph node cells of an MRL/Mp-lpr/lpr mouse: possible effect of putative cytokines produced by cloned Ly-24+ cells

We have reported that a cell line, KML1, obtained from lymph node cells of a 16-week-old female MRL/Mp-lpr/lpr (MRL/1) mouse produces a soluble factor(s) that promotes formation of anti-single-stranded (ss) DNA antibodies by cultures of spleen cells from old MRL/l mice (greater than 16 weeks old). Detailed examination revealed that KML1-7 cells cloned from the cell line KML1 were only positive for the Lys-24 (Pgp-1) phenotype, and were negative for other typical phenotypes tested, such as Thy-1, Ly-1, Ly-2, Ly-4 (L3T4) and Ly-5 (B220). This finding suggested that this line was of prothymocyte or myeloid cell lineage. From day 70 after subcutaneous inoculation of KML1-7 cells into 10-week-old MRL/Mp(-)+/+(MRL/n) mice, IgG anti-dsDNA antibodies began to replace IgM anti-dsDNA antibodies in the serum of these mice, but anticardiolipin, anti-trinitrophenyl hapten (TNP) and anti-poly(ADP-ribose) antibodies did not increase significantly. The predominant subclasses of anti-dsDNA antibodies that increased were IgG2a and IgG2b. IgG anti-dsDNA antibodies also became detectable as early as day 22 after inoculation of KML1-7 cells into MRL/l mice of 10 weeks old. The finding that in MRL/n mice the IgM isotype was increased first and was soon replaced by the IgG isotype was consistent with findings when spleen cells from MRL/n mice of 20 weeks old primed with ssDNA were cultured in the presence of conditioned medium containing a putative cytokine(s) (PC) produced by KML1-7 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed death of autoreactive thymocytes

T lymphocytes bearing high-affinity T-cell receptors (TCR) for self-antigens are clonally deleted during thymus development. Several recent studies have identified variable domains of the beta-chain of the TCR that are specifically deleted in vivo in mouse strains that express major histocompatibility complex class II molecules in addition to poorly defined self-antigens, including those encoded by the Mls-1a and Mls-2a loci. Deletion of autoreactive cells in these systems occurs in the thymus, and antibody blocking experiments in vivo have implicated the phenotypically immature CD4+CD8+ 'cortical' subset as the target population for clonal deletion. Similarly, studies with transgenic mice bearing autoreactive TCR have provided independent evidence that clonal deletion occurs at the CD4+CD8+ stage of development. But none of these studies directly identified dying autoreactive cells, and the circumstances leading to deletion remain unclear. Here we report that neonatal thymus contains a significant population of phenotypically mature CD4+CD8- cells bearing autoreactive TCR. When placed in short-term culture, a large proportion (60%) of these autoreactive cells die selectively. Furthermore, their death can be prevented by inhibitors of macromolecule (RNA and protein) synthesis, as is the case for glucocorticoid-induced death of thymocytes. These data indicate that physiological clonal deletion of autoreactive cells involves 'programmed' cell death, and that it can occur in cells with a mature (CD4+CD8-) surface phenotype.

T cell receptor (TcR) beta chain transgenic mice: studies on allelic exclusion and on the TcR+ gamma/delta population

To study allelic exclusion of TcR genes we analyzed two types (I and II) of TcR beta transgenic mice. T cells derived from both types of mice contained similar amounts of transgenic RNA transcripts; however, surface expression of the transgenic beta chain was drastically reduced in type II compared to type I. In type I transgenic mice, productive rearrangements and expression of endogenous TcR beta genes were suppressed whereas on T cells of type II mice, both transgenic and endogenous TcR beta chains were expressed on the surface of the same cell. These findings suggest that allelic exclusion of TcR genes in beta transgenic mice depends on amount and/or onset of transgene expression during thymic development. Furthermore, TcR gamma rearrangements and the population of TcR gamma/delta-bearing double-negative CD4-CD8- thymocytes were reduced fivefold in type I transgenic animals. However, the V gamma usage and the gamma/delta+ dendritic epidermal cell populations appeared normal. RNase protection analysis further revealed low levels of transgenic TcR beta chain transcripts in TcR+ gamma/delta CD4-CD8- thymocytes. These results suggest that the beta transgene only quantitatively influences the gamma/delta T cell compartment, and supports the independence of the gamma/delta population.

Phenotype of intraepithelial lymphocytes in euthymic and athymic mice: implications for differentiation of cells bearing a CD3-associated gamma delta T cell receptor

This study was carried out to determine the exact phenotype of intraepithelial lymphocytes (IEL) in euthymic and athymic nude mice. The phenotype of IEL in euthymic and athymic mice is mainly CD3+CD8+. However, based on Thy-1- and CD3-associated receptor expression we can subdivide the CD3CD8 population into different subpopulations in euthymic and athymic mice. In euthymic and athymic mice several CD3CD8 populations can be defined. One population expressing Thy-1 and the T cell receptor (TcR) alpha beta is absent in athymic mice. Two other CD3+CD8+ populations can be detected in euthymic and athymic mice. Based on Northern blot and flow cytometric analysis we have to conclude that these populations express the CD3-associated TcR gamma delta. One of the TcR gamma delta-expressing populations also expresses Thy-1 at low surface density. This is in contrast to the CD3CD8 population expressing the TcR alpha beta, which expresses Thy-1 at high surface density. There are also, however, especially in athymic nude mice, significant numbers of CD3-CD8+ cells present with the same localization as IEL. The function of these cells is yet unknown. Using a probe for the delta chain we have shown that IEL preferentially express 2-kb mRNA, while nearly no delta chain 1.7-kb mRNA is expressed by these cells. This is in contrast to delta mRNA in thymocytes. Equal quantities of the 1.7- and 2.0-kb delta chain mRNA species were found in RNA isolated from thymocytes. The results imply that CD3+CD8+ intestinal IEL expressing the CD3-associated TcR gamma delta can differentiate in absence of the thymus and represent a thymus-independent lineage of cells bearing this receptor.

Intrathymic clonal deletion of V beta 6+ T cells in cyclophosphamide-induced tolerance to H-2-compatible, Mls-disparate antigens

When C3H (H-2k, Mls-1b) mice were primed intravenously with 10(8) viable spleen cells from AKR (H-2k, Mls-1a) and treated intraperitoneally with 200 mg/kg of cyclophosphamide (CP) 2 d later, not only a long-lasting skin allograft tolerance but also a tolerance in mixed lymphocyte reaction to Mls-1a-encoded antigens was established. The cellular mechanisms of CP-induced tolerance were examined by assessing the V beta 6-bearing T cells that are strongly correlated with reactivity to Mls-1a-encoded antigens bound to MHC class II molecules. At the relatively early stage (2 or 5 wk) after the CP treatment, CD4+-V beta 6+ T cells of C3H origin were preferentially eliminated in the lymph nodes of the tolerant mice, whereas CD8+-V beta 6+ T cells remained. On the other hand, neither CD4+CD8- nor CD4-CD8+ thymocytes bearing a high density of V beta 6 was detected in the chimeric thymus. Namely, in the thymus of the tolerant C3H mice, neither mixed chimerism nor the clonal deletion of the V beta 6-bearing T cells was observed on day 14, whereas both of them were observed on day 35. The clonal deletion and mixed chimerism in the thymus were lasting for greater than 10 wk after the CP treatment. Expression of V beta 6 on the peripheral T cells in the tolerant C3H mice gradually reduced in the process of time. These results strongly suggested that the clonal deletion in the thymus was one of the essential mechanisms in the CP-induced tolerance system.

The surface of dendritic cells in the mouse as studied with monoclonal antibodies

A family of dendritic cells has been identified in situ and in vitro by microscopy and immunolabeling. The members of this family include the dendritic cells isolated from lymphoid organs, Langerhans cells [LC] of the epidermis, veiled cells in afferent lymph, and interdigitating cells [IDC] in the T-cell areas. Some common features to all members of the family are high levels of MHC class II antigens, a lack of most B and T cell markers, and an absence or low levels of macrophage/granulocyte antigens. This review summarizes the markers of mouse dendritic cells as assessed by a panel of monoclonal antibodies, and stresses a few recent findings. 1) In spleen, there are two populations of dendritic cells. More than 75% of isolated cells are 33D1+, NLDC145-, and J11d-, while the remainder have the reciprocal phenotype and thus share the NLDC145 antigen of IDC. Thymic dendritic cells, released by collagenase digestion, and epidermal LC also are 33D1-, NLDC145+, J11d+. 2) When epidermal LC are placed in culture, there are changes in cell function and phenotype. There is a decrease in Fc gamma receptors and the F4/80 macrophage antigen, an increase in class I and II MHC products and p55 IL-2 receptors, and persistence of the NLDC145 IDC antigen. The cultured LC thereby resembles the IDC. 3) A new antibody N418 shows that dendritic cells express the p150/90 member of the leukocyte beta 2 integrin family. Immunolabeling of tissue sections of spleen indicates that N418+ dendritic cells not only are present in the periarterial sheaths, the location of IDC, but also in "nests" at the periphery of the T area where 33D1 has been found. The peripheral collections interrupt the marginal zone of macrophages that separates white and red pulp, and places the dendritic cells in the path of T cells as they move through the white pulp. Therefore the members of the dendritic cell family have important markers in common, as well as differences that are associated with state of immunologic function and location.

Surprisingly uneven distribution of the T cell receptor V beta repertoire in wild mice

We have examined TCR V beta expression in a collection of wild mice. Many of the mice were homozygous for a large deletion at the V beta locus, and many animals also suppressed expression of several V betas using self superantigens. Expression of V beta 8.2 was unexpectedly suppressed by a self superantigen in some wild mice, which was due to the presence in these animals of a variant V beta 8.2 gene. The amino acid changes in this gene product suggest contact sites between V beta and the superantigen. Although all V betas are expressed within each wild mouse population, individual mice have a limited and variable V beta repertoire. The independent origin of multiple V beta deletions and the presence of polymorphic self superantigens suggest that this variation may be maintained by balancing selection.

Production and characterization of a rat monoclonal antibody against the murine CD3 molecular complex

We describe the production of a rat monoclonal antibody, 17A2, that detects the T cell receptor-associated CD3 molecular complex. 17A2 cross-competes with a CD3 epsilon-specific reagent and similarly stimulates IL-2 production by T cells. Immunohistological and cell separation applications are shown.

Tolerance induction in double specific T-cell receptor transgenic mice varies with antigen

The crucial role of the thymus in immunological tolerance has been demonstrated by establishing that T cells are positively selected to express a specificity for self major histocompatibility complex (MHC), and that those T cells bearing receptors potentially reactive to self antigen fragments, presumably presented by thymic MHC, are selected against. The precise mechanism by which tolerance is induced and the stage of T-cell development at which it occurs are not known. We have now studied T-cell tolerance in transgenic mice expressing a T-cell receptor with double specificities for lymphocytic choriomeningitis virus (LCMV)-H-2Db and for the mixed-lymphocyte stimulatory (MIsa) antigen. We report that alpha beta TCR transgenic mice tolerant to LCMV have drastically reduced numbers of CD4+CD8+ thymocytes and of peripheral T cells carrying the CD8 antigen. By contrast, tolerance to MIsa antigen in the same alpha beta TCR transgenic MIsa mice leads to deletion of only mature thymocytes and peripheral T cells and does not affect CD4+CD8+ thymocytes. Thus the same transgenic TCR-expressing T cells may be tolerized at different stages of their maturation and at different locations in the thymus depending on the antigen involved.

Failure of T cell receptor V beta negative selection in an athymic environment

The mature T cell receptor (TCR) repertoire is the result of selection events during T cell development. Previous assessment of TCR beta-chain selection with serologic and molecular probes demonstrated both positive and negative selection. Although this work suggested a critical role for the thymus, no direct assessment has been made of the requirement for a thymus in TCR V beta selection. A comparison of TCR V beta expression in four different congenic pairs of normal and nu/nu (athymic) mice indicated that the normal V beta deletions associated with tolerance to self minor lymphocyte stimulating (Mlsc) antigens or to self major histocompatibility complex (MHC)-encoded E alpha E beta products did not occur in most athymic mice. Thus, the thymus has a critical role in mediating self tolerance by negative selection.

Thymic requirement for clonal deletion during T cell development

During T cell differentiation, self tolerance is established in part by the deletion of self-reactive T cells within the thymus (negative selection). The presence of T cell receptor (TCR)-alpha beta + T cells in older athymic (nu/nu) mice indicates that some T cells can also mature without thymic influence. Therefore, to determine whether the thymus is required for negative selection, TCR V beta expression was compared in athymic nu/nu mice and their congenic normal littermates. T cells expressing V beta 3 proteins are specific for minor lymphocyte stimulatory (Mlsc) determinants and are deleted intrathymically due to self tolerance in Mlsc+ mouse strains. Here it is shown that V beta 3+ T cells are deleted in Mlsc+ BALB/c nu/+ mice, but not in their BALB/c nu/nu littermates. Thus, the thymus is required for clonal deletion during T cell development.

In vivo T cell tumor therapy with monoclonal antibody directed to the V beta chain of T cell antigen receptor

To test whether antibodies directed to TCR affect T cell tumor growth in vivo, mice were inoculated intravenously with C6VL tumor cells expressing V beta 6 TCR and then treated intraperitoneally with mAb specific for V beta 6 TCR. Administration of anti-V beta 6 antibody prolonged survival of mice bearing V beta 6-expressing tumor cells and it led to the induction of host immunity to the tumor cells in surviving animals. This treatment eliminated not only tumor cells bearing V beta 6 TCR but also normal host T cells expressing V beta 6 T cells receptors. However, the lack of V beta 6-expressing T cells in such treated mice did not result in generalized immune disfunction. These data demonstrate the utility of anti-TCR V segment antibody in the treatment of T cell tumors. Most importantly, since the number of V genes for the T cell antigen receptor is limited, both in man and in mouse, it should be possible to establish a panel of mAbs directed to each V gene product and use such antibodies in the treatment of T cell neoplasms.

Extra-thymic immature T cells: development in polyoma virus-induced murine salivary gland tumors

Lymphocyte infiltrates which occur in some polyoma virus-induced murine salivary epithelial tumors are characterized. The lymphocytic infiltrates within the salivary tumors resemble cortical thymocytes with the phenotype PNA+, Thy-1.2 bright, Ly-2+L3T4+, Ly-1 dim, H-2Kdim, KJ16-133-. The salivary lymphocytes showed proliferation based on analysis of RNA and DNA content. Because thymocytes lose the immature phenotype before leaving the thymus, we propose that the salivary tumor infiltrates result from the intra-tumoral differentiation of blood-derived prothymocytes into "cortical thymocytes". Histologic examination of the salivary tumors indicates expression of class II major histocompatibility antigen on the tumor epithelium which may be essential in establishing the extra-thymic T lymphocyte-inductive microenvironment within the tumor.

Primary polyoma virus-induced murine thymic epithelial tumors. A tumor model of thymus physiology

Thymic tumors were induced in C3'/Bittner mice by neonatal inoculation with polyoma virus. The objective of this study was to identify the phenotypes of the cells within the tumors and to attempt to determine the origin of the neoplastic cell population(s). At the ultrastructural level, the neoplastic cells resembled normal thymic epithelium with tonofilaments and desmosomes. Immunoperoxidase staining demonstrated the presence of cytokeratin, Iak, -beta 2-microglobulin, -asialo-GM1, the thymic cortical epithelial marker ER-TR4, and the medullary epithelial marker ER-TR5. Islands of normal cortical thymocytes supported by residual normal cortical epithelium and acid phosphatase-positive cortical macrophages were interspersed in the tumors. Residual islands of normal medullary architecture with nonspecific esterase-positive IDCs were rarely identified in tumors. Most lymphocytes in the tumors were normal immature cortical thymocytes with the phenotype Tdt+, PNA+, Thy 1.2bright, Ly-1dull, H-2Kkdull, ThB+, J11d+, and Lyt-2+L3T4+. Lymphocytes in the tumors were steroid-sensitive like normal thymocytes. The proportions of Lyt-2+L3T4- and Lyt-2-L3T4+ cells were generally larger in the tumors than in normal thymus and reflected the higher frequency of lymphocytes in the tumors capable of proliferating in vitro in response to Con A plus IL-2. The data were consistent with the hypothesis that the neoplasia originates from thymic epithelium that is interspersed with normal, developing thymic lymphocytes.

Neonatal thymectomy results in a repertoire enriched in T cells deleted in adult thymus

In B6AF1 mice, T lymphocytes that use the V beta 11-positive (and not V beta 6-positive or V beta 8-positive) segment in their receptor for antigen are greatly reduced in the thymus and peripheral lymphoid tissues, most likely as a result of clonal deletion. The relative number of V beta 11-positive cells in adult lymph nodes was ten times as high in B6AF1 mice thymectomized 1 to 4 days after birth as in normal mice. Moreover, for the first 10 days of life of B6AF1 mice, mature V beta 11-positive T cells were readily detected in the thymus and spleen. Thus neonatal thymectomy results in the maintenance of the receptor repertoire of early postnatal life, and this correlates with the subsequent development of organ-specific autoimmune diseases.

Transgenic HLA-DR alpha faithfully reconstitutes IE-controlled immune functions and induces cross-tolerance to E alpha in E alpha 0 mutant mice

We have constructed transgenic mice that express the human class II MHC molecule HLA-DR alpha on a genetic background in which the equivalent endogenous gene, H-2 IE alpha, is not expressed. In these mice, DR alpha complemented the E beta chain such that tissue-specific expression of an interspecies hybrid DR alpha-E beta heterodimer was obtained. Despite 25% amino acid differences between DR alpha and E alpha, immune responsiveness to IE-controlled antigens, clonal deletion of IE-reactive T cells, and alloantigenicity were quantitatively and qualitatively indistinguishable in IE-positive mice and in mice that had integrated at least four copies of the transgene. These results demonstrate a remarkable degree of structural, regulatory, and functional conservation. They also suggest that tolerance induction involves only discrete portions of MHC molecules.

Postnatal disappearance of self-reactive (V beta 6+) cells from the thymus of Mlsa mice. Implications for T cell development and autoimmunity

The postnatal ontogeny of potentially autoreactive T cells has been studied in a model system where a particular TCR beta chain variable domain (V beta 6) is correlated with reactivity to a minor antigen encoded by the Mlsa locus. Although absent among mature (CD4+ or CD8+) T cells in adult mice expressing Mlsa, brightly staining V beta 6+ cells were readily detectable in the thymus of neonatal animals, reaching a maximum after 4 d and decreasing rapidly thereafter. These V beta 6+ thymocytes were predominantly of the CD4+ phenotype and were localized in the medulla of the developing thymus. Furthermore, the intensity of TCR expression by these CD4+ cells was significantly (twofold) reduced as compared with age-matched Mlsb controls. A rapid disappearance of CD4+V beta 6+ cells (and corresponding decrease in TCR density) could also be observed in the thymus of Mlsb mice that had been injected neonatally with Mlsa spleen cells. Taken together, these results raise the possibility that some autoreactive T cells may persist after birth and that TCR downregulation may occur as a physiological response to tolerogenic signals in vivo.