The gene encoding the T-cell receptor alpha-chain maps close to the Np-2 locus on mouse chromosome 14

Development of Immature CD4+CD8+T Cells Into Mature CD4+ T Cells Requires Alpha-1 Antitrypsin as Observed by Treatment in HIV-1 Infected and Uninfected Controls

Immune cells are, by default, migratory cells that traverse tissue for the purpose of carrying out recognition and recruitment in pathologic inflammation and infection. Members of the LDL receptor family (LDL-RFMs) interact with human leukocyte elastase on the cell surface (HLE-CS) in complex with the abundant blood protein α1proteinase inhibitor (α1PI, α1-antitrypsin, Alpha-1), a process that induces internalization of aggregated functionally-related receptors, including CD4 and the T cell antigen receptor, while simultaneously promoting cellular locomotion. We sought to determine whether augmenting α1PI blood concentration would promote the locomotion of immature T cells through the thymus and generate new CD4⁺ T cells. Two small clinical trials (NCT01370018, NCT01731691, https://clinicaltrials.gov) were conducted in which HIV-1 infected and uninfected individuals were augmented with α1PI and compared with placebo-treated subjects and untreated controls. Blood cell phenotypes were monitored weekly. We found that CD4/CD8 ratio was significantly increased by α1PI augmentation in both uninfected and HIV-1 infected individuals. We found that maturation of CD4⁺CD8⁺ T cells to become immunologically competent CD4⁺ T cells was regulated by α1PI. We propose a strategy targeting HLE-CS for treating secondary immunodeficiency for which there is currently no direct treatment. Treatment to directly elevate T cells in patients with secondary immunodeficiency, including HIV disease, can be provided by alpha-1 antitrypsin augmentation or small molecules that target HLE-CS. Because individuals infected with HIV-1 produce a monoclonal antibody, 3F5, which binds to and inactivates α1PI, a process that prevents α1PI from binding to HLE-CS, thereby blocking locomotion of immature T cells through the thymus to generate CD4⁺ T cells, we further propose that HIV-1 vaccination should include induction of an antibody that binds to and blocks 3F5 activity, thereby preventing AIDS in addition to the current vaccine strategy for preventing HIV-1 infection.

Thymic Lineage Commitment Rather Than Selection Causes Genetic Variations in Size of CD4 and CD8 Compartments

During their development, immature CD4+CD8+ thymocytes become committed to either the CD4 or CD8 lineage. Subsequent complete maturation of CD4+ and CD8+ cells requires a molecular match of the expressed coreceptor and the MHC specificity of the TCR. The final size of the mature CD4+ and CD8+ thymic compartments is therefore determined by a combination of lineage commitment and TCR-mediated selection. In humans and mice, the relative size of CD4+ and CD8+ peripheral T cell compartments shows marked genetic variability. We show here that genetic variations in thymic lineage commitment, rather than TCR-mediated selection processes, are responsible for the distinct CD4/CD8 ratios observed in common inbred mouse strains. Genetic variations in the regulation of lineage commitment open new ways to analyze this process and to identify the molecules involved.

Restricted onset of T cell receptor alpha gene rearrangement in fetal and neonatal thymocytes

The initial T cell receptor (TCR) alpha gene rearrangements were analyzed in fetal and neonatal thymocyte hybridomas by Southern blotting. Interestingly, in 30% of all thymocyte hybridomas and in all fetal day 16 thymocyte hybridomas the most proximal J alpha 50 (psi J alpha) gene was rearranged. This rearrangement was found on one chromosome only and mostly in association with a delta rearrangement on the homologous chromosome. J alpha 50 was rearranged to multiple target genes based on the variable size of the restriction fragments. In addition, delta rearrangement was found with a concomitant alpha rearrangement in the majority of hybridomas and it was not only associated with J alpha 50 but with several other rearranged J alpha genes as well. Our results clearly demonstrate that T cell precursors are not pre-committed to either delta or alpha rearrangement but a flexible progenitor responds to multiple regulatory signals during T cell differentiation and they do not support the notion that delta rec-psi J alpha rearrangement is required for cell commitment to TCR alpha gene rearrangement.

Structure and diversity of the T-cell receptor alpha chain in rhesus macaque and chimpanzee

We cloned and sequenced cDNA for the TCRAC1 of a healthy rhesus monkey and chimpanzee. TCRAC1 from both nonhuman primates show extensive conservation compared to the human sequence and to other mammals. A possible primate-specific insertion near the hinge region of the TCRAC1 region is described. Characterization of 18 rhesus macaque and eight chimpanzee TCRA chain cDNA clones derived from inverse PCR revealed 12 different TCRAV and 16 different TCRAJ regions which corresponded closely to known human counterparts. One functional rhesus macaque TCRDV-TCRAJ rearrangement was detected, suggesting a genomic organization of the macaque TCRD locus which is similar to humans. At the genomic level, a single TCRAC1 gene segment was detected in rhesus macaque and chimpanzee. The close phylogenetic relationship between primates shown here for TCRA chain components supports the use of these species as animal models of human immune-mediated disease.

Gene rearrangement patterning and DNase-I hypersensitive sites within the T-cell receptor J alpha locus

For several years, the relationship between alpha beta and gamma delta T-cell progenitors has been a topic of debate. Some argue that a subset of T-cell progenitors is "pre-committed" to the alpha beta lineage and is thus programmed to rearrange alpha, but not delta genes. It is further argued that the deletion of the delta locus by a unique rearrangement, delta rec-psi J alpha, may be the critical forerunner to V-J alpha joins in alpha beta committed cells and that a hypersensitive site (HS) termed 5'TEA might regulate such rearrangement. Here we present an alternative hypothesis. We first emphasize that directed J alpha gene rearrangements do not exclusively target the psi J alpha gene, but that clustered gene rearrangements occur throughout the J alpha locus during T-cell development. We describe the existence of not one, but at least two HS sites distributed along the J alpha locus which might serve as regulators for the gene rearrangement event. Finally, we suggest that progenitor T-cells are not committed to a particular delta or alpha gene rearrangement, but that a flexible progenitor responds to complex interactions between environmental signals and multiple regulatory elements interspersed among delta/alpha genes.

The presence of an endogenous murine leukemia virus sequence correlates with the peripheral expansion of gamma delta T cells bearing the BALB invariant delta (BID) T cell receptor delta

gamma delta T cells participate in immune responses during viral, bacterial, and parasitic infections. However, it is not clear whether they recognize antigens produced by pathogens, or are actually reactive to self-ligands generated during the course of infection. In this paper, we report that the presence of the self-ligand that selectively expands a subset of gamma delta T cells correlates with the presence of an endogenous murine leukemia virus (MuLV) in inbred strains of mice. The implications of this observation for gamma delta T cell specificity and function is discussed.

Somatic cell mapping of T-cell receptor CD3 complex and CD8 genes in cattle

Bovine genes encoding T-cell receptor, CD3, and CD8 molecules have been mapped to syntenic groups using bovine x rodent hybrid somatic cells. T-cell receptor alpha and delta chains were assigned to bovine syntenic group U5, and the beta and gamma genes were syntenic with each other and with markers on U13. CD3E and CD3D genes were syntenic with each other and located to bovine syntenic group U19. CD8 was most concordant with markers of syntenic group U16, although the concordancy was only 85% and the assignment must be regarded as tentative. The comparative gene maps of human chromosome 7, bovine syntenic group U13, and mouse chromosomes 6 and 13 suggest extensive evolutionary conservation.

Transcription of germ line V alpha segments correlates with ongoing T-cell receptor alpha-chain rearrangement

M14T is a virally transformed immature T-cell line which continues to rearrange its T-cell antigen receptor (TCR) alpha-chain genes in vitro and thus represents a dynamic system for studying TCR assembly. In an effort to investigate whether the TCR alpha locus is accessible for V(D)J rearrangement events, we examined M14T cells for the presence of germ line TCR alpha transcripts. Several unrearranged V alpha segments were found to be transcriptionally active in M14T cells. By comparison, germ line V alpha transcripts are absent in nonlymphoid and pro-T-cell lines and barely detectable in mature T-cell lines, suggesting that this phenomenon is likely stage and tissue specific. We demonstrate a perfect correlation between transcriptionally active V alpha segments and their involvement in ongoing V alpha-to-J alpha rearrangements. In addition, data suggesting that the unrearranged J alpha locus is also transcriptionally active in the M14T line are presented. Furthermore, the recombination-activating genes RAG-1 and RAG-2 are differentially expressed, with RAG-2 detectable only by polymerase chain reaction, implying that very low levels of one of these gene products are sufficient to complement the other to facilitate VJ rearrangements. These findings provide the first direct evidence for an accessibility model of antigen receptor rearrangement in T cells.

Transcription of germ line V alpha segments correlates with ongoing T-cell receptor alpha-chain rearrangement

M14T is a virally transformed immature T-cell line which continues to rearrange its T-cell antigen receptor (TCR) alpha-chain genes in vitro and thus represents a dynamic system for studying TCR assembly. In an effort to investigate whether the TCR alpha locus is accessible for V(D)J rearrangement events, we examined M14T cells for the presence of germ line TCR alpha transcripts. Several unrearranged V alpha segments were found to be transcriptionally active in M14T cells. By comparison, germ line V alpha transcripts are absent in nonlymphoid and pro-T-cell lines and barely detectable in mature T-cell lines, suggesting that this phenomenon is likely stage and tissue specific. We demonstrate a perfect correlation between transcriptionally active V alpha segments and their involvement in ongoing V alpha-to-J alpha rearrangements. In addition, data suggesting that the unrearranged J alpha locus is also transcriptionally active in the M14T line are presented. Furthermore, the recombination-activating genes RAG-1 and RAG-2 are differentially expressed, with RAG-2 detectable only by polymerase chain reaction, implying that very low levels of one of these gene products are sufficient to complement the other to facilitate VJ rearrangements. These findings provide the first direct evidence for an accessibility model of antigen receptor rearrangement in T cells.

Preferential association of alpha and beta chains of the T cell antigen receptor

The cytotoxic T lymphocyte (CTL) clone B6.2.16 expresses a V beta 8.2/J beta 2.3/C beta 2-encoded T cell receptor (TcR) beta chain and an alpha chain that is encoded by a novel V alpha gene segment, J alpha 27 and C alpha. While expression of V alpha B6.2.16 and J alpha 27 is not detectable in lymph node cells of normal C57BL/6 mice, expression of these gene segments was readily seen in transgenic mice expressing the rearranged beta chain gene of the B6.2.16 T cell clone. This finding indicates that only a limited number of alpha chains can associate with the B6.2.16 beta chain and strongly suggests that the size of the TcR repertoire of mature T cells is not only limited by TcR ligand-mediated thymic selection but also by restrictions in alpha-beta combinatorial chain association.

T cell receptor beta diversity and joining segments in the NOD mouse

Pancreatic beta-cell autoantigen recognition by the immune system appears to be a critical event in the evolution of insulin dependent diabetes. Immune recognition involves antigen presentation by macrophages and subsequent antigen-peptide-class II MHC recognition by T cell receptors (TCR). Using the NOD mouse as a model for human IDD, we hypothesized that germline variability in the D beta nod and/or J beta nod segments could contribute to beta cell autoimmunity by influencing the specific peptides that are recognized. As an initial approach to our hypothesis, we sought to compare these segments to other strains of mice in search of genetic polymorphisms as reported in NZW mice. The germ line TCR beta nod gene did not display evidence of an expansion or contraction in the number of D beta nod or J beta nod segments at the level of resolution provided by restriction fragment length polymorphism analysis. The absence of such polymorphisms suggests that D beta nod or J beta nod segments are not different from nonautoimmune strains of mice.

Novel excision products of T cell receptor gamma gene rearrangements and developmental stage specificity implied by the frequency of nucleotide insertions at signal joints

We have cloned circular DNA excised by T cell receptor (TcR) gamma 1, gamma 2 and gamma 3 gene rearrangements in fetal and adult mouse thymocytes. Circular DNA contained a signal joint reciprocal to the genomic V-J coding joint. Although signal joints without nucleotide insertions are common in immunoglobulin (Ig) and TcR gene rearrangements, the signal joint of gamma found in adult thymocytes contained non-germ-line element (N) insertions at high frequency, while no insertions were found in fetal thymocytes. Thus developmental stage specificity of TcR gamma gene rearrangements is faithfully reflected on the signal joint of excision products. In addition, examination of gamma gene excision products revealed circular DNA products of TcR gamma-alpha transrearrangements, but no evidence of V gamma gene replacement in a rearranged segment.

Environmental and allele-specific influences on T cell receptor gene rearrangement: skewed alpha, delta, and gamma gene rearrangement patterns in chimeric mice

This study was performed as a means to examine the effects of environment and stem cell origin on the molding of T cell receptor gene rearrangements during T cell development. Lethally irradiated adult mice were first reconstituted with (C57BL/6 x DBA/2)F1 stem cells, which derived either from a fetal liver or adult bone marrow source. The gene rearrangements in the irradiated thymi were then compared to those in normal fetal or adult thymi by hybridoma analysis. Results showed a general absence of gene rearrangements typical of the normal fetal thymus in both sets of chimeras. alpha and gamma gene rearrangements in chimeric mice matched normal adult patterns. However, chimeric thymocytes were unique in an unusually low frequency of rearrangements at the delta locus. The use of the bone marrow vs. fetal liver as stem cell sources in chimeric mice did not affect the patterns, indicating that environmental factors played a major role in the molding of gene rearrangement at multiple T cell receptor loci. Interestingly, the chromosomal sequence added an additional influence as homologous chromosomes showed allele-specific rearrangement patterns. We now question whether the unique patterns of rearrangement in irradiated adult thymi may substantially affect developing T cell populations in chimeric animals, particularly with regard to the gamma/delta T cell subset. Further analyses are warranted, both in experimental and clinical settings, regarding ultimate potentials for T cell diversity and function in transplantation recipients.

Genetic control of Coxsackievirus B3-induced heart-specific autoantibodies associated with chronic myocarditis

Cardiac-specific autoantibodies to sarcolemmal and cardiac myosin antigens observed during the chronic phase of Coxsackievirus B3-induced myocarditis appear to be under autosomal recessive control. This observation is based on examination of F1 hybrids bred from A/J mice which develop chronic myocarditis and C57BL/6J mice which resolve the virus-induced lesions. Previous mouse studies demonstrated that the prevalence of heart-specific autoantibodies varied with the H-2 complex. However, in 25 H-2 congenic mouse strains the strain background was the predominant determinant of autoantibody presence. Recently, we extended our genetic evaluation of the chromosomal locations governing autoantibody responses by examining 25 AXB and BXA recombinant inbred strains. Two populations of heart-specific autoantibodies were demonstrated against sarcolemmal and cardiac myosin antigens. Analyses of the AXB/BXA strain distribution patterns for these two traits revealed that the anti-sarcolemmal response was controlled by a gene(s) linked to Np-2 and Ter alpha loci on chromosome 14. Linkage could not be assigned for the anti-cardiac myosin response.

Surface expression of a T cell receptor beta (TCR-beta) chain in the absence of TCR-alpha, -delta, and -gamma proteins

The antigen receptor expressed by mature T cells has been described as a disulfide-linked alpha/beta or gamma/delta heterodimer noncovalently associated with CD3, a complex of transmembrane proteins that communicates signals from the T cell receptor (TCR) to the cell interior. Studies suggest that all component chains must assemble intracellularly before surface expression can be achieved. We described, however, a CD4+/CD8+ transformed murine thymocyte, KKF, that expresses surface TCR-beta chains in the absence of gamma, delta, and alpha proteins; these beta chains are only weakly associated with CD3-epsilon and CD3-zeta. Furthermore, KKF responds differently to stimulation through TCR-beta and CD3-epsilon, a functional dissociation that has been ascribed to a CD4+/CD8+ subpopulation of normal thymocytes. KKF's unique TCR structure may offer an explanation for the functional anomalies observed.

Developmental T cell receptor gene rearrangements: relatedness of the alpha/beta and gamma/delta T cell precursor

To examine the relationships between T cell populations at various stages of development, T cell receptor (TcR) gene rearrangements were compared between the four murine populations of (a) early thymocytes, (b) early splenocytes, (c) adult thymocytes and (d) adult splenocytes. TcR alpha gene rearrangements were shown to progress from 5' to 3' regions of the J alpha locus and from 3' to 5' regions of the V alpha locus during the development of T cells in both the thymus and spleen. Thus, the gene rearrangement potentials of proximal genes varied with age, yielding a biased repertoire in the young vs. adult animal. As evidence that gamma/delta and alpha/beta gene rearrangements appeared concomitantly in individual precursors, it was found that: (a) multiple adult thymocytes bore alpha gene rearrangements on one chromosome and delta gene rearrangements on the homologous chromosome, and (b) V gamma 3-J gamma 1 rearrangements, prominent joins in the early gamma/delta T cell population, were also prominent in the early alpha/beta T cell subset. These data illustrate the non-random nature of the developmental TcR gene rearrangement and suggest that alpha/beta and gamma/delta T cell populations derive from related, if not identical, T cell precursor populations.

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.

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.

An interspecific backcross linkage map of the proximal half of mouse chromosome 14

We have generated a 30-cM molecular genetic linkage map of the proximal half of mouse chromosome 14 by interspecific backcross analysis. Loci that were mapped in this study include Bmp-1, Ctla-1, Hap, hr, Plau, Psp-2, Rib-1, and Tcra. A region of homology between mouse chromosome 14 and human chromosome 10 was identified by the localization of Plau to chromosome 14. This interspecific backcross map will be valuable for establishing linkage relationships of additional loci to mouse chromosome 14.

A complex of serine protease genes expressed preferentially in cytotoxic T-lymphocytes is closely linked to the T-cell receptor alpha- and delta-chain genes on mouse chromosome 14

A complex of genes encoding serine proteases that are preferentially expressed in cytotoxic T-cells was shown to be closely linked to the T-cell receptor alpha- and delta-chain genes on mouse chromosome 14. A striking difference in recombination frequencies among linkage crosses was reported. Two genes, Np-1 and Tcra, which fail to recombine in crosses involving conventional strains of mice, were shown to recombine readily in interspecific crosses involving Mus spretus. This difference in recombination frequency suggests chromosomal rearrangements that suppress recombination in conventional crosses, recombination hot spots in interspecific crosses, or selection against recombinant haplotypes during development of recombinant inbred strains. Finally, a mutation called disorganization, which is located near the serine protease complex, is of considerable interest because it causes an extraordinarily wide variety of congenital defects. Because of the involvement of serine protease loci in several homeotic mutations in Drosophila, disorganization must be considered a candidate for a mutation in a serine protease-encoding gene.

Structure and expression of the T cell receptor gamma locus in pre-B and early hemopoietic cells

The genetic structure and expression of the T cell receptor (TcR) loci were examined in pre-B and early hemopoietic cells. Thirty-eight percent of Abelson murine leukemia virus-transformed pre-B cell lines were rearranged at TcR gamma. Moreover, many pre-B cell lines were rearranged at two distinct gamma loci, V gamma 1.2 and V gamma 2. The gamma rearrangements in the pre-B cell lines were similar to those observed previously in T cell lines. V + C-containing gamma mRNA was detected in two pre-B cell lines. In all other pre-B and interleukin (IL) 3-dependent lymphoid and myeloid lines examined, smaller C gamma-containing mRNA were detected. These C gamma transcripts were independent of the genetic configuration of the gamma locus. In contrast, the TcR alpha and beta loci were in the germ-line configuration in all non-T cell lines examined and mRNA encoding these loci were not detected. When IL3-dependent lymphoid and myeloid cell lines were transformed to growth factor independence by a non-autocrine mechanism, no mRNA transcripts encoding TcR C gamma were detected. However, TcR C gamma mRNA transcripts were detected in factor-independent cell lines that arose by an autocrine mechanism. The cell cycle expression of C gamma was compared with protooncogenes and other marker genes previously shown to be cell cycle specific. mRNA transcripts encoding C gamma were detected in the highest amounts 4-8 h after IL 3, but not phorbol myristate acetate, addition. A similar time period of expression was observed with ornithine decarboxylase which has been shown to be expressed in G1 phase. These observations indicate that TcR gamma is often rearranged in pre-B cell lines and may be directly regulated by IL3 in IL3-dependent cells.

Qa-1 restricted recognition of foreign antigen by a gamma delta T-cell hybridoma

Distinct T-lymphocyte subsets recognize antigens in conjunction with different classes of major histocompatibility complex (MHC) glycoproteins using the T-cell receptor (TCR), a disulphide-linked heterodimer associated with the CD3 complex on the cell surface. In general, class I and class II MHC products provide a context for the recognition of foreign antigens by CD8+ and CD4+ T cells, respectively. This recognition seems to be largely dependent on alpha beta TCR heterodimers, whereas the function of the second gamma delta TCR, present on a minor subpopulation of cells, is still unknown. In the mouse, the existence of six cell-surface MHC class I products (K, D, L, Qa-1, Qa-2 and Tla) has been firmly established by serological, biochemical and genetic evidence. So far, only the most polymorphic of them, K, D and L ('classical' class I) have been reported as restriction elements for T-cell recognition of foreign antigens. The function of the relatively invariant Qa and Tla molecules remains unknown. We have made a T-helper cell hybridoma clone (DGT3) that recognizes synthetic copolymer poly(Glu50Tyr50) in the context of Qa-1 cell surface product, and has a CD4-CD8- phenotype. Our studies indicate that DGT3 cells express the gamma delta TCR on the cell surface, implicating its role in Qa-1-restricted antigen recognition. This is the first evidence that T cells can recognize foreign antigen in association with self Qa product, confirming that Qa molecules not only topologically, but also functionally, belong to the MHC.

Complexity, polymorphism, and recombination of mouse T-cell receptor alpha gene families

Genomic DNA from a large panel of inbred strains of mice were hybridized sequentially with 15 V alpha, 2 V delta, 1 C alpha, and 1 C delta probes. Most of the V alpha probes detected a high degree of polymorphism and have allowed the definition of five mouse T-cell receptor alpha (Tcr alpha) haplotypes. One of these haplotypes (Tcre alpha) appears to arise from a recombination between the Tcrb alpha and Tcra alpha haplotypes, the latter being the most frequently found in the conventional inbred strains. This recombination event clearly indicates that the members of at least 11 V alpha sub-families are not closely linked but highly interspersed with one another on chromosome 14.

The murine retinoblastoma homolog maps to chromosome 14 near Es-10

Restriction fragment length variants have been exploited to map genetically Rb-1, the murine homolog of the human retinoblastoma gene. Rb-1 localized to mouse chromosome 14 on the basis of results from analysis of somatic cell hybrids. In an interspecific backcross involving Mus spretus, Rb-1 and the murine homolog of the human esterase D gene (ESD), which we refer to here as Esd, were inseparable. Furthermore, the strain distribution patterns of Rb-1 and Es-10 are the same in 31 of 32 recombinant inbred strains. Close linkage of the chromosome 14 morphological marker hairless (hr) to Rb-1 is also implied. These results localize Rb-1 on the mouse linkage map and provide close genetic markers to follow Rb-1 in somatic as well as in germline genetic experiments. Additionally, the results suggest that Es-10 is the murine homolog of ESD and provide further evidence for linkage conservation during mammalian evolution.

Restriction fragment length polymorphisms of the mouse T-cell receptor gene families

We have studied the restriction fragment length polymorphisms (RFLPs) found in the germline T-cell receptor genes of 25 inbred Mus musculus strains and 8 wild Mus species. Included in the inbred mice tested were several strains which spontaneously develop systemic autoimmune disease. Extensive polymorphism was evident for the variable (V) gene segments of the alpha gene family for both the inbred strains and wild mouse species. Changes in the total number of bands hybridizing with probes for V alpha gene segments suggest that members of a V alpha gene segment subfamily are not closely linked, but are interspersed with members of other subfamilies; that expansion and contraction of the multimembered subfamilies may be an important diversifying factor. Our data obtained with beta gene probes revealed genomic diversity that is much more limited than that seen for the alpha locus. Analysis of inbred mice with probes for the gamma gene locus revealed some RFLPs, but little evidence of expansion or contraction in the numbers of gene segments. Among the autoimmune mice, NZW, NZB, and BXSB/MpJ all display distinctive differences with alpha gene probes. NZW mice have a large deletion of the beta gene family, which has been reported previously. We found no differences to distinguish the MRL/MpJ lpr/lpr mice from non-autoimmune strains.

The role of T cell receptors in non-MHC-restricted cytotoxicity

The relationship between natural killer cells (NK) and cells of the T lineage has been obscured by the existence of poorly characterized clones of presumed NK origin. We have analyzed nine of these cloned cell lines displaying varying levels of cytotoxic activity against NKS YAC-1 target cells for rearrangement and expression of the genes encoding the alpha, beta, and gamma chains of the T cell receptor for antigen. Rearrangements at both the TcR beta and gamma loci were detected in all clones often at both alleles. Rearrangement patterns at the TcR beta locus were identical in several clones, despite different degrees of cytotoxicity. T cell receptor alpha, beta, and gamma genes were expressed as full length transcripts in all clones regardless of their levels of cytotoxic activity. To explore the involvement of cell surface molecules in the cytolytic events, studies were undertaken to determine whether cytotoxic activity could be inhibited by antibodies against CD3, LFA-I, and H-2KdDd. In two selected clones, both alpha and beta chains of the LFA-I molecule were expressed but only monoclonal antibodies against the alpha chain significantly blocked cytotoxicity. Cytotoxicity was also inhibited by monoclonal antibodies against epitopes of H-2KdDd and CD3, the extent of inhibition correlating with the level of surface expression on both clones. These data suggest that conventional alpha/beta heterodimers may be necessary but not sufficient for target cell recognition by these clones. Since T cell receptor rearrangement and expression occur normally in the T cell lineage but not the NK lineage, these results also indicate that a subpopulation of cells with non-MHC-restricted killer activity lies on the T cell differentiation pathway and is selected by in vitro growth with IL-2. The limited rearrangement pattern observed can be explained if only a small subpopulation of T cells is capable of non-MHC-restricted killing, and if certain rearrangements favor self-MHC recognition which is known to block cytolysis in the NK system.

Proximity of the CTLA-1 serine esterase and Tcr alpha loci in mouse and man

The serine esterase CTLA-1 gene was shown by in situ hybridization to map to the D segment of mouse chromosome 14, the same localization as a member of the immunoglobulin superfamily, Tcr alpha. To further demonstrate the proximity of CTLA-1 and Tcr alpha, genetic linkage was tested in mouse using restriction fragment length polymorphisms and a backcross progeny, and no recombination was observed in the 100 backcross products studied. Recombination events between Tcr alpha/CTLA-1 and the markers Gdh-X and NP-1 show that the most probable order of these loci in the mouse 14D region is NP-1-Tcr alpha/Ctla-1-Gdh-X. In man, the human homologue of CTLA-1 was shown by in situ hybridization to map on chromosome 14, at 14q11-q12, where Tcr alpha also maps. Using the human cell line SUP-T1, bearing the inversion inv(14) (q11;q32), we further demonstrated the loci order in man to be centromere-NP-1-Tcr alpha-CTLA-1. To complement the cytogenetic and genetic mapping data, we tried to determine the physical distance between the two genes by pulsed field gel electrophoresis (PFGE). DNA prepared from various cell types, both mouse and human, were digested with a panel of rare cutter enzymes and hybridized first with CTLA-1, then with Tcr alpha probes. None of the bands identified hybridized with both Tcr alpha and CTLA-1 probes for either mouse or human cells. Although the physical mapping by PFGE is inconclusive, the cytogenetic and genetic data support close linkage of the Tcr alpha and CTLA-1 genes in both mouse and man, suggesting homology between the D region of mouse chromosome 14 and the q11-q12 region of human chromosome 14, encompassing the Tcr alpha and CTLA-1 loci. These findings also provide another example of proximity of genes coding for a member of the Ig super-family and a serine esterase.

Unresponsiveness to a foreign antigen can be caused by self-tolerance

In mice, two sets of genes govern the immune response to the synthetic antigen GT. One maps to the major histocompatibility complex and behaves like a typical immune response gene. The second is a background gene encoding a cell surface structure found on B cells. Mice which express, and are therefore tolerant of, one form of this structure do not respond to GT. Thus, tolerance of self generates holes in the T-cell repertoire, partially crippling the immune system.

The joining of germ-line V alpha to J alpha genes replaces the preexisting V alpha-J alpha complexes in a T cell receptor alpha, beta positive T cell line

To determine whether T cell receptor genes follow the same principle of allelic exclusion as B lymphocytes, we have analyzed the rearrangements and expression of TCR alpha and beta genes in the progeny of the CD3+, CD4-/CD8- M14T line. Here, we show that this line can undergo secondary rearrangements that replace the pre-existing V alpha-J alpha rearrangements by joining an upstream V alpha gene to a downstream J alpha segment. Both the productively and nonproductively rearranged alleles in the M14T line can undergo secondary rearrangements while its TCR beta genes are stable. These secondary recombinations are usually productive, and new forms of TCR alpha polypeptides are expressed in these cells in association with the original C beta chain. Developmental control of this V alpha-J alpha replacement phenomenon could play a pivotal role in the thymic selection of the T cell repertoire.

In transgenic mice the introduced functional T cell receptor beta gene prevents expression of endogenous beta genes

Transgenic mice were constructed with a functional T cell receptor beta gene. Transcription of the introduced gene is largely confined to T cells, but low levels of transcripts are also seen in B cells and in other tissues. Serological analyses show that most, if not all, of the T lymphocytes express the transgenic beta chain on the cell surface and lack beta chains encoded by endogenous beta genes. Molecular genetic analyses of uncloned and cloned T lymphocytes demonstrate that rearrangement of endogenous beta genes is incomplete. Partial D beta 1-J beta 1 rearrangements are found preferentially, while complete VDJ rearrangements are not seen. These findings show that expression of the transgene regulates the rearrangement of endogenous beta genes. Although the alpha beta T cell receptors of the transgenic mice are homogeneous with respect to the beta chain, they are fully functional, at least in a variety of allogeneic responses.

Progression of rearrangements at T cell receptor beta and gamma gene loci during athymic differentiation of bone marrow cells in vitro

A previously described in vitro system that supports T cell differentiation from bone marrow (BM) precursors was analyzed for T cell receptor gene rearrangement and expression. Cultured populations from days (d.) 0, 3, 6, and 12-13 were fused with BW5147. Only hybridomas from d.6 and d.12-13 bore BM-derived rearrangements. The rearrangement complexity was higher on d.12 than d.6 in that patterns consistent with D beta 1-J beta 1 and D beta 2-germ-line configurations decreased while V-D-J beta 2 and V gamma 2-J gamma 1 joining became dominant. Northern blots of d.13 BM cultures revealed gamma, alpha, and beta (1.0 and 1.3 kb) transcripts. Parallels between patterns in BM cultures and thymus ontogeny were recognized.

Selection of amino acid sequences in the beta chain of the T cell antigen receptor

The induction of an immune response in mammals is initiated by specifically reactive T lymphocytes. The specificity of the reaction is mediated by a complex receptor, part of which is highly variable in sequence and analogous to immunoglobulin heavy- and light-chain variable domains. The functional specificity of the T cell antigen receptor is, however, markedly different from immunoglobulins in that it mediates cell-cell interactions via the simultaneous recognition of foreign antigens and major histocompatibility complex-encoded molecules expressed on the surface of various lymphoid and nonlymphoid cells. The relation between the structure of the receptor and its functional specificity was investigated by analyzing the primary sequences of the receptors expressed by a series of T lymphocyte clones specific for a model antigen, pigeon cytochrome c. Within this set of T lymphocyte clones there was a striking selection for amino acid sequences in the receptor beta-chain in the region analogous to the third complementarity-determining region of immunoglobulins. Thus, despite the functional differences between T cell antigen receptors and immunoglobulin molecules, analogous regions appear to be important in determining ligand specificity.

Thymocyte clones from 14-day mouse embryos. I. State of T cell receptor genes, surface markers, and growth requirements

We have established in culture 13 clones from the thymus of a 14-d B10.BR mouse embryo and characterized 8 of them. All eight FT clones have the TCR-gamma and -beta genes in germline configuration. They express mRNA for the gamma, but not for the beta nor the alpha genes. All eight FT clones are Thy-1+, Ly-1+, LFA-1+, Pgp-1+, H-2K+, and T3-. Three phenotypes could be distinguished on the basis of Lyt-2, L3T4, and IL-2-R expression: Lyt-2+, L3T4-, IL-2-R+ (I); Lyt-2+, L3T4-, IL-2-R- (II); and Lyt-2+, L3T4+, IL-2-R+ (III) cells. All eight clones grow in rIL-4 and six clones also proliferate in rIL-2. Antibodies specific for IL-2-R inhibit their response to rIL-2 but not to rIL-4. The eight FT clones synthesize mRNA for IL-4 after stimulation in vitro and none of them exhibit cytolytic activity or helper function for B lymphocytes. We conclude that the FT clones are at a very early stage of T cell development, that the expression of Lyt-2 and L3T4 surface molecules can precede that of the antigen receptor, and that the same fetal thymocyte can use both IL-4 and IL-2 as growth factor.

Transient rearrangements of the T cell antigen receptor alpha locus in early thymocytes

The dull Ly-1 double-negative (Ly-1dull, Lyt-2-, L3T4-) subpopulation appears to be the major precursor group of T lymphocytes in the thymus. In examining the status of the alpha, beta, and gamma chain genes for T cell receptors (TCR) in this population of cells and hybridomas made from them, we find that all of these loci appear to begin DNA rearrangements in a nearly simultaneous fashion. In the case of the gamma genes, these involve V gamma----J gamma C gamma gene rearrangements; with the beta chain genes, both D beta----J beta C beta rearrangement and V beta----D beta J beta C beta rearrangements are evident; and in the case of the alpha locus, assayed in part by pulsed-field gel electrophoresis, they take the form of a novel series of rearrangements occurring 80 kb or more 5' to the C alpha gene. These alpha locus rearrangements are well away from any of the J alpha gene segments found in cDNA clones to date and are deleted in most mature thymocytes and functional T cell lines. Therefore they appear to represent a distinct class of rearrangement that occurs before V alpha----J alpha joining. These distinctions between the character of the TCR gene rearrangements in these cells represent useful markers in further distinguishing different stages of T cell differentiation within this compartment of early T cells. In addition, the unexpected discovery of clonal rearrangements so far away from any of the expressed J alpha gene segments, and at a stage where there is little or no stable C alpha RNA present, has interesting implications for the hierarchy of TCR gene expression.

Transcription of a T cell receptor beta chain gene in L cell fibroblasts following DNA-mediated gene transfer

Functionally rearranged T cell receptor alpha and beta-chain genes from a fluorescein-specific cytotoxic T cell clone have been introduced, together with the selectable marker gene neo, into mouse fibroblasts (L cells) by electroporation. Transformed cells were selected for neo gene expression by growth in medium containing the antibiotic G418. Southern blot analysis of DNA from transformed L cell clones revealed that the endogeneous T cell receptor alpha and beta-chain genes were in germ-line configuration and that in 4 of the 6 clones examined the exogenously introduced rearranged alpha and beta chain genes were present. The introduced beta-chain gene is transcriptionally active in two L cell clones examined whereas no transcription of the alpha-chain gene could be detected in the same transformants.

Genomic organization of the mouse T-cell receptor beta-chain gene family

We have combined three different methods, deletion mapping of T-cell lines, field-inversion gel electrophoresis, and the restriction mapping of a cosmid clone, to construct a physical map of the murine T-cell receptor beta-chain gene family. We have mapped 19 variable (V beta) gene segments and the two clusters of diversity (D beta) and joining (J beta) gene segments and constant (C beta) genes. These members of the beta-chain gene family span approximately equal to 450 kilobases of DNA, excluding one potential gap in the DNA fragment alignments.

Mouse DNA 'fingerprints': analysis of chromosome localization and germ-line stability of hypervariable loci in recombinant inbred strains

Human minisatellite probes cross-hybridize to mouse DNA and detect multiple variable loci. The resulting DNA "fingerprints" vary substantially between inbred strains but relatively little within an inbred strain. By studying the segregation of variable DNA fragments in BXD recombinant inbred strains of mice, at least 13 hypervariable loci were defined, 8 of which could be regionally assigned to mouse chromosomes. The assigned loci are autosomal, dispersed and not preferentially associated with centromeres or telomeres. One of these minisatellites is complex, with alleles 90 kb or more long and with internal restriction endonuclease cleavage sites which produce a minisatellite "haplotype" of multiple cosegregating fragments. In addition, one locus shows extreme germ-line instability and should provide a useful system for studying more directly the rates and processes of allelic variation of minisatellites.