Inhibition of abnormal T cell development and autoimmunity in gld mice by transgenic T cell receptor beta chain

Fas-dependent elimination of nonselected CD8 cells and lpr disease

MHC/self peptide interactions with cognate coreceptor/TCR complexes are central to homeostasis of the T cell repertoire. Recent reports have also underlined the critical role of IL-15/IL-2 cytokines in regulating this homeostatic process. In this study, we investigate mechanisms that regulate potentially autoreactive CD8 cells that have escaped intrathymic selection. These cells, upon exit from the thymus, express high levels of CD44, B220, and the IL-15R/IL-2R, and undergo fas-dependent apoptosis. Defects in fas signaling allow increased IL-15/IL-2-dependent survival of these CD44/B220(+) CD8(+) as well as the double-negative T cells characteristic of lpr disease.

Inhibition of NF-kappaB in T cells blocks lymphoproliferation and partially rescues autoimmune disease in gld/gld mice

The Fas ligand (FasL)/Fas pathway is crucial for the maintenance of homeostasis of the peripheral immune system. Its importance is illustrated by the spontaneous mouse mutants gld andlpr which lack functional FasL and Fas receptor, respectively. These animals develop lymphadenopathy, splenomegaly, increased serum Ig and autoantibodies, leading to an autoimmune syndromeand premature death. The Rel/NF-kappaB family of transcription factors plays an important role in peripheral lymphocyte proliferation and survival. In this report, we studied the consequences of T cell-specific inhibition of NF-kappaB on the development of the gld phenotype. Transgenic gld/gld mice expressing a non-degradable form of IkappaBalpha under the control of T cell-specific regulatory elements show dramatically reduced lymphadenopathy, splenomegaly, and an almost complete elimination of Thy-1(+)B220(+)CD4(-)CD8(-) abnormal T cells, correlating with reduced proliferative responses and increased apoptosis of peripheral T cells upon TCR triggering. Interestingly, the B cell abnormalities that are characteristic of gld/gld mice, such as the production of autoantibodies, high levels of serum Ig, and the development of glomerulonephritis, are partially corrected. These results suggest that the T cell-specific inhibition of NF-kappaB opens apoptotic pathways distinct from FasL/Fas which, along with a diminished proliferative response, blocks splenomegaly and lymphadenopathy and partially rescues autoimmune disease in gld/gld mice.

Differential roles of Fas ligand in spontaneous and actively induced autoimmune encephalomyelitis

To determine the roles of Fas/Fas ligand (FasL) in autoimmunity, we studied spontaneous and actively induced autoimmune encephalomyelitis in 541 myelin basic protein-specific T cell receptor transgenic mice. We found that spontaneous autoimmune encephalomyelitis, which was initiated by unidentified microbial factors, was dramatically exacerbated in mice carrying Fas or FasL gene mutation. The exacerbation of autoimmune encephalomyelitis was reflected primarily by an increase in disease incidence and a decrease in spontaneous disease recovery. By contrast, actively induced encephalomyelitis, which was initiated by pertussis toxin, was significantly inhibited by Fas or FasL gene mutation. These results suggest that environmental factors that trigger autoimmune disease may determine not only whether disease will occur but also whether an immune molecule such as FasL will promote or inhibit the autoimmune process.

A Tailless Fas-FADD Death-Effector Domain Chimera Is Sufficient to Execute Fas Function in T Cells But Not B Cells of MRL-lpr/lpr Mice

The Fas receptor delivers signals crucial for lymphocyte apoptosis through its cytoplasmic death domain. Several Fas cytoplasmic-associated proteins have been reported and studied in cell lines. So far, only Fas-associated death domain protein (FADD), another death domain-containing molecule has been shown to be essential for Fas signals in vivo. FADD is thought to function by recruiting caspase-8 through its death-effector domain. To test whether FADD is sufficient to deliver Fas signals, we generated transgenic mice expressing a chimera comprised of the Fas extracellular domain and FADD death-effector domain. Expression of this protein in lymphocytes of Fas-deficient MRL-lpr/lpr mice completely diminishes their T cell but not their B cell abnormalities. These results suggest that FADD alone is sufficient for initiation of Fas signaling in primary T cells, but other pathways may operate in B cells.

Thymic Expression of the Transcription Factor Nur77 Rescues the T Cell But Not the B Cell Abnormality of gld/gld Mice

Fas and Fas ligand are critical regulators of lymphocyte homeostasis. Disruption of this pathway in the spontaneous mouse mutant gld leads to autoimmunity characterized by the appearance of a population of CD4−8−B220+ T cells and the production of autoantibodies. Nur77 is a transcription factor that is induced upon TCR signaling. Constitutive thymic expression of Nur77 leads to apoptosis. We have previously shown that introduction of this Nur77 transgene can eliminate the accumulation of abnormal T cells in the periphery of gld/gld mice. In this report, we further characterized the effects of the Nur77 transgene on the gld phenotype. Nur77-mediated apoptosis is evident in the thymuses of mice with either a gld/gld homozygous or gld/+ heterozygous background. Consequently, few mature T cells are generated in these mice. In addition, mature T cells exhibit a diminished response to proliferative signals through CD3. Interestingly, the Nur77 transgene failed to reduce serum levels of Igs and anti-DNA Abs to wild-type levels. These data suggest that the rescue of the T cell lymphoproliferative syndrome in gld/gld mice by the Nur77 transgene is mediated by events in the thymus and that B cell autoimmune disease associated with the gld mutation can develop independently of the T cell abnormality.

Separately expressed T cell receptor alpha and beta chain transgenes exert opposite effects on T cell differentiation and neoplastic transformation

Two aspects of T cell differentiation in T cell receptor (TCR)-transgenic mice, the generation of an unusual population of CD4-CD8-TCR+ thymocytes and the absence of gamma delta cells, have been the focus of extensive investigation. To examine the basis for these phenomena, we investigated the effects of separate expression of a transgenic TCR alpha chain and a transgenic TCR beta chain on thymocyte differentiation. Our data indicate that expression of a transgenic TCR alpha chain causes thymocytes to differentiate into a CD4-CD8-TCR+ lineage at an early developmental stage, depleting the number of thymocytes that differentiate into the alpha beta lineage. Surprisingly, expression of the TCR alpha chain transgene is also associated with the development of T cell lymphosarcoma. In contrast, expression of the transgenic TCR beta chain causes immature T cells to accelerate differentiation into the alpha beta lineage and thus inhibits the generation of gamma delta cells. Our observations provide a model for understanding T cell differentiation in TCR-transgenic mice.

Light chain editing in kappa-deficient animals: a potential mechanism of B cell tolerance

The genetic organization of the kappa and lambda light chain loci permits multiple, successive rearrangement attempts at each allele. Multiple rearrangements allow autoreactive B cells to escape clonal deletion by editing their surface receptors. Editing may also facilitate efficient B cell production by salvaging cells with nonproductive light chain (L chain) rearrangements. To study receptor editing of kappa L chains, we have characterized B cells from mice hemizygous for the targeted inactivation of kappa (JCkD/wt) which have an anti-DNA heavy chain transgene, 3H9. Hybridomas from JCkD/wt mice exhibited an increased frequency of rearrangements to downstream Jk segments (such as Jk5) compared with most surveys from normal mice, consistent with receptor editing by sequential kappa locus rearrangements in JCkD/wt. We observed an even higher frequency of rearrangements to Jk5 in 3H9 JCkD/wt animals compared with nontransgenic JCkD/wt, consistent with editing of autoreactive kappa in 3H9 JCkD/wt. We also recovered a large number of 3H9 JCkD/wt lines with Vk12/13-Jk5 rearrangements and could demonstrate by PCR and Southern analysis that up to three quarters of these lines underwent multiple kappa rearrangements. To investigate editing at the lambda locus, we used homozygous kappa-deficient animals (JCkD/JCkD and 3H9 JCkD/JCkD). The frequencies of V lambda 1 and V lambda 2 rearrangements among splenic hybridomas in 3H9 JCkD/JCkD were reduced by 75% whereas V lambda X was increased 5-10-fold, compared with nontransgenic JCkD/JCkD animals. This indicates that V lambda 1 and V lambda 2 are negatively regulated in 3H9 JCkD/JCkD, consistent with earlier studies that showed that the 3H9 heavy chain, in combination with lambda 1 binds DNA. As successive lambda rearrangements to V lambda X do not inactivate V lambda 1, the consequence of lambda editing in 3H9 JCkD/JCkD would be failed allelic exclusion at lambda. However, analysis of 18 3H9 JCkD/JCkD hybridomas with V lambda 1 and V lambda X DNA rearrangements revealed that most of these lines do not have productive lambda 1 rearrangements. In sum, both kappa and lambda loci undergo editing to recover from nonproductive rearrangement, but only kappa locus editing appears to play a substantial role in rescuing autoreactive B cells from deletion.

T cell receptor (beta chain) transgenic mice have selective deficits in gamma delta T cell subpopulations

TCR-beta (T cell receptor-beta chain) transgenic mice have altered lymphocyte development. TCR-beta transgenic mice are hyporesponsive to alloantigens in vivo and are deficient in gamma delta T cells. In order to begin a study of the relationship between a deficiency of alloreactive gamma delta cells and the defective function of in vivo alloantigen recognition, we analysed the gamma delta T cell development in TCR-beta mice. The presence of the TCR-V beta 8.2 chain transgene is associated with inhibition of gamma chain gene rearrangement. In order to determine how the presence of the TCR-beta transgene affects gamma delta T cell development, gamma delta T cells were studied in the skin, intestine and spleen. TCR-beta mice have dramatically reduced numbers of gamma delta T cells in the spleen and moderately reduced numbers of gamma delta T cells among intestinal intraepithelial lymphocytes. In contrast, these mice have normal numbers of gamma delta dendritic epidermal cells (DEC). These selective deficits could be due to the developmental regulation of transgene transcription during fetal life. We examined transcription of the TCR-beta transgene in the fetal thymus and found that the TCR-beta transgene is first transcribed at high levels on day 16 of fetal life, after DEC have already migrated from the thymus to the epidermis. Furthermore, mRNA from the transgene was detected in DEC, ruling out the formal possibility that DEC bear a gamma delta receptor only because they are incapable of expressing the transgene.(ABSTRACT TRUNCATED AT 250 WORDS)

Gld and lpr mice: single gene mutant models for failed self tolerance

Mice homozygous for the gld or lpr mutations develop autoimmunity, and a lymphoproliferative disorder involving accumulation of huge numbers of unusual CD4-CD8-TCR alpha beta lo T cells. Here we review our past work with gld mice, and attempt to explain lymphoproliferation in terms of current models of T cell maturation and self-tolerance induction. The availability of molecular probes to the gene products of lpr and gld should shortly lead to a better understanding of the acquisition of self tolerance during T cell maturation and of autoimmunity.

B lymphocytes may escape tolerance by revising their antigen receptors

To explore mechanisms that prevent autoreactivity in nonautoimmune mice, endogenous immunoglobulin (Ig) light (L) chains that associate with a transgenic anti-DNA heavy chain were analyzed. The antibodies from splenic B cell hybridomas of such mice did not bind double-stranded DNA (dsDNA) and their L chain sequences showed a biased use of V kappa and J kappa gene segments. The 44 L chains in this survey were coded for by just 18 germline genes. Six of the genes, each belonging to a different V kappa group, were used more than once and accounted for three fourths of all sequences. Based on the distribution of V kappa genes, the L chain repertoire in this line of transgenic mice was estimated at 37 V kappa genes. The most frequently observed gene, a member of the V kappa 12/13 group, was identified in 16 hybrids. In addition, the majority of V kappa genes used J kappa 5. We interpret the skewed representation of V kappa and J kappa gene segments to result from negative selection. Based on the data, we suggest that V kappa rearrangements giving rise to anti-dsDNA reactivity are removed from the repertoire by a corrective mechanism capable of editing self-reactive Ig.