Shp1 regulates T cell homeostasis by antagonizing IL-4 signalling (P1312)

The tyrosine phosphatase Shp1 is expressed ubiquitously in hematopoietic cells and is generally viewed as a negative regulator. Null mutations in Ptpn6, which encodes Shp1, result in the motheaten phenotype, characterized by widespread inflammation that causes death by 3-4 weeks of age. Previous studies of motheaten mice identified Shp1 as a negative regulator of TCR signaling, but the severe inflammation in these mice could have confounded our understanding of Shp1 function in T cell biology. To define the T cell intrinsic role of Shp1, we have characterized T cell-specific conditional knockout mice. Surprisingly, we detect no changes in TCR responsiveness in Shp1-deficient thymocytes or peripheral T cells. Instead, T cell Shp1 KO mice are enriched for memory-phenotype T-cells that express elevated levels of CD44 in the periphery. In addition, activated Shp1-deficient CD4+ T cells skew to Th2 and produce elevated levels of IL-4. Following IL-4 stimulation, Stat 6 activation is sustained in Shp1 deficient T-cells, leading to enhanced IL-4 production. Elimination of IL-4, through in vivo administration of a neutralizing antibody or by crossing to IL-4 KO mice, results in marked reduction of the excessive memory-like population in T cell specific Shp1 KO mice. Therefore, Shp1 is an essential negative regulator of IL-4 signaling in and is critical for the maintainance of T cell homeostasis.

Dysregulation of cell polarity proteins synergize with oncogenes or the microenvironment to induce invasive behavior in epithelial cells

Changes in expression and localization of proteins that regulate cell and tissue polarity are frequently observed in carcinoma. However, the mechanisms by which changes in cell polarity proteins regulate carcinoma progression are not well understood. Here, we report that loss of polarity protein expression in epithelial cells primes them for cooperation with oncogenes or changes in tissue microenvironment to promote invasive behavior. Activation of ErbB2 in cells lacking the polarity regulators Scribble, Dlg1 or AF-6, induced invasive properties. This cooperation required the ability of ErbB2 to regulate the Par6/aPKC polarity complex. Inhibition of the ErbB2-Par6 pathway was sufficient to block ErbB2-induced invasion suggesting that two polarity hits may be needed for ErbB2 to promote invasion. Interestingly, in the absence of ErbB2 activation, either a combined loss of two polarity proteins, or exposure of cells lacking one polarity protein to cytokines IL-6 or TNFα induced invasive behavior in epithelial cells. We observed the invasive behavior only when cells were plated on a stiff matrix (Matrigel/Collagen-1) and not when plated on a soft matrix (Matrigel alone). Cells lacking two polarity proteins upregulated expression of EGFR and activated Akt. Inhibition of Akt activity blocked the invasive behavior identifying a mechanism by which loss of polarity promotes invasion of epithelial cells. Thus, we demonstrate that loss of polarity proteins confers phenotypic plasticity to epithelial cells such that they display normal behavior under normal culture conditions but display aggressive behavior in response to activation of oncogenes or exposure to cytokines.

Early lethality, functional NF-kappaB activation, and increased sensitivity to TNF-induced cell death in TRAF2-deficient mice

TRAF2 is an intracellular signal-transducing protein recruited to the TNFR1 and TNFR2 receptors following TNF stimulation. To investigate the physiological role of TRAF2, we generated TRAF2-deficient mice. traf2-/- mice appeared normal at birth but became progressively runted and died prematurely. Atrophy of the thymus and spleen and depletion of B cell precursors also were observed. Thymocytes and other hematopoietic progenitors were highly sensitive to TNF-induced cell death and serum TNF levels were elevated in these TRAF2-deficient animals. Examination of traf2-/- cells revealed a severe reduction in TNF-mediated JNK/SAPK activation but a mild effect on NF-kappaB activation. These results suggest that TRAF2-independent pathways of NF-kappaB activation exist and that TRAF2 is required for an NF-kappaB-independent signal that protects against TNF-induced apoptosis.

T cell development in mice expressing splice variants of the protein tyrosine phosphatase CD45

The transmembrane protein tyrosine phosphatase CD45 is expressed in multiple isoforms as a result of alternative splicing of variable exons encoding the extracellular domain. CD45 expression is critical for T cell development, and thymocyte maturation is blocked at the immature CD4+ CD8+ double-positive stage in CD45 gene-deficient (CD45 -/-) mice. Moreover, splicing of variable CD45 exons changes during thymocyte selection. To test the role of CD45 extracellular splice variants in T cell selection and development, we introduced CD45RO (a low-m.w. splice variant lacking exons 4, 5, and 6) and CD45ABC (a high-m.w. isoform containing all exons) transgenes under the control of a thymocyte-specific promoter into a CD45 -/- background, generating CD45RO transgene-positive CD45 -/- (CD45RO) and CD45ABC transgene-positive CD45 -/- (CD45ABC) mice. We demonstrate that both CD45 splice isoforms can rescue development of CD4+ and CD8+ TCR-alphabeta+ thymocytes. Neither CD45 isoform rescued positive selection of H-Y TCR transgene thymocytes, and these cells were blocked at a HSA(high) CD69- CD5(low) stage of development. Peripheral T cells from CD45RO and CD45ABC mice proliferated in response to allogeneic stimulator cells and anti-CD3epsilon cross-linking. However, only CD45RO mice, not CD45ABC mice, generated cytotoxic T cell responses and neutralizing, Th cell-dependent IgG Abs after viral infections. In addition, we show that T cells from CD45RO and CD45ABC mice accumulate in lymph nodes but not in the spleen, liver, or skin, indicating that the CD45 phosphatase may control the homing behavior and trafficking of T cells.

T cell development in mice expressing splice variants of the protein tyrosine phosphatase CD45

The transmembrane protein tyrosine phosphatase CD45 is expressed in multiple isoforms as a result of alternative splicing of variable exons encoding the extracellular domain. CD45 expression is critical for T cell development, and thymocyte maturation is blocked at the immature CD4+ CD8+ double-positive stage in CD45 gene-deficient (CD45 -/-) mice. Moreover, splicing of variable CD45 exons changes during thymocyte selection. To test the role of CD45 extracellular splice variants in T cell selection and development, we introduced CD45RO (a low-m.w. splice variant lacking exons 4, 5, and 6) and CD45ABC (a high-m.w. isoform containing all exons) transgenes under the control of a thymocyte-specific promoter into a CD45 -/- background, generating CD45RO transgene-positive CD45 -/- (CD45RO) and CD45ABC transgene-positive CD45 -/- (CD45ABC) mice. We demonstrate that both CD45 splice isoforms can rescue development of CD4+ and CD8+ TCR-alphabeta+ thymocytes. Neither CD45 isoform rescued positive selection of H-Y TCR transgene thymocytes, and these cells were blocked at a HSA(high) CD69- CD5(low) stage of development. Peripheral T cells from CD45RO and CD45ABC mice proliferated in response to allogeneic stimulator cells and anti-CD3epsilon cross-linking. However, only CD45RO mice, not CD45ABC mice, generated cytotoxic T cell responses and neutralizing, Th cell-dependent IgG Abs after viral infections. In addition, we show that T cells from CD45RO and CD45ABC mice accumulate in lymph nodes but not in the spleen, liver, or skin, indicating that the CD45 phosphatase may control the homing behavior and trafficking of T cells.

Impaired negative selection of T cells in Hodgkin's disease antigen CD30-deficient mice

CD30 is found on Reed-Sternberg cells of Hodgkin's disease and on a variety of non-Hodgkin's lymphoma cells and is up-regulated on cells after Epstein-Barr virus, human T cell leukemia virus, and HIV infections. We report here that the thymus in CD30-deficient mice contains elevated numbers of thymocytes. Activation-induced death of thymocytes after CD3 cross-linking is impaired both in vitro and in vivo. Breeding the CD30 mutation separately into alpha beta TCR-or gamma delta TCR-transgenic mice revealed a gross defect in negative but not positive selection. Thus, like TNF-receptors and Fas/Apo-1, the CD30 receptor is involved in cell death signaling. It is also an important coreceptor that participates in thymic deletion.

Expression of a tumor necrosis factor alpha transgene in murine pancreatic beta cells results in severe and permanent insulitis without evolution towards diabetes

Mice bearing a tumor necrosis factor (TNF) alpha transgene controlled by an insulin promoter developed an increasingly severe lymphocytic insulitis, apparently resulting from the induction of endothelial changes with features similar to those observed in other places of intense lymphocytic traffic. This was accompanied by dissociation of the endocrine tissue (without marked decrease in its total mass), islet fibrosis, and the development of intraislet ductules containing, by places, beta cells in their walls, suggesting a regenerative capacity. Islet disorganization and fibrosis did not result from lymphocytic infiltration, since they were also observed in SCID mice bearing the transgene. Diabetes never developed, even though a number of potentially inducing conditions were used, including the prolonged perfusion of interferon gamma and the permanent expression of a nontolerogenic viral protein on beta cells (obtained by using mice bearing two transgenes). It is concluded that (a) a slow process of TNF release in pancreatic islets induces insulitis, and may be instrumental in the insulitis resulting from local cell-mediated immune reactions, but (b) that insulitis per se is not diabetogenic, lymphocyte stimulation by cells other than beta cells being necessary to trigger extensive beta cell damage. This provides an explanation for the discrepancy between the occurrence of insulitis and that of clinical disease in autoimmune diabetes.

A cortisone sensitive CD3low subset of CD4+CD8- thymocytes represents an intermediate stage in intrathymic repertoire selection

Two populations of CD4 single positive (SP) thymocytes were found in transgenic mice bearing class I-restricted Mls-1a reactive (V beta 8.1) TCR genes in the absence of the restriction element. CD3high CD4 SP cells were deleted in the presence of Mls-1a and were cortisone resistant, whereas CD3low CD4 SP cells were not deleted in the presence of Mls-1a and were cortisone sensitive. Intravenous transfer of CD3low CD4 SP cells into nude mice resulted in significant peripheral expansion of these cells with apparent upregulation of CD3. These data indicate that CD3low CD4 SP thymocytes represent an intermediate stage in the transition from CD3low double positive (DP) to CD3high SP thymocytes and raise the possibility that these cells may hve undergone positive but not negative selection events (at least to Mls-1a). Furthermore the fact that CD3high DP thymocytes were also deleted by Mls-1a in these mice suggests strongly that sensitivity to Mls-1a deletion is dependent upon stage of thymic maturation (as revealed by TCR density) rather than CD4/CD8 phenotype.

Analysis of immature (CD4-CD8-) thymic subsets in T-cell receptor alpha beta transgenic mice

Introduction of a transgenic alpha beta TCR (V alpha 2, V beta 8.1) specific for lymphocytic choriomeningitis virus (LCMV), in the context of H-2Db into the genome of C57BL/6 mice, has many effects on the development and selection of T cells in both the thymus and the periphery. These mice produce increased numbers of CD4-8+ mature T cells, all of which express the transgenic TCR, and small numbers of CD4+8- cells using endogenous TCRs are also produced. This study follows the intrathymic development of T cells in these TCR alpha beta transgenic mice, in particular the earliest CD4-8- stages. As expected, the transgenic TCR is expressed on the cell surface at an earlier developmental stage than endogenous TCRs in nontransgenic littermate controls. Of the three major subsets expressing the heat-stable antigen (HSA), only the most mature, the CD25-CD44- expresses the transgenic TCR, and the earlier CD25-CD44+ and CD25+CD44- do not. Furthermore, in contrast to other TCR alpha beta transgenic lines, TCR gamma delta lineage cells appear to develop normally.

T and B cell tolerance and responses to viral antigens in transgenic mice: implications for the pathogenesis of autoimmune versus immunopathological disease

Experiments with transgenic mice illustrate clonal elimination of T cells specific for antigens expressed appropriately in the thymus, but presence of inducible T cells when the antigen presented on class I MHC antigens is expressed exclusively on non-lymphohemopoietic cells in the periphery (pancreatic beta islet cells). TCR-transgenic LCMV-carrier mice expressing LCMV in the thymus exhibit clonal elimination at the early CD4+8+ thymocyte stage, causing CTL unresponsiveness in these mice. In contrast, studies with RIP LCMV-GP-transgenic mice (expressing GP in pancreatic beta cells) and with TCR-RIP LCMV-GP double-transgenic mice show that CTL reactivity is normal. These experiments argue against so-called peripheral anergy of class I MHC antigen-restricted cytotoxic T cells as a general mechanism of peripheral immunological tolerance to self. They reveal that self epitopes that are genetically self and presented by class I antigens may not be considered immunologically self if expressed solely extrathymically, despite the fact that they are antigenic and can be recognized by induced effector T cells. Genetic self that is presented on cells which can induce neither tolerance nor an immune response is immunologically dealt with as foreign and therefore may be called nonimmunological self. Appropriate presentation of the same epitope on antigen-presenting cells promptly induces effector T cells and causes disease; such disease should not be called autoimmune because it is an immunopathological T-cell mediated disease, comparable to an unfavorably balanced immunopathological T-cell response to a virus. Mechanisms that control autoantibody responses were studied in mice expressing a viral transgene. Such mice generate neutralizing antiviral autoantibody responses only when the transgenic viral antigen is linked to a foreign T-helper determinant. These findings, therefore, document differences in levels of T- vs B-cell tolerance (so-called split tolerance) under a given expression level of a "self" antigen. They illustrate how unresponsiveness of B cells to produce T-independent IgM is dose-dependent and that IgG autoantibodies are triggered by introducing foreign T-helper determinants that can be recognised in a linked fashion. This model suggests that, while T-cell tolerance to tolerogenic self in the thymus is solid, B-cell tolerance in general is not. From the point of view of autoantibody responses these T-helper cells may also be called immunopathological; i.e., these T-helper cells are specific for foreign epitopes that, via linked recognition, trigger truly autoimmune B cells.(ABSTRACT TRUNCATED AT 400 WORDS)

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.