RESUMO
Invariant natural killer T cell (iNKT) subsets are differentially distributed in various immune organs. However, it remains unclear whether iNKT cells exhibit phenotypical and functional differences in different peripheral organs and how thymic iNKT cells emigrate to peripheral organs. Here, we used single-cell RNA-seq to map iNKT cells from peripheral organs. iNKT1 cells from liver, spleen, and lymph node appear to have distinct phenotypic profiles and functional capabilities. However, iNKT17 transcriptomes were comparable across peripheral organs. In addition, by integrating data with a thymic iNKT cell study, we uncovered a transient population of recent thymic emigrants, a cluster of peripheral iNKT cells with high expression of transcription factor Kruppel-like factor 2 (Klf2). Deletion of Klf2 led to a severe impairment of iNKT differentiation and migration. Our study revealed that iNKT subsets are uniquely distributed in peripheral organs with some inter-local tissue variation, especially for iNKT1 cell, and identified Klf2 as a rheostat for iNKT cell migration and differentiation.
RESUMO
The class III PI3K Vacuolar protein sorting 34 (Vps34) plays a role in both canonical and noncanonical autophagy, key processes that control the presentation of antigens by dendritic cells (DCs) to naive T lymphocytes. We generated DC-specific Vps34-deficient mice to assess the contribution of Vps34 to DC functions. We found that DCs from these animals have a partially activated phenotype, spontaneously produce cytokines, and exhibit enhanced activity of the classic MHC class I and class II antigen-presentation pathways. Surprisingly, these animals displayed a defect in the homeostatic maintenance of splenic CD8α+ DCs and in the capacity of these cells to cross-present cell corpse-associated antigens to MHC class I-restricted T cells, a property that was associated with defective expression of the T-cell Ig mucin (TIM)-4 receptor. Importantly, mice deficient in the Vps34-associated protein Rubicon, which is critical for a noncanonical form of autophagy called "Light-chain 3 (LC3)-associated phagocytosis" (LAP), lacked such defects. Finally, consistent with their defect in the cross-presentation of apoptotic cells, DC-specific Vps34-deficient animals developed increased metastases in response to challenge with B16 melanoma cells. Collectively, our studies have revealed a critical role of Vps34 in the regulation of CD8α+ DC homeostasis and in the capacity of these cells to process and present antigens associated with apoptotic cells to MHC class I-restricted T cells. Our findings also have important implications for the development of small-molecule inhibitors of Vps34 for therapeutic purposes.
Assuntos
Apresentação de Antígeno/imunologia , Autofagia/imunologia , Linfócitos T CD8-Positivos/imunologia , Classe III de Fosfatidilinositol 3-Quinases/genética , Apresentação Cruzada/imunologia , Células Dendríticas/imunologia , Animais , Apresentação de Antígeno/genética , Autofagia/genética , Proteínas Relacionadas à Autofagia/genética , Proteínas Relacionadas à Autofagia/metabolismo , Antígenos CD8/metabolismo , Células Cultivadas , Classe III de Fosfatidilinositol 3-Quinases/metabolismo , Apresentação Cruzada/genética , Citocinas/imunologia , Endocitose/fisiologia , Antígenos de Histocompatibilidade Classe I/imunologia , Melanoma Experimental/patologia , Proteínas de Membrana/biossíntese , Camundongos , Camundongos Knockout , Fagocitose/fisiologiaRESUMO
The nature and anatomic location of the protective memory CD8(+) T cell subset induced by intranasal vaccination remain poorly understood. We developed a vaccination model to assess the anatomic location of protective memory CD8(+) T cells and their role in lower airway infections. Memory CD8(+) T cells elicited by local intranasal, but not systemic, vaccination with an engineered non-replicative CD8(+) T cell-targeted antigen confer enhanced protection to a lethal respiratory viral challenge. This protection depends on a distinct CXCR3(LO) resident memory CD8(+) T (Trm) cell population that preferentially localizes to the pulmonary interstitium. Because they are positioned close to the mucosa, where infection occurs, interstitial Trm cells act before inflammation can recruit circulating memory CD8(+) T cells into the lung tissue. This results in a local protective immune response as early as 1 day post-infection. Hence, vaccine strategies that induce lung interstitial Trm cells may confer better protection against respiratory pathogens.
Assuntos
Antígenos Virais/imunologia , Linfócitos T CD8-Positivos/imunologia , Memória Imunológica , Infecções Respiratórias/prevenção & controle , Vacínia/prevenção & controle , Vacinas Virais/administração & dosagem , Administração Intranasal , Sequência de Aminoácidos , Animais , Antígenos Virais/química , Peso Corporal/efeitos dos fármacos , Linfócitos T CD8-Positivos/virologia , Expressão Gênica , Imunidade nas Mucosas/efeitos dos fármacos , Imunofenotipagem , Pulmão/efeitos dos fármacos , Pulmão/imunologia , Pulmão/virologia , Camundongos , Camundongos Transgênicos , Receptores CXCR3/genética , Receptores CXCR3/imunologia , Infecções Respiratórias/imunologia , Infecções Respiratórias/patologia , Infecções Respiratórias/virologia , Vacinação , Vacínia/imunologia , Vacínia/patologia , Vacínia/virologia , Vaccinia virus/química , Vaccinia virus/efeitos dos fármacos , Vaccinia virus/crescimento & desenvolvimento , Vaccinia virus/patogenicidade , Carga Viral/efeitos dos fármacos , Vacinas Virais/biossínteseRESUMO
Tregs are essential for maintaining peripheral tolerance, and thus targeting these cells may aid in the treatment of autoimmunity and cancer by enhancing or reducing suppressive functions, respectively. Before these cells can be harnessed for therapeutic purposes, it is necessary to understand how they maintain tolerance under physiologically relevant conditions. We now report that transcription factor Kruppel-like factor 2 (KLF2) controls naive Treg migration patterns via regulation of homeostatic and inflammatory homing receptors, and that in its absence KLF2-deficient Tregs are unable to migrate efficiently to secondary lymphoid organs (SLOs). Diminished Treg trafficking to SLOs is sufficient to initiate autoimmunity, indicating that SLOs are a primary site for maintaining peripheral tolerance under homeostatic conditions. Disease severity correlates with impaired Treg recruitment to SLOs and, conversely, promotion of Tregs into these tissues can ameliorate autoimmunity. Moreover, stabilizing KLF2 expression within the Treg compartment enhances peripheral tolerance by diverting these suppressive cells from tertiary tissues into SLOs. Taken together, these results demonstrate that peripheral tolerance is enhanced or diminished through modulation of Treg trafficking to SLOs, a process that can be controlled by adjusting KLF2 protein levels.
Assuntos
Tolerância Imunológica , Fatores de Transcrição Kruppel-Like/fisiologia , Linfócitos T Reguladores/fisiologia , Animais , Autoimunidade , Movimento Celular , Tecido Linfoide/imunologia , Camundongos , Receptores de Retorno de Linfócitos/fisiologiaRESUMO
Natural killer (NK) cells are innate lymphocytes that recognize and lyse virally infected or transformed cells. This latter property is being pursued in clinics to treat leukemia with the hope that further breakthroughs in NK cell biology can extend treatments to other cancers. At issue is the ability to expand transferred NK cells and prolong their functionality within the context of a tumor. In terms of NK cell expansion and survival, we now report that Kruppel-like factor 2 (KLF2) is a key transcription factor that underpins both of these events. Excision of Klf2 using gene-targeted mouse models promotes spontaneous proliferation of immature NK cells in peripheral tissues, a phenotype that is replicated under ex vivo conditions. Moreover, KLF2 imprints a homeostatic migration pattern on mature NK cells that allows these cells to access IL-15-rich microenvironments. KLF2 accomplishes this feat within the mature NK cell lineage via regulation of a subset of homing receptors that respond to homeostatic ligands while leaving constitutively expressed receptors that recognize inflammatory cytokines unperturbed. Under steady-state conditions, KLF2-deficient NK cells alter their expression of homeostatic homing receptors and subsequently undergo apoptosis due to IL-15 starvation. This novel mechanism has implications regarding NK cell contraction following the termination of immune responses including the possibility that retention of an IL-15 transpresenting support system is key to extending NK cell activity in a tumor environment.
Assuntos
Proliferação de Células/fisiologia , Sobrevivência Celular/fisiologia , Interleucina-15/metabolismo , Células Matadoras Naturais/citologia , Células Matadoras Naturais/fisiologia , Fatores de Transcrição Kruppel-Like/metabolismo , Animais , Células Cultivadas , Regulação da Expressão Gênica/fisiologia , Homeostase/fisiologia , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Regulatory T cells (Tregs) are a specialized subset of CD4(+) T cells that maintain self-tolerance by functionally suppressing autoreactive lymphocytes. The Treg compartment is composed of thymus-derived Tregs (tTregs) and peripheral Tregs (pTregs) that are generated in secondary lymphoid organs after exposure to antigen and specific cytokines, such as TGF-ß. With regard to this latter lineage, pTregs [and their ex vivo generated counterparts, induced Tregs (iTregs)] offer particular therapeutic potential because these cells can be raised against specific antigens to limit autoimmunity. We now report that transcription factor Krüppel-like factor 2 (KLF2) is necessary for the generation of iTregs but not tTregs. Moreover, drugs that limit KLF2 proteolysis during T-cell activation enhance iTreg development. To the authors' knowledge, this study identifies the first transcription factor to distinguish between i/pTreg and tTreg ontogeny and demonstrates that KLF2 is a therapeutic target for the production of regulatory T cells.
Assuntos
Autoimunidade/imunologia , Diferenciação Celular/imunologia , Fatores de Transcrição Kruppel-Like/metabolismo , Linfócitos T Reguladores/imunologia , Animais , Autoimunidade/genética , Imunoprecipitação da Cromatina , Primers do DNA/genética , Citometria de Fluxo , Fatores de Transcrição Kruppel-Like/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos TransgênicosRESUMO
Follicular (FO) and marginal zone (MZ) B cells are maintained in distinct locations within the spleen, but the genetic basis for this separation is still enigmatic. We now report that B cell sequestration requires lineage-specific regulation of migratory receptors by the transcription factor Klf2. Moreover, using gene-targeted mice we show that altered splenic B cell migration confers a significant in vivo gain-of-function phenotype to FO B cells, including the ability to quickly respond to MZ-associated antigens and pathogens in a T cell-dependent manner. This work demonstrates that in wild-type animals, naive FO B cells are actively removed from the MZ, thus restricting their capacity to respond to blood-borne pathogens.
Assuntos
Linfócitos B/citologia , Linfócitos B/imunologia , Movimento Celular , Imunidade Humoral , Baço/citologia , Baço/imunologia , Animais , Antígenos CD19/genética , Antígenos CD19/imunologia , Antígenos T-Independentes/genética , Antígenos T-Independentes/imunologia , Medula Óssea/imunologia , Diferenciação Celular , Células Cultivadas , Fatores de Transcrição Kruppel-Like/deficiência , Fatores de Transcrição Kruppel-Like/imunologia , Camundongos , Camundongos Knockout , Receptores CCR/imunologiaRESUMO
Although platelets appear by embryonic day 10.5 in the developing mouse, an embryonic role for these cells has not been identified. The SYK-SLP-76 signaling pathway is required in blood cells to regulate embryonic blood-lymphatic vascular separation, but the cell type and molecular mechanism underlying this regulatory pathway are not known. In the present study we demonstrate that platelets regulate lymphatic vascular development by directly interacting with lymphatic endothelial cells through C-type lectin-like receptor 2 (CLEC-2) receptors. PODOPLANIN (PDPN), a transmembrane protein expressed on the surface of lymphatic endothelial cells, is required in nonhematopoietic cells for blood-lymphatic separation. Genetic loss of the PDPN receptor CLEC-2 ablates PDPN binding by platelets and confers embryonic lymphatic vascular defects like those seen in animals lacking PDPN or SLP-76. Platelet factor 4-Cre-mediated deletion of Slp-76 is sufficient to confer lymphatic vascular defects, identifying platelets as the cell type in which SLP-76 signaling is required to regulate lymphatic vascular development. Consistent with these genetic findings, we observe SLP-76-dependent platelet aggregate formation on the surface of lymphatic endothelial cells in vivo and ex vivo. These studies identify a nonhemostatic pathway in which platelet CLEC-2 receptors bind lymphatic endothelial PDPN and activate SLP-76 signaling to regulate embryonic vascular development.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Plaquetas/fisiologia , Lectinas Tipo C/fisiologia , Vasos Linfáticos/embriologia , Vasos Linfáticos/fisiologia , Fosfoproteínas/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Plaquetas/metabolismo , Vasos Sanguíneos/metabolismo , Células Cultivadas , Embrião de Mamíferos , Células Endoteliais/metabolismo , Células Endoteliais/fisiologia , Endotélio Linfático/embriologia , Endotélio Linfático/metabolismo , Endotélio Vascular/embriologia , Endotélio Vascular/metabolismo , Humanos , Lectinas Tipo C/genética , Lectinas Tipo C/metabolismo , Vasos Linfáticos/metabolismo , Glicoproteínas de Membrana/metabolismo , Glicoproteínas de Membrana/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Ligação Proteica , Transdução de Sinais/genética , Transdução de Sinais/fisiologiaRESUMO
The migration patterns of naive and activated T cells are associated with the expression of distinct sets of chemokine receptors, but the molecular basis for this regulation is unknown. Here we identify Krupple-like factor 2 (KLF2) as a key transcriptional factor needed to prevent naive T cells from expressing inflammatory chemokine receptors and acquiring the migration patterns of activated T cells. Lineage-specific deletion of KLF2 resulted in fewer naive T cells in the blood and secondary lymphoid organs, whereas it expanded naive T cell numbers in nonlymphoid tissues; these effects were associated with altered expression of inflammatory chemokine receptors on naive T cells. KLF2 repressed the expression of several chemokine receptors, including CCR3 and CCR5. We thus conclude that KLF2 maintains proper T cell migration patterns by linking T cell movement and transcriptional regulation of chemokine receptor expression patterns.
Assuntos
Linfócitos T CD4-Positivos/imunologia , Movimento Celular/imunologia , Regulação da Expressão Gênica/imunologia , Fatores de Transcrição Kruppel-Like/fisiologia , Receptores CCR3/metabolismo , Receptores CCR5/metabolismo , Animais , Fatores de Transcrição Kruppel-Like/genética , Ativação Linfocitária/imunologia , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Reação em Cadeia da Polimerase , RNA Mensageiro/biossíntese , Receptores CCR3/genética , Receptores CCR5/genéticaRESUMO
Hemodynamic responses that control blood pressure and the distribution of blood flow to different organs are essential for survival. Shear forces generated by blood flow regulate hemodynamic responses, but the molecular and genetic basis for such regulation is not known. The transcription factor KLF2 is activated by fluid shear stress in cultured endothelial cells, where it regulates a large number of vasoactive endothelial genes. Here, we show that Klf2 expression during development mirrors the rise of fluid shear forces, and that endothelial loss of Klf2 results in lethal embryonic heart failure due to a high-cardiac-output state. Klf2 deficiency does not result in anemia or structural vascular defects, and it can be rescued by administration of phenylephrine, a catecholamine that raises vessel tone. These findings identify Klf2 as an essential hemodynamic regulator in vivo and suggest that hemodynamic regulation in response to fluid shear stress is required for cardiovascular development and function.
Assuntos
Vasos Sanguíneos/fisiologia , Endotélio Vascular/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Insuficiência Cardíaca , Fatores de Transcrição Kruppel-Like/fisiologia , Anemia/fisiopatologia , Animais , Malformações Arteriovenosas/fisiopatologia , Velocidade do Fluxo Sanguíneo , Vasos Sanguíneos/citologia , Vasos Sanguíneos/efeitos dos fármacos , Células Cultivadas , Embrião de Mamíferos/citologia , Embrião de Mamíferos/metabolismo , Embrião não Mamífero , Endotélio Vascular/citologia , Endotélio Vascular/efeitos dos fármacos , Genes Letais , Integrases/metabolismo , Fatores de Transcrição Kruppel-Like/genética , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Proteínas dos Microfilamentos/genética , Proteínas dos Microfilamentos/fisiologia , Proteínas Musculares/genética , Proteínas Musculares/fisiologia , Músculo Liso/citologia , Músculo Liso/efeitos dos fármacos , Músculo Liso/metabolismo , Miocárdio/citologia , Miocárdio/metabolismo , Fenilefrina/farmacologia , Reação em Cadeia da Polimerase , Regiões Promotoras Genéticas , Receptor TIE-2/genética , Receptor TIE-2/fisiologia , Estresse Mecânico , Transcrição Gênica , Veias Umbilicais/citologia , Veias Umbilicais/efeitos dos fármacos , Veias Umbilicais/metabolismo , Peixe-Zebra/embriologia , Peixe-Zebra/metabolismoRESUMO
Syk tyrosine kinase and Src homology 2 (SH2) domain-containing leukocyte-specific phosphoprotein of 76 kDa (SLP-76) are signaling mediators activated downstream of immunoreceptor tyrosine-based activation motif (ITAM)-containing immunoreceptors and integrins. While the signaling cascades descending from integrins are similar to immunoreceptors, the mechanism of Syk activation and SLP-76 recruitment remains unclear. We used an in vivo structure-function approach to study the requirements for the domains of Syk and SLP-76 in immunoreceptor and integrin signaling. We found that both SH2 domains and the kinase domain of Syk are required for immunoreceptor-dependent signaling and cellular response via integrins. While the Gads-binding domain of SLP-76 is needed for immunoreceptor signaling, it appears dispensable for integrin signaling. Syk and SLP-76 also are required for initiating and/or maintaining separation between the blood and lymphatic vasculature. Therefore, we correlated the signaling requirement of the various domains of Syk and SLP-76 to their requirement in regulating vascular separation. Our data suggest ITAMs are required in Syk-dependent integrin signaling, demonstrate the separation of the structural features of SLP-76 to selectively support immunoreceptor versus integrin signaling, and provide evidence that the essential domains of SLP-76 for ITAM signals are those which most efficiently support separation between lymphatic and blood vessels.
Assuntos
Sistema Hematopoético/citologia , Sistema Hematopoético/metabolismo , Integrinas/metabolismo , Fosfoproteínas/metabolismo , Transdução de Sinais , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Vasos Sanguíneos/citologia , Vasos Sanguíneos/patologia , Vasos Sanguíneos/fisiologia , Células CHO , Membrana Celular/metabolismo , Células Cultivadas , Cricetinae , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/deficiência , Camundongos , Mutação/genética , Fosfoproteínas/deficiência , Fosfotirosina/metabolismo , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas Tirosina Quinases/deficiência , Receptores Imunológicos/metabolismo , Quinase Syk , Domínios de Homologia de srcRESUMO
Developmental studies support a common origin for blood and endothelial cells, while studies of adult angiogenic responses suggest that the hematopoietic system can be a source of endothelial cells later in life. Whether hematopoietic tissue is a source of endothelial cells during normal vascular development is unknown. Mouse embryos lacking the signaling proteins Syk and Slp-76 develop abnormal blood-lymphatic endothelial connections. Here we demonstrate that expression of GFPSlp-76 in a subset of hematopoietic cells rescues this phenotype, and that deficient cells confer focal vascular phenotypes in chimeric embryos consistent with a cell-autonomous mechanism. Endogenous Syk and Slp-76, as well as transgenic GFPSlp-76, are expressed in circulating cells previously proposed to be endothelial precursors, supporting a causal role for these cells. These studies provide genetic evidence for hematopoietic contribution to vascular development and suggest that hematopoietic tissue can provide a source of vascular endothelial progenitor cells throughout life.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Endotélio Vascular/fisiologia , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Neovascularização Fisiológica , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Proteínas Tirosina Quinases/genética , Proteínas Tirosina Quinases/metabolismo , Animais , Biomarcadores/análise , Plaquetas/metabolismo , Vasos Sanguíneos , Células Endoteliais/metabolismo , Fator de Transcrição GATA1/genética , Sistema Hematopoético/embriologia , Sistema Hematopoético/metabolismo , Tecido Linfoide/metabolismo , Camundongos , Camundongos Transgênicos , Modelos Biológicos , Neutrófilos/metabolismo , Quinase SykRESUMO
Integrins are heterodimeric adhesion receptors associated with bidirectional signaling. In vitro studies support a role for the binding of evolutionarily conserved tyrosine motifs (NPxY) in the beta integrin cytoplasmic tail to phosphotyrosine-binding (PTB) domain-containing proteins, an interaction proposed to be dynamically regulated by tyrosine phosphorylation. Here we show that replacement of both beta1 integrin cytoplasmic tyrosines with alanines, resulting in the loss of all PTB domain interaction, causes complete loss of beta1 integrin function in vivo. In contrast, replacement of beta1 integrin cytoplasmic tyrosines with phenylalanines, a mutation that prevents tyrosine phosphorylation, conserves in vivo integrin function. These results have important implications for the molecular mechanism and regulation of integrin function.
Assuntos
Citoplasma/metabolismo , Integrina beta1/fisiologia , Tirosina/fisiologia , Motivos de Aminoácidos , Animais , Sequência de Bases , Primers do DNA , Integrina beta1/química , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , FosforilaçãoRESUMO
Lymphatic vessels develop from specialized endothelial cells in preexisting blood vessels, but the molecular signals that regulate this separation are unknown. Here we identify a failure to separate emerging lymphatic vessels from blood vessels in mice lacking the hematopoietic signaling protein SLP-76 or Syk. Blood-lymphatic connections lead to embryonic hemorrhage and arteriovenous shunting. Expression of slp-76 could not be detected in endothelial cells, and blood-filled lymphatics also arose in wild-type mice reconstituted with SLP-76-deficient bone marrow. These studies reveal a hematopoietic signaling pathway required for separation of the two major vascular networks in mammals.
Assuntos
Vasos Sanguíneos/embriologia , Precursores Enzimáticos/metabolismo , Fluoresceína-5-Isotiocianato/análogos & derivados , Sistema Linfático/embriologia , Fosfoproteínas/metabolismo , Proteínas Tirosina Quinases/metabolismo , Transdução de Sinais , Proteínas Adaptadoras de Transdução de Sinal , Animais , Animais Recém-Nascidos , Antígenos CD34/metabolismo , Vasos Sanguíneos/anormalidades , Vasos Sanguíneos/citologia , Vasos Sanguíneos/metabolismo , Células da Medula Óssea/citologia , Células da Medula Óssea/fisiologia , Transplante de Medula Óssea , Dextranos , Endotélio Linfático/citologia , Endotélio Linfático/metabolismo , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Precursores Enzimáticos/genética , Glicoproteínas/metabolismo , Hemorragia , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Intestinos/irrigação sanguínea , Peptídeos e Proteínas de Sinalização Intracelular , Sistema Linfático/anormalidades , Sistema Linfático/citologia , Sistema Linfático/metabolismo , Proteínas de Membrana Transportadoras , Artérias Mesentéricas/anormalidades , Veias Mesentéricas/anormalidades , Camundongos , Fosfoproteínas/genética , Proteínas Tirosina Quinases/genética , Células-Tronco/fisiologia , Quinase Syk , Proteínas Supressoras de Tumor , Receptor 3 de Fatores de Crescimento do Endotélio Vascular/metabolismo , Veias/citologia , Veias/embriologia , Veias/metabolismoRESUMO
T cell receptor (TCR) stimulation activates the small GTPase Rap1A, which is reported to antagonize Ras signaling and induces T cell anergy. To address its role in vivo, we generated transgenic mice that constitutively expressed active Rap1A within the T cell lineage. We found that active Rap1A did not interfere with the Ras signaling pathway or antagonize T cell activation. Instead of anergy, the T lymphocytes that constitutively expressed active Rap1A showed enhanced TCR-mediated responses, both in thymocytes and mature T cells. In addition, Rap1A activation was sufficient to induce strong activation of the beta1 and beta2 integrins via an avidity-modulation mechanism. This shows that, far from playing an inhibitory role during T cell activation, Rap1A positively influences T cells by augmenting lymphocyte responses and directing integrin activation.