<p>Linker for Activation of T cells, LAT, is a transmembrane adaptor protein that is vital for integrating TCR-mediated signals that modulate T cell development, activation, and proliferation. Upon engagement of the T cell receptor, LAT is phosphorylated and associates with Grb2, Gads, and PLC&#947;1 through its four distal tyrosine residues. Mutation of tyrosine 136 abolishes LAT binding to PLC&#947;1. This results in impaired TCR-mediated calcium mobilization and Erk activation. LATY136F knock-in mice have a severe but incomplete block in T cell development. Yet, CD4+ &#945;&#946; T cells undergo uncontrolled expansion in the periphery, resulting in a severe autoimmune syndrome characterized by Th2 skewing and resultant B cell autoreactivity. Here, we further studied the role of LAT-PLC&#947;1 signaling in T cell lineage commitment, cytokine production, and autoimmunity.</p><p>First, we investigated the importance of the LAT-PLC&#947;1 interaction in &#947;&#948; T cells by crossing LATY136F mice with TCR&#946;-deficient mice. Our data showed that the LATY136F mutation had no major effect on the homeostasis of epithelial &#947;&#948; T cells, which could be found in the skin and small intestine. Interestingly, a population of CD4+ &#947;&#948; T cells in the spleen and lymph nodes underwent continuous expansion and produced elevated amounts of IL4, resulting in an autoimmune syndrome similar to that caused by &#945;&#946; T cells in LATY136F mice. Development of these hyperproliferative &#947;&#948; T cells was not dependent on expression of MHC class II or CD4, and their proliferation could be partially suppressed by regulatory T cells. Our data indicated that a unique subset of CD4+ &#947;&#948; T cells could hyperproliferate in LATY136F mice and suggested that LAT-PLC&#947;1 signaling may function differently in various subsets of &#947;&#948; T cells. </p><p>In addition to examining &#947;&#948; and &#945;&#946; T cell development, we also were interested in further exploring the role of LAT in cytokine production. While our previous data have demonstrated that T cells in LATY136F mice are Th2 skewed, producing large amounts of IL4, we investigated other cytokines that may be important for autoimmunity and found that these CD4+ &#945;&#946; T cells could also produce the proinflammatory cytokine IL6. Analysis of whole cell lysates from CD4+ &#945;&#946; LATY136F T cells demonstrated that NF&#954;B, AKT, and p38 were constitutively phosphorylated, and inhibition of these pathways resulted in reduced IL6 production. By crossing LATY136F mice with IL6 deficient mice, we demonstrated that early T cell survival was diminished in the absence of IL6. We further showed that this reduced CD4+ T cell pool was not due to further blocks in development, or an increase in FoxP3+ regulatory T cells. Finally, we demonstrated that over time, CD4+ T cells do hyperproliferate, yet B cell class switching and autoreactivity remains low. Our data uncovered a novel role for LAT-PLC&#947;1 signaling in regulating IL6 production by T cells during autoimmunity. </p><p>Finally, we wanted to further examine IL4 production and T helper cell differentiation in LATY136F mice. We examined IL4 production using KN2 reporter mice, where huCD2 marks T cells that have recently produced IL4 protein. We demonstrated that only a small proportion of the LATY136F T cells were actively secreting IL4. This subset of T cells were Tfh cells that expressed BCL6 and localized to B cell-rich germinal centers within the spleen. Most studies to date have examined Tfh cells in infection models, and have demonstrated that Tfh cells have very low expression of GATA3. Our results revealed in a spontaneous T cell-mediated autoimmune model system, that Tfh cells express both high levels of BCL6 and GATA3. Additionally, using an inducible deletion system, where normal development occurs, we showed that Tfh cells differentiation is the result of aberrant LAT signaling, rather than autoreactive TCRs with high affinity for self-peptide-MHC. LATY136F Tfh cells did require B cells for their development. Together, these results displayed a novel role for tonic LAT-PLC&#947;1 signaling in modulating Tfh cell differentiation and BCL6 expression.</p> / Dissertation

Signalling through antigen specific receptors BCR and TCR is crucial for the development and the function of T cells and B cells. Although much is known about their signalling pathways a number of observations still remain to be clarified. In my thesis, I focused on the roles of Src-family kinases (SFKs) in the initiation of BCR- and TCR-mediated signalling. Several studies have suggested that in contrast to TCR signalling, BCR signal transduction could be initiated independently of SFKs or with only a minimal activity of these kinases. We used genetic approach to study the differences between TCR and BCR signalling apparatuses combined with inhibition of SFKs by pharmacological approach. Using this experimental set up, we show that the differences in the roles of SFKs and in the activities of SFKs needed for the initiation of BCR and TCR signalling are likely based on different composition or architecture of BCR and TCR. We further show that the SFK activity required for the initiation of TCR signalling is lower if ZAP-70 kinase is substituted with Syk kinase, which most likely reflects the different molecular mechanisms of Syk and ZAP-70 kinase activation. Key words: Src-family kinases, BCR receptor, TCR receptor, PP2, B cells, T cells, BCR signalling, TCR signalling.

Les rafts lipidiques sont des nanodomaines membranaires enrichis en cholestérol et en sphingolipides impliqués dans la régulation de la signalisation médiée par le TCR. Néanmoins l'existence et la fonction de ces domaines sont sujettes à controverse compte tenu des difficultés expérimentales pour les étudier in vivo. En utilisant des traitements non invasifs ciblant spécifiquement la voie de biosynthèse de ces lipides, nous avons étudié l'influence de l'organisation latérale de la membrane sur l'activation lymphocytaire T. Par des approches biophysiques, nous avons démontré au sein de lymphocytes T primaires CD4+, que les molécules TCR, CD4 et Lck sont constitutivement partitionnées dans les rafts lipidiques dont est exclue CD45. De plus, cette préorganisation moléculaire modifie les paramètres d'adhésion entre le TCR. Pour étudier le rôle de ces structures au sein de cellules individuelles, nous avons développé une nouvelle méthodologie permettant de détecter et d'analyser à haut débit et de manière automatique la réponse calcique des cellules T. Nous avons confirmé l'influence des rafts membranaires dans la signalisation TCR par les rafts lipidiques joue un rôle majeur dans l'initiation de la reconnaissance antigénique des cellules T. / Lipid rafts are membrane nanodomains enriched in chrolesterol and sphingolipids, which ahave previously been implanted in TCR signaling mechanisms. This contention, however, has beacome highly controversial due to experimental difficulties to study these membrane organizations in vivo. Using non invasive treatments that target specific lipid biosynthesis, we have studied the influence of lateral membrane organization in T lymphocyte activation. By using biophysical approaches, we have demonstrated that in murine CD4+Tcelles, TCR, CD4 and Lck are constitutively and dynamically trapped in lipid rafts, whereas CD45 is excluded. Moreover, this pre-organization impacts binding of TCR to the MHC II-peptide complex and controls the initiation of early TCR signaling. To investigate the role of these structures within individual live cells, we have developed a new high throughput methodology to monitor the calcium mobilization in T cells. We have confirmed the influence of membrane rafts in TCR signaling. Our results have thus demonstrated that pre-organization of TCR signaling protagonists by lipid rafts play a major role in the initiation of T cell antigen recognition

No description available.

The mechanism of T cell recognition is the central but unsolved puzzle of adaptive immunology. The difficulties come from the multichain structure of TCR/CD3, the binate binding structure of the pMHC molecule, the diversity of the peptides presented on the APC, the critical role of coreceptor CD4/8, the communication between TCR and coreceptor CD4/8, the complex environment of interactions taking place and the binding and signaling coupled process of recognition. Most studies were using the 3D kinetic measurements or biological functional assays to address the mechanism of the T cell recognition. However, those assays are usually either lacking of physiology relevance or missing of the initial recognition signals. Here a 2D micropipette adhesion assay with high temporal resolution (-second) was used to address the in situ kinetics of molecular interaction at the membrane of live T cells. The aim of this project is to advance our understanding to the T cell recognition mechanism. The micropipette adhesion assay was firstly used to address a simple case, the resting state pMHC-CD8 interaction. In the absence of TCR-pMHC interaction, the pMHC-CD8 interaction has a very low affinity that depends on the MHC alleles and the lipid rafts of the T cell membrane where CD8 resides, but not on the peptide complexed to the MHC and whether the CD8 is an a a homodimer or an αβ heterodimer. For cognate pMHC, following the initial observation in the F5 T cell system, the binding also displays a two-step curve in the OTI T cell system. The first-step binding occurs before one second and has a very fast on-rate and off-rate (>2s ⁻¹), and the secondstep binding follows immediately but reaches a much higher level of binding. It was identified that the first-step binding is mediated by the TCR-pMHC interaction, and the second-step binding is triggered by the TCR-pMHC interaction but mediated by CD8- pMHC binding. The two-step binding is the unique property of cognate pMHC, and it can be abolished by disrupting the lipid rafts, inhibiting the Src family protein tyrosine kinases (PTK) or protein tyrosine phosphatase (PTP). The finding of two-step binding identifies a CD8-dependent signaling amplification pathway. The data also indicated the active communication between TCR and CD8 in the antigen recognition. The crosstalk between TCR and CD8 was further dissected using two anti-CD8 antibodies 53.6.7 and CT-CD8a. 53-6.7 can significantly enhance the binding of pMHC to the T cell. Although the enhancement is directly mediated by MHC-CD8 interaction, the enhancing role of this antibody is TCR dependent. Blocking the TCR-pMHC interaction on OTI T cell or expressing CD8 alone on a hybridoma abolished the enhancement. The enhancement is also dependent on the integrity of lipid rafts and the normal function of PTP. In contrast, the antibody CT-CD8 can inhibit the binding of pMHC to the T cells and interfere with the TCR-pMHC interaction. The enhancing or inhibitory role of these two anti-CD8 antibodies is reversely correlated with the affinities of TCR-pMHC interactions. Only 53-6.7, but not CT-CD8 antibody, can phosphorylate and activate Lck. The data demonstrated a dual way crosstalk between TCR and CD8, and indicated the importance of cooperation of TCR and CD8 in antigen recognition. In the physiology condition, the TCR must accurately and efficiently recognize the cognate peptide from thousands of surrounding endogenous peptides. There is an argument regarding whether the endogenous peptides plays a role in helping the TCR recognition. Our results demonstrated that the nonstimulatory peptides can significantly enhance the T cell recognition sensitivity. In the presence of nonstimulatory peptide, the TCR can efficiently detect a single antigenic pMHC. The enhancement of recognition is due to the CD8 binding to the nonstimulatory pMHC. Blocking the CD8 binding can paralyze the enhancement. In contrast, it was found that the presence of antagonist can inhibit the binding of agonist pMHC to the T cells, and the inhibition occurs in the initial recognition step. Based on the data, an "amplification and competition" model was proposed to explain the molecular mechanism of the enhancement and inhibition function of the nonstimulatory and antagonist peptides in the T cell recognition, respectively.

Submitted by MARCELA PETROLINI CAPOBIANCO (mpcapobianco@yahoo.com.br) on 2017-04-24T11:43:11Z No. of bitstreams: 1 TESE MARCELA PETROLINI CAPOBIANCO.pdf: 3177156 bytes, checksum: 6b6af4a4ea15e5048723eabdb0659191 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-04-25T20:25:33Z (GMT) No. of bitstreams: 1 capobianco_mp_dr_sjrp.pdf: 3177156 bytes, checksum: 6b6af4a4ea15e5048723eabdb0659191 (MD5) / Made available in DSpace on 2017-04-25T20:25:33Z (GMT). No. of bitstreams: 1 capobianco_mp_dr_sjrp.pdf: 3177156 bytes, checksum: 6b6af4a4ea15e5048723eabdb0659191 (MD5) Previous issue date: 2017-04-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No Brasil o Plasmodium vivax é a espécie mais prevalente, responsável por aproximadamente 85% dos casos de malária. Ademais as variantes da proteína circumesporozoíta (CSP - VK210, VK247 e P. vivax-like) já foram identificadas em várias áreas endêmicas no país. Diversos estudos analisando a influência da variabilidade genética de receptores celulares e moléculas envolvidas na resposta imune, com diferentes peptídeos do Plasmodium, têm obtido resultados variáveis de acordo com o antígeno utilizado e a população analisada. Este trabalho apresenta resultados sobre o estudo de polimorfismos genéticos no TCR (T cell Receptor) e nas Interleucinas 1 e 2 em pacientes infectados por P. vivax provenientes do município de Goianésia do Pará, no Estado do Pará. Avaliou-se estes polimorfismos com a parasitemia do indivíduo, com os genótipos da CSP e com a resposta sorológica contra os peptídeos da CSP. Foram relacionados também estes polimorfismos com os níveis de citocinas. Os polimorfismos foram analisados por técnicas de PCR-RFLP e PCR alelo específico. As análises sorológicas da CSP foram realizadas por ELISA. Foram comparadas as frequências genotípicas observadas segundo o teorema de Hardy-Weinberg (HW). Os níveis de IL1 e IL2 foram avaliados por citometria de fluxo, seguindo protocolo descrito pelo fabricante. Associação dos polimorfismos com os níveis de interleucinas foi avaliada por Análise de variância. As frequências genotípicas e alélicas foram obtidas no programa R v 2.11.1. A parasitemia variou de 15 a 70.000, com mediana de 1.500 parasitos/mm3. Os SNPS investigados mostraram frequências variadas na amostra estudada. Todo o polimorfismo avaliado encontra-se em Equilíbrio de Hard Wenberg. Não houve diferença significativa da parasitemia em relação aos SNPs investigados. Infecções contendo apenas a variante VK247 foram as mais comuns e também não foi observado diferença significativa na resposta de anticorpos de acordo com a variante da CSP presente no momento da infecção. Correlações significativas entre os níveis destas interleucinas com a parasitemia e os níveis de anticorpos contra as variantes da CSP não foram observadas. Além disso, as variantes da CSP não influenciaram os níveis plasmáticos das citocinas e não houve associações positivas entre os SNPs das IL1 e IL2 e seus níveis plasmáticos. Os resultados poderão contribuir na identificação e participação efetiva de genes humanos na modulação da resposta imune, essenciais no estabelecimento de estratégias de imunização contra a doença, em área de transmissão ativa no Estado do Pará. / In Brazil, Plasmodium vivax is the most prevalent species responsible for approximately 85% of malaria cases. In addition, variants of the circosporozoite protein (CSP - VK210, VK247 and P. vivax - like) have already been identified in several endemic areas in the country. Several studies analyzing the influence of the genetic variability of cellular receptors and molecules involved in the immune response with different Plasmodium peptides have obtained variable results according to the antigen used and the analyzed population. This work presents results on the study of genetic polymorphisms in TCR (T cell Receptor) and in Interleukins 1 and 2 in patients infected by P. vivax from the city of Goianésia do Pará, in the State of Pará. These polymorphisms were evaluated with Parasitemia, CSP genotypes and serological response to CSP peptides. These polymorphisms were also related to cytokine levels. Polymorphisms were analyzed by PCR-RFLP and allele-specific PCR techniques. Serological tests of CSP were performed by ELISA. The genotypic frequencies observed according to the Hardy-Weinberg (HW) theorem were compared. Levels of IL1 and IL2 were evaluated by flow cytometry following the protocol described by the manufacturer. Association of polymorphisms with interleukin levels was evaluated by analysis of variance. The genotypic and allelic frequencies were obtained in program R v 2.11.1. The parasitemia ranged from 15 to 70,000, with a median of 1,500 parasites / mm3. The SNPS investigated showed varied frequencies in the sample studied. All polymorphism evaluated is in Hard Wenberg Equilibrium. There was no significant difference in parasitemia in relation to the investigated SNPs. Infections containing only the VK247 variant were the most common and also no significant difference in antibody response was observed according to the CSP variant present at the time of infection. Significant correlations between the levels of these interleukins with parasitemia and levels of antibodies against variants of CSP were not observed. In addition, the CSP variants did not influence plasma cytokine levels and there were no positive associations between IL1 and IL2 SNPs and their plasma levels. The results may contribute to the identification and effective participation of human genes in the modulation of the immune response, essential in the establishment of immunization strategies against the disease, in an active transmission area in the State of Pará.

T cells are an essential component of the adaptive immune system, which evolved to facilitate development of long-term, effective protection against infectious diseases. Upon activation, T cells play an important role in clearing infections, and especially, in preventing establishment of subsequent infections with the same pathogen. Because this is such a powerful response, it must be tightly regulated. Our lab has long been interested in how signaling molecules regulate the function of T and B lymphocytes. Our prior studies stimulated an interest in the signaling adapter molecule, Tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3). Our group previously produced a T cell-conditional (CD4-Cre) TRAF3-/- mouse, which demonstrated that TRAF3 unexpectedly plays an important positive role in T cell functions, including providing help for B cell responses, protection from infectious pathogens, cytokine production and proliferation. After TCR engagement, TRAF3 associates with the T Cell Receptor (TCR)/CD28 complex. These data identified a new role for TRAF3 in T cell activation. There are three signals that are required for full T cell activation. The three types of receptors that deliver these signals are the TCR, co-stimulatory receptors and cytokine receptors. This dissertation explores the regulatory role of TRAF3 in the 3 signals required for T cellsactivation. In signal 1, TRAF3 enhances TCR signaling by regulating the localization of the TCR inhibitors, PTPase non-receptor type 22 (PTPN22) and the c-Src kinase (Csk). Our lab previously reported that recruitment of TRAF3 to the TCR complex requires co-stimulation of CD28, the primary receptor for signal 2. In this dissertation, we show that TRAF3 associates with the Linker of Activated T cells (LAT) complex, demonstrating preference for distinct LAT-associated proteins. For delivery of signal 3, T cells require stimulation of a cytokine receptor, such as IFNαR, for differentiation of a T cell to an effector cell. Upon IFN stimulation, TRAF3 inhibits IFNαR-induced early molecular events, which results in the regulation of both canonical and non-canonical IFNαR signaling pathways. The results presented in this dissertation highlight the dynamic roles of TRAF3 as a regulator of T cell activation, by regulating multiple T cell signaling pathways.

T cells are central regulators of adaptive immunity in infectious and pathophysiological diseases. The activation of T cells is regulated by the T cell antigen receptor (TCR) and co-stimulatory receptors like toll-like receptor 2 (TLR2). These receptors activate distinct and overlapping intracellular signaling pathways that ultimately shape T cell responses. Therefore, studies that elucidate the molecular mechanisms of signal transduction downstream of receptors like the TCR and TLR2 will highlight key pathways required for T cell activation. These pathways could then be clinically targeted to alter dysfunctional T cell responses that promote many human diseases. Focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) are two tyrosine kinases activated by multiple surface receptors expressed on T cells. FAK and Pyk2 signaling regulate cell morphology, migration, adhesion, proliferation, and survival in other cell types. However, their functions in T cells are not well-described. Because FAK and Pyk2 functions are dysregulated in many disease states, it is important to understand their function in human T cells so that clinicians can safely target these kinases to treat various disorders. The studies described in this dissertation aim to more fully elucidate how FAK and Pyk2 control T cell activation mediated by the TCR. We used recombinant microRNAs or kinase inhibitors to transiently suppress FAK and Pyk2's expression or enzymatic function in human T cells. In doing so, several novel functions of FAK and Pyk2 were uncovered. In Chapter III, we revealed that FAK is a negative regulator of TCR signal transduction and function. Interestingly, in contrast to its function in other immune cell lineages, the work described in Chapters III and IV demonstrates that FAK is not required to regulate actin cytoskeletal responses downstream of the TCR. The data presented in Chapter IV demonstrate that Pyk2 regulates TCR-mediated actin cytoskeleton reorganization. This function appears to be linked to Pyk2's scaffolding function and not its enzymatic activity. In Chapter V, we demonstrated that the catalytic function of Pyk2 controls phosphatidylinositol-3-kinase (PI3K) activation in human T cells. Together, these data revealed that FAK and Pyk2 serve distinct functions in TCR signal transduction, actin cytoskeletal rearrangement, and effector responses. TCR-driven cytokine production and proliferation are enhanced when T cells are concurrently activated via TLR2 ligands. In Chapter VI, we describe the signaling pathways that TLR2 activates in human T cells, and we characterize how TCR and TLR2 signals converge to augment T cell responses. In contrast to studies performed using isolated murine T cells, we demonstrated that TLR2 does not activate nuclear-factor kappa B in human T cells. Instead, we found that TCR and TLR2 co-ligation selectively augments extracellular signal-related kinase 1 (Erk1)/Erk2 and Akt activation in human T cells. Thus, TLR2 co-stimulates murine and human T cells via distinct signaling mechanisms.

京都大学 / 新制・課程博士 / 博士(医科学) / 甲第23110号 / 医科博第121号 / 新制||医科||8(附属図書館) / 京都大学大学院医学研究科医科学専攻 / (主査)教授 濵﨑 洋子, 教授 竹内 理, 教授 上野 英樹 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.