These days most everyone can say that they know someone who has been impacted by substance abuse and today’s society is very familiar with the fact that it can wreak havoc on families. There has been a significant amount of research devoted to finding not only the best practices to treat families who are impacted by the disease of addiction but there has also been a great deal of attention focused on the adult perspective on these services once they have been received. Where the research is definitely lacking is how the children involved with the services perceive their own involvement. How are their lives impacted by being involved in treatment with their caretaker? The children seem to be the forgotten voices in this scenario. This study focuses on the adult/child perspective of children who have experienced at least one residential treatment episode with their mothers. The sample came from a long-term residential drug treatment facility that is primary focused on treating families impacted by substance abuse. These adult children experienced treatment with their mothers before they were 12 years old. They will share their perspectives on this experience.

Orientador: Gustavo Maia Souza / Banca: Carlos Henrique Britto de Assis Prado / Banca: Gustavo Habermann / Resumo: A estabilidade é fundamental para todos os sistemas biológicos, possibilitando que lidem com a variabilidade ambiental. As propriedades que conferem estabilidade a sistemas biológicos ainda são desconhecidas, mas evidências apontam para a complexidade da dinâmica de certas variáveis fisiológicas e para a força de interação entre elementos de suas redes organizacionais subjacentes. Esta relação foi investigada no sistema de trocas gasosas de espécies florestais tropicais, pertencentes a grupos funcionais distintos: pioneiras e não-pioneiras. O modelo de recursos múltiplos atribui maior flexibilidade fisiológica às espécies pioneiras, mas os métodos geralmente empregados não são capazes de avaliar a estabilidade de um sistema adequadamente. Este estudo foi realizado em séries temporais de trocas gasosas, onde foi possível estimar parâmetros relacionados à estabilidade do sistema. A força de interação entre elementos foi avaliada pela conectância da rede (Cg) e a complexidade da dinâmica de assimilação de CO2 (A) e condutância estomática (gs) pelo algoritmo de entropia aproximada (ApEn). Os resultados revelaram que espécies com perfil fisiológico de pioneira, em condições constantes, apresentam maior Cg e ApEn de gs, possivelmente indicando maior estabilidade. Estas espécies tiveram maior aproveitamento de pulsos de luz ("lightflecks"), o que indicou a importância da modulação de rede (mudanças na conectância) na resposta às variações ambientais, e que maior Cg pode conferir maior capacidade de controle. Além da conectância, grau de acoplamento do sistema ao ambiente foi decisivo na resposta a "sunflecks". Os resultados sugerem que dinâmicas mais complexas estão ligadas a redes com maior conectância, que por sua vez conferem maior capacidade de controle ao sistema, sendo fundamental a capacidade de modulação da rede. / Abstract: Stability is a key feature to all biological systems, enabling them to deal with environmental variability. The properties that promote stability in biological systems are still unknown, but evidences point towards the complexity of the dynamics of certain physiological variables and to the strength of interaction among elements pertaining to its underlying organizational networks. This relationship was investigated in the gasexchange system of tropical forest species, belonging to distinct functional groups: pioneer and non-pioneer. The multiple resources model attributes higher physiological flexibility to pioneer species, but the methods usually employed are not capable of properly evaluating a system's stability. This study was carried out in gas-exchange time-series, enabling the calculation of parameters related to the system's stability. The strength of interaction among elements was evaluated by network connectance (Cg), and the complexity of CO2 assimilation (A) and stomatal conductance (gs) dynamics was evaluated by the algorithm of Approximate Entropy (ApEn). The results revealed that, under constant conditions, species with a pioneer-like physiological profile showed higher Cg and ApEn of gs, possibly indicating greater stability. These species showed higher lightfleck use efficiency, indicating the importance of network modulation (connectance changes) in response to environmental variability, and that higher Cg could provide greater control capability. Besides connectance, the strength of coupling between system and environment was decisive in response to sunflecks. The results suggest that more complex dynamics are linked to higher network connectance, which provide greater control capability to the system, network modulation being fundamental. Also, higher coupling of the system with its environment apparently promotes stability in contexts where environmental variability occurs within the system's control capability. / Mestre

Despite regulatory efforts of the Occupational Safety and Health Administration (OSHA), 104 cases of nonfatal occupational illnesses and injuries (OIIs) per 10,000 full-time workers required time away from work in 2015. Although OII rates in private and public sectors are high, the rates among state and local government agencies were over 50% higher than private sector rates in 2015, especially in the healthcare industry. OIIs can lead to reduced organizational productivity and performance. Guided by the leader member exchange theory (LMXT) and risk homeostasis theory (RHT), the purpose of this single case study was to explore effective strategies that supervisors in a government agency in the mid-Atlantic region of the United States use to reduce OIIs. Data were collected from face-to-face semistructured interviews with 8 purposefully selected supervisors who had reduced OIIs and the review of company documents. Data were analyzed using inductive coding of phrases, word frequency searches, and theme identification. Four themes emerged: managing employee risk-taking behaviors reduced OIIs, communicating the importance of safety with employees decreased OIIs, having high-quality relationships with employees reduced and mitigated OIIs, and continuous education and training reduced OIIs. Both the LMXT and RHT were essential in exploring the role that education and training played in reducing OIIs. Findings may provide government agencies with valuable information that may lead to a healthier and safer work environment, increased productivity and profitability, and healthier lifestyles inside and outside of the workplace.

Selenium is an essential trace mineral of fundamental importance to human health. Its beneficial functions are largely attributed to its presence within a group of proteins named selenoproteins in the form of the amino acid selenocysteine (Sec). Recently, it was revealed that the human selenoproteome consists of 25 selenoproteins, and for many of them their function remains unknown. The most prominent known roles of selenoproteins are to maintain the intracellular redox homeostasis, redox regulation of intracellular signalling and thyroid hormone metabolism. Sec incorporation into selenoproteins employs a unique mechanism that involves decoding of the UGA stop codon. The process requires interplay between distinct, intrinsic features such as the Sec Insertion Sequence (SECIS) element, the tRNASec and multiple protein factors. The work presented in this thesis has focused on characterising the regulation of human SECIS binding protein 2, SBP2, a factor central to this process. Experimental approaches combined with bioinformatics analysis revealed that SBP2 is subjected to alternative splicing. A total of nine alternatively spliced transcripts appear to be expressed in cells, potentially encoding five different protein isoforms. The alternative splicing events are restricted to the 5?-region, which is proposed to be dispensable for Sec incorporation. One of the variants identified, contains a mitochondrial targeting sequence that was capable of targetting SBP2 into the mitochondrial compartment. This isoform also appears to be expressed endogenously within the mitochondria in cells. Previous reports have depicted SBP2 as a ribosomal protein, despite the presence of a putative Nuclear Localisation Signal (NLS). In this study it was found that SBP2 subcellular localisation is not restricted to ribosomes. Intrinsic functional NLS and Nuclear Export Signals (NESs), enable SBP2 to shuttle between the nucleus and the cytoplasm via the CRM1 pathway. In addition, the subcellular localisation of SBP2 appears to play an important role in regulating Sec incorporation into selenoproteins. The subcellular localisation of SBP2 is altered by conditions imposing oxidative stress. Several oxidising agents induce the nuclear accumulation of SBP2, which occurs via oxidation of cysteine residues within a novel redox-sensitive cysteine rich domain (CRD). Cysteine residues were to form disulfide bonds and glutathione-mixed disulfides during oxidising conditions, which are efficiently reversed in vitro by the thioredoxin and glutaredoxin systems, respectively. These modifications negatively regulate selenoprotein synthesis. Cells depleted of SBP2 are more sensitive to oxidative stress than control cells, which correlated with a substantial decrease in selenoprotein synthesis after treatment with oxidising agents. These results provide direct evidence that SBP2 is required for Sec incorporation in vivo and suggest that nuclear sequestration of SBP2 under such conditions may represent a mechanism to regulate the expression of selenoproteins. Collectively, these results suggest that SBP2 is regulated at multiple levels: by alternative splicing, changes in subcellar localisation and redox control.

<p>T lymphocytes are primarily involved in adaptive, cell-mediated, immune reactions. In this thesis T cells were studied regarding central and peripheral differentiation and homeostatic mechanisms for maintanance of the immune repertoire.</p><p>The influence by mature T cells on thymic development was studied in C.B-17 <i>scid/scid</i> (SCID) mice, devoid of mature T and B cells, and whose thymocyte development is arrested at the early pro-T cell stage. When mature syngeneic T cells were injected the developmental block was overcome and there was an accumulation of CD4⁺CD8⁺ thymocytes. This event was accompanied by the maturation of medullary epithelial cells in thymus which seemed to be driven by CD8⁺ T cells. In the periphery there was initially a spontaneous T-cell proliferation and later, the majority of the donor T lymphocytes showed a memory phenotype with high expression of CD44 and with an early onset of proliferation and cytokine production upon stimulation. This stable pool of memory type of cells sustained for more than a year following treatment.</p><p>Treating SCID mice with allogeneic T cells results in graft-versus-host disease (GVHD). Severe GVHD was dependent on the MHC-haplotype of the donor cells and was accompanied by profound alterations of the TCR-Vβ repertoire and with high production of IFN-γ.</p><p>Kappa light chain (κ)-deficient mice have only half the number of B cells as their normal counterparts but normal levels of immunoglobulins. When T cells from κ-deficient mice were stimulated <i>in vitro</i> there was a bias towards production of B-cell stimulatory type 2 cytokines. This is proposed as a mechanism for the homeostatic control of serum immunoglobulin levels in κ-deficient mice.</p>

Prader-Willi syndrome (PWS) is a rare, neurodevelopmental disorder with multiple features caused by hypothalamic deficiency, including infantile failure to thrive, hyperphagia leading to obesity, growth hormone deficiency, hypogonadism, and central adrenal insufficiency. Other features of PWS including global developmental delay, hypotonia, pain insensitivity, gastrointestinal dysfunction, and psychiatric disorders are caused by deficits in other regions of the nervous system. PWS is caused by the loss of a subset of paternally-expressed genes on chromosome 15, which includes NDN and MAGEL2. Necdin and Magel2 are both members of the melanoma antigen (MAGE) family of proteins and are expressed throughout development, particularly in the nervous system. This thesis describes experiments that examine the loss of function of necdin and Magel2 in mice and their potential roles in the pathogenesis of PWS. Targeted inactivation of Ndn and Magel2 in mice has aided in determining how loss of function of these proteins affects the development and function of the nervous system. Loss of necdin causes reduced axonal outgrowth and neuronal differentiation in the central and peripheral sensory nervous systems. I examined the autonomic nervous system in Ndn-null embryos and identified a defect in the migration of the most rostral sympathetic chain ganglion and consequently increased neuronal cell death and reduced innervation of target tissues supplied by this ganglion. Reduced axonal outgrowth was observed throughout the sympathetic nervous system in Ndn-null embryos although no gross deficits in the parasympathetic and enteric nervous systems were identified. Loss of Magel2 causes reduced fertility and abnormal circadian rhythm patterns in mice. I further identified an altered response to stress, a delayed response to insulin-induced hypoglycemia, a reduced stimulated growth hormone response, and lower thyroid hormone levels in Magel2-null mice, indicative of deficits in multiple hypothalamic-pituitary axes. The findings presented in this thesis support a role for necdin and Magel2 in the development and function of the nervous system. The data also indicates that these MAGE proteins play a key role in multiple features of PWS, including endocrine deficiencies and autonomic dysfunction

Der ubiquitär exprimierte, multifunktionale Glucosetransporter GLUT8 gehört zur Klasse III der Familie der passiven Glucosetransporter, die aus insgesamt 14 Proteinen besteht. Die fünf Mitglieder der Klasse IIII unterscheiden sich strukturell leicht von den Mitgliedern der Klasse I und II (Joost und Thorens, 2001). GLUT8 besitzt ein N-terminales Dileucin-Motiv, das Teil eines [DE]XXXL[LI] Motivs ist, welches für die Sortierung des Transporters in späte Endosomen und Lysosomen verantwortlich ist (Augustin et al., 2005). Da bis heute kein Signal identifiziert wurde, das eine Translokation des Transporters zur Plasmamembran auslöst, wird eine intrazelluläre Funktion von GLUT8 vermutet (Widmer et al., 2005). Im Rahmen der vorliegenden Arbeit wurde die intrazelluläre Funktion des Transporters in der Regulation der Glucosehomöostase des Körpers durch Analyse einer Slc2a8-knockout-Maus untersucht. Die homozygote Deletion des Transporters erbrachte lebensfähige Nachkommen, die sich augenscheinlich nicht von ihren Wildtyp-Geschwistern unterschieden. Allerdings wurde bei Verpaarungen heterozygoter Mäuse eine verminderte Anzahl an Slc2a8-/--Nachkommen beobachtet, die signifikant von der erwarteten Mendel’schen Verteilung abwich. Da Slc2a8 die höchste mRNA-Expression in den Testes aufwies und die Überprüfung der Fertilität mittels verschiedener homozygoter Verpaarungen eine Störung der weiblichen Fortpflanzungsfähigkeit ausschloss, wurden die Spermatozoen der Slc2a8-/--Mäuse eingehender untersucht. Als Ursache für die verringerte Anzahl von Slc2a8-/--Geburten wurde eine verminderte Prozentzahl motiler Slc2a8-/--Spermien ermittelt, die durch eine unzureichende mitochondriale Kondensation in den Spermien bedingt war. Diese Veränderung war mit einem reduzierten mitochondrialen Membranpotential assoziiert, was eine verminderte ATP-Produktion nach sich zog. Somit scheint GLUT8 in den Spermien an einem intrazellulären Transportprozess beteiligt zu sein, der einen Einfluss auf die oxidative Phosphorylierung der Mitochondrien ausübt. Im Gehirn wurde Slc2a8 besonders stark im Hippocampus exprimiert, der in der Regulation von körperlicher Aktivität, Explorationsverhalten, Erinnerungs- und Lernprozessen sowie Angst- und Stressreaktionen eine Rolle spielt. Außerdem wurde GLUT8 im Hypothalamus nachgewiesen, der unter anderem an der Regulation der Nahrungsaufnahme beteiligt ist. Die Slc2a8-/--Mäuse zeigten im Vergleich zu ihren Slc2a8+/+-Geschwistern eine signifikant gesteigerte körperliche Aktivität, die zusammen mit der von Membrez et al. (2006) publizierten erhöhten Zellproliferation im Hippocampus auf eine Nährstoffunterversorgung dieses Areals hindeutet. Die Nahrungsaufnahme war in Abwesenheit von GLUT8 nicht verändert, was zusammen mit dem nur geringfügig niedrigeren Körpergewicht der Slc2a8-/--Mäuse eine Funktion von GLUT8 im Glucose-sensing der Glucose-sensitiven Neurone des Gehirns ausschließt. Das leicht reduzierte Körpergewicht der Slc2a8-/--Mäuse ließ sich keinem bestimmten Organ- oder Gewebetyp zuordnen, sondern schien durch eine marginale Gewichtsreduktion aller untersuchten Gewebe bedingt zu sein. Zusammen mit den erniedrigten Blutglucosespiegeln und der anscheinend gesteigerten Lebenserwartung zeigten die Slc2a8-/--Mäuse Symptome einer leichten Nährstoffunterversorgung. GLUT8 scheint daher am Transport von Zuckerderivaten, die während des lysosomalen/endosomalen Abbaus von Glykoproteinen anfallen, beteiligt zu sein. Die so wiederaufbereiteten Zucker dienen dem Körper offenbar als zusätzliche Energiequelle. / The family of facilitative glucose transporters consists of 14 different members in human, which are divided into three classes (Joost and Thorens, 2001). The class III family member GLUT8 contains an amino-terminal dileucine sorting signal, which is part of the highly conserved [DE]XXXL[LI] motif responsible for the localization of GLUT8 in lysosomes and late endosomes (Augustin et al., 2005). To date there is no stimulus known, which translocates the transporter to the plasma membrane, therefore an intracellular function rather than at the cell surface is considered (Widmer et al., 2005). The aim of the present dissertation was to analyze the intracellular role of GLUT8 in the regulation of whole body glucose homeostasis, by the characterization of the corresponding knockout mice (Slc2a8-/-). Slc2a8-/- mice were viable and showed no obvious disparity to their wild-type littermates. However, analysis of the offspring distribution of heterozygous mating provided a reduced number of born Slc2a8-/- offspring which differed significantly from the expected Mendelian distribution. Because Slc2a8 mRNA is expressed at highest levels in the testis and the female Slc2a8-/- mice showed no alterations in fertility, we further investigated the function of Slc2a8-/- spermatozoa. An impaired mitochondrial condensation in the Slc2a8-/- spermatozoa, which was associated with decreased ATP levels resulted in a reduced number of motile Slc2a8-/- sperm, which appeared to be responsible for the reduced number of born Slc2a8-/- offspring. Therefore in sperm cells GLUT8 seems to be important for an intracellular transport process, which exerts an influence on the oxidative phosphorylation in the mitochondria. In the brain Slc2a8 is expressed at highest levels in the hippocampus, which is important for the regulation of physical activity, exploration behaviour, memory and learning as well as anxiety related behaviour. Additionally, GLUT8 was detected in the hypothalamus, which is amongst others involved in the regulation of food intake. The Slc2a8-/- mice showed a significant increase in locomotor activity, which indicates a moderate undersupply of the hippocampus area. According to this finding the group of Membrez et al. (2006) observed a raised cell proliferation in the hippocampus of Slc2a8-/- mice. The fact that no alterations in food intake and only a moderate reduction in body weight was detected in Slc2a8-/- mice, indicates that GLUT8 is not important for the hypothalamic glucose sensing. The marginal decreased body weight of the Slc2a8-/- mice appeared to be associated with a slightly reduced weight of different tissues. Together with the lowered blood glucose concentrations and the apparently enhanced lifespan, the Slc2a8-/- mice showed symptoms of a moderate undersupply compareable to caloric restriction. Thus, we hypothesize that GLUT8 is important for the transport of sugar derivatives which arise during lysosomal/endosomal degradation of glycoproteins. These recycled sugars may serve as an additional energy source in the cell.

Ghrelin is a unique hunger-inducing stomach-borne hormone. It activates orexigenic circuits in the central nervous system (CNS) when acylated with a fatty acid residue by the Ghrelin O-acyltransferase (GOAT). Soon after the discovery of ghrelin a theoretical model emerged which suggests that the gastric peptide ghrelin is the first “meal initiation molecule”. Ghrelin is also termed “hunger hormone” with a potentially important role as an endogenous regulator of energy balance. However, genetic deletion of ghrelin or its receptor, the growth hormone secretagogue receptor (GHSR), has only limited effects on appetite and obesity. Here we introduce novel mouse models of altered ghrelin, GHSR and GOAT function to reevaluate the role of the ghrelin system in regulating energy homeostasis. Simultaneous loss of ghrelin and GHSR function leads to decreased body weight and body fat, likely caused by increased energy expenditure and locomotor activity. Similarly, GOAT deficient mice are lighter and leaner than the wild-type controls. Mice overexpressing ghrelin and GOAT have increased body weight and fat mass along with decreased energy expenditure. Wild-type mouse studies show that fasting induces downregulation of the GOAT gene Mboat4 and decreases acyl ghrelin concentration in blood. We therefore hypothesized that GOAT rather depends on dietary than endogenous derived lipids for ghrelin acylation. Feeding studies show that GOAT uses the unnatural fatty acid heptanoate (C7) to acylate ghrelin, which clearly supports our theory. Further, acylation of overproduced ghrelin in our transgenic mouse model requires dietary supplementation of medium-chain-triglycerides, the preferred GOAT substrate. Our genetic models suggest that the ghrelin system plays an important physiological role in the control of energy metabolism. Thus, GOAT offers a novel peripheral drug target for the treatment of metabolic diseases. Moreover, our results suggest that ghrelin signaling may not be a result of absent nutrient intake, but indicate the availability of dietary lipids. We therefore propose that the ghrelin system functions as a novel lipid sensor, linking specific dietary lipids with the central-nervous control of energy metabolism. / Ghrelin ist ein einzigartiges im Magen produziertes Hormon, da es von dem Enzym Ghrelin O-acyltransferase (GOAT) mit einer mittelkettigen Fettsäure acyliert werden muss, um biologische Aktivität zu erlangen. Kurz nach seiner Entdeckung entstand die Hypothese, dass Ghrelin das „Hungerhormon“ sei und eine wichtige Rolle in der Regulation des Energiehaushalts spiele. Die genetische Manipulation von Ghrelin und seinem Rezeptor, dem GHSR, hat jedoch nur geringe Auswirkung auf Appetit und Körpergewicht. In der hier vorliegenden Studie stellen wir neuartige Mausmodelle mit abgewandelter Ghrelin-, GHSR- und GOATfunktion vor, um den Einfluss des Ghrelinsystems auf die Regulation der Energiehomöostase zu reevaluieren. Weiterhin wird die endogene Regulation von GOAT erstmalig beschrieben. Double-knockout Mäuse, die gleichzeitig defizitär für Ghrelin und GHSR sind, haben ein geringeres Körpergewicht, weniger Fettmasse und einen niedrigeren Energieverbrauch als Kontrolltiere. Knockout Mäuse für das GOAT Gen Mboat4 sind leichter und schlanker als Kontrolltiere. Dementsprechend haben transgene Mäuse, die Ghrelin und GOAT überproduzieren, eine erhöhte Fettmasse und einen verminderten Energieverbrauch. Weiterhin können wir zeigen, dass GOAT, anders als auf Grund der allgemein bekannten Ghrelinfunktion angenommen, nicht durch Hungern aktiviert wird. Bei Mäusen, die gefastet haben, ist die Genexpression von Mboat4 deutlich herunterreguliert, woraus ein geringer Blutspiegel von Acyl-Ghrelin resultiert. Daraus haben wir geschlossen, dass GOAT eventuell Nahrungsfette und nicht die durch Hungern freigesetzten endogen Fettsäuren zur Ghrelinacylierung benutzt. Fütterungsversuche bestätigen diese Hypothese, da GOAT die unnatürliche Fettsäure Heptan Säure (C7), die der Tiernahrung beigefügt wurde, zur Ghrelinacylierung verwendet. Ein weiteres Indiz für die Notwendigkeit von Nahrungsfetten für die Ghrelinacylierung ist, dass die transgenen Ghrelin/GOAT Mäuse nur massiv Acyl-Ghrelin produzieren, wenn sie mit einer Diät gefüttert werden, die mit mittelkettigen Fettsäuren angereichert ist. Zusammenfassend zeigt die Studie, dass das Ghrelinsystem maßgeblich an der Regulation der Energiehomöostase beteiligt ist und dass die Ghrelinaktivierung direkt von Nahrungsfetten beeinflusst wird. Daraus könnte geschlossen werden, dass Ghrelin wohlmöglich nicht das Hungerhormon ist, wie bisher generell angenommen wurde. Ghrelin könnte vielmehr ein potentieller “Fettsensor” sein, der dem Gehirn die Verfügbarkeit von fettreicher Nahrung signalisiert und somit den Metabolismus zur optimalen Verwertung und Speicherung der aufgenommenen Energie beeinflusst.

The plasma membrane of eukaryotic cells contains cholesterol and glycosphingolipids enriched nanodomains known as lipid rafts; which are believed to exist in a liquid ordered (lo) state. Methyl-beta-cyclodextrin (MBCD) is used to deplete cellular cholesterol and a widespread assumption is that MBCD preferentially targets cholesterol in lipid rafts. To analyze this in T cells a progressive cholesterol extraction protocols was established. At 37ºC, MBCD treatment does not lead to the preferential loss of cholesterol from TX-DRMs. At 0ºC only 35% of total cholesterol could be extracted demonstrating that less than 35% of the cell’s cholesterol is found in the plasma membrane. Moreover, incubation of cells at 0ºC causes loss of plasma membrane cholesterol and an increase in cholesteryl esters. The increase in cholesterol esters upon cold exposure is linked to the cholesterol concentration induced activation of ACAT enzyme which converts cholesterol to cholesteryl esters. Cholesterol concentration specific activation of ACAT and conversion of cholesterol to cholesteryl esters during the loading of cholesterol onto T cells by MBCD was also observed. By using MBCD for progressive cholesterol depletion from T cells at 37ºC, the effect of cholesterol depletion on T cell signaling was addressed. At 10-20% cholesterol depletion levels, tyrosine phosphorylation is increased and ERK is activated. Peripheral actin polymerization, cell spreading and membrane protrusions are also triggered by limited cholesterol depletion. Upon limited cholesterol depletion aggregation of lipid rafts in the plasma membrane was observed. The aggregation of lipid rafts upon cholesterol depletion does not dependent on the signaling proteins such as Src-kinases. Upon cholesterol depletion there is an increase in overall plasma membrane order, indicative of more ordered domains forming at the expense of disordered domains. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: In press.</p>

T lymphocytes are primarily involved in adaptive, cell-mediated, immune reactions. In this thesis T cells were studied regarding central and peripheral differentiation and homeostatic mechanisms for maintanance of the immune repertoire. The influence by mature T cells on thymic development was studied in C.B-17 scid/scid (SCID) mice, devoid of mature T and B cells, and whose thymocyte development is arrested at the early pro-T cell stage. When mature syngeneic T cells were injected the developmental block was overcome and there was an accumulation of CD4+CD8+ thymocytes. This event was accompanied by the maturation of medullary epithelial cells in thymus which seemed to be driven by CD8+ T cells. In the periphery there was initially a spontaneous T-cell proliferation and later, the majority of the donor T lymphocytes showed a memory phenotype with high expression of CD44 and with an early onset of proliferation and cytokine production upon stimulation. This stable pool of memory type of cells sustained for more than a year following treatment. Treating SCID mice with allogeneic T cells results in graft-versus-host disease (GVHD). Severe GVHD was dependent on the MHC-haplotype of the donor cells and was accompanied by profound alterations of the TCR-Vβ repertoire and with high production of IFN-γ. Kappa light chain (κ)-deficient mice have only half the number of B cells as their normal counterparts but normal levels of immunoglobulins. When T cells from κ-deficient mice were stimulated in vitro there was a bias towards production of B-cell stimulatory type 2 cytokines. This is proposed as a mechanism for the homeostatic control of serum immunoglobulin levels in κ-deficient mice.