Rejuvenation of the aging thymus: growth hormone-mediated and ghrelin-mediated signaling pathways

Effect of acute and regular exercise on growth hormone secretagogue receptor-1a expression in human lymphocytes, T cell subpopulation and monocytes

The orexigenic peptide hormone ghrelin exerts potent inhibitory effects on pro-inflammatory cytokine release via the growth hormone secretagogue receptor-1a (GHS-R1a) on T cells and monocytes. As such, ghrelin is a promising therapeutic agent for the treatment of inflammatory conditions, but these effects depend on the availability of GHS-R1a. The aim of this study was to determine the effect of acute exercise on GHS-R1a expression on circulating CD14+ monocytes, total lymphocytes and CD3+ T cells. Nine male club-standard cyclists cycled for 1h at 75% V̇O2peak (EX) or rested (REST) in a randomised cross-over design. Compared with the equivalent times in REST, the concentration of circulating GHS-R1a+ lymphocytes and monocytes was higher in EX at immediately and 1 and 2h post-exercise (all p<.05). The concentration of CD3+GHS-R1a+ cells was higher in EX than in REST immediately post-exercise only (258 (203)cellsμl(-1) vs. 62 (42)cellsμl(-1), p<.05). Density of GHS-R1a receptor expression was unaffected by trial or time. Comparison of active participants at rest with 7 age-, sex- and BMI-matched sedentary controls revealed a higher concentration of GHS-R1a+ lymphocytes in active males (p<.05). These findings suggest a preferential recruitment of specific cell subpopulations expressing GHS-R1a into the peripheral circulation with acute and regular exercise. Given that the anti-inflammatory effects of ghrelin depend on the availability of GHS-R1a, the preferential recruitment of subpopulations with high anti-inflammatory potential found here add a novel aspect to the potential mechanisms by which exercise acts to reduce pro-inflammatory cytokine levels.

Serum ghrelin and adiponectin levels are increased but serum leptin level is unchanged in low weight Chronic Obstructive Pulmonary Disease patients

BACKGROUND

Weight loss and muscle wasting are common features reported in COPD patients and they are all related with systemic inflammation. In this study, the relationship between pulmonary functions and inflammatory and metabolic parameters in low weight COPD patients were investigated.

METHODS

Fifty male COPD patients were grouped according to the Global Initiative for Chronic Obstructive Lung Disease criteria. Group 1: Mild-moderate COPD patients (n=18; with a mean age of 66.4 ± 9.2 yrs; body mass index (BMI):19.7 ± 1.5 kg/m(2)), group 2: Severe-very severe COPD patients (n=32; with a mean age of 65.9 ± 10.0 yrs; BMI:19.3 ± 1.6 kg/m(2)), group 3: Control group composed of healthy nonsmoking males (n=17; with a mean age of 50.2 ± 8.4 yrs; BMI:21.85 ± 1.5 kg/m(2)). Anthropometric parameters, serum levels of adiponectin (ApN), ghrelin, leptin, hsCRP, IL-6, IL-1β, IL-8, TNF-α and pulmonary functions were compared.

RESULTS

Adiponectin concentration was higher in group 1 (43.3 ± 28.6 ng/mL; p<0.05) and group 2 (59.9 ± 31.8 ng/mL; p<0.001) when compared with the control group (23.5 ± 13.6 ng/mL). Ghrelin concentrations were higher in COPD groups (1281.0 ± 1173.7 and 1840.0 ± 403.6 pg/mL; p<0.05) compared to the control subjects (554.0 ± 281.9 pg/mL). When the groups were compared, no significant difference was found for leptin, IL-1β, TNF-α, and IL-8. Interleukin-6 and hsCRP levels were higher in group 1 than in the control group. ApN was negatively correlated with BMI and FEV1. In all groups, FEV1 showed positive correlation with BMI, skinfold thicknesses, insulin and triglyceride; negative correlation with age, pack/years, HDL-Chol and ApN. Increased SHBG with decreased insulin level and HOMA-IR may indicate increased insulin sensitivity in COPD groups.

CONCLUSION

The anti-inflammatory effect of ApN and ghrelin is more evident in severe-very severe COPD patients.

WNT signaling suppression in the senescent human thymus

Human thymus is completely developed in late fetal stages and its function peaks in newborns. After the first year of life, the thymus undergoes a progressive atrophy that dramatically decreases de novo T-lymphocyte maturation. Hormonal signaling and changes in the microRNA expression network are identified as underlying causes of human thymus involution. However, specific pathways involved in the age-related loss of thymic function remain unknown. In this study, we analyzed differential gene-expression profile and microRNA expression in elderly (70 years old) and young (less than 10 months old and 11 years old) human thymic samples. Our data have shown that WNT pathway deregulation through the overexpression of different inhibitors by the nonadipocytic component of the human thymus stimulates the age-related involution. These results are of particular interest because interference of WNT signaling has been demonstrated in both animal models and in vitro studies, with the three major hallmarks of thymic involution: (i) epithelial structure disruption, (ii) adipogenic process, and (iii) thymocyte development arrest. Thus, our results suggest that secreted inhibitors of the WNT pathway could be explored as a novel therapeutical target in the reversal of the age-related thymic involution.

Thymus and aging: morphological, radiological, and functional overview

Aging is a continuous process that induces many alterations in the cytoarchitecture of different organs and systems both in humans and animals. Moreover, it is associated with increased susceptibility to infectious, autoimmune, and neoplastic processes. The thymus is a primary lymphoid organ responsible for the production of immunocompetent T cells and, with aging, it atrophies and declines in functions. Universality of thymic involution in all species possessing thymus, including human, indicates it as a long-standing evolutionary event. Although it is accepted that many factors contribute to age-associated thymic involution, little is known about the mechanisms involved in the process. The exact time point of the initiation is not well defined. To address the issue, we report the exact age of thymus throughout the review so that readers can have a nicely pictured synoptic view of the process. Focusing our attention on the different stages of the development of the thymus gland (natal, postnatal, adult, and old), we describe chronologically the morphological changes of the gland. We report that the thymic morphology and cell types are evolutionarily preserved in several vertebrate species. This finding is important in understanding the similar problems caused by senescence and other diseases. Another point that we considered very important is to indicate the assessment of the thymus through radiological images to highlight its variability in shape, size, and anatomical conformation.

IBD across the age spectrum: is it the same disease?

IBD is a chronic disorder with disease onset ranging from early childhood to beyond the sixth decade of life. The factors that determine the age of onset currently remain unexplained. Is timing of occurrence a random event or is it indicative of different pathophysiological pathways leading to different phenotypes across the age spectrum? Over the past decade, several studies have suggested that the characteristics and natural history of IBD seem to be different according to age of onset. This heterogeneity suggests that the respective contributions of genetics, host immune system and environment to the aetiology and phenotype of Crohn's disease and ulcerative colitis are different across ages. Critical reviews that focus on differences characterizing IBD between age groups are scarce. Therefore, this Review updates the knowledge of the differences in epidemiology, clinical characteristics, and natural history of paediatric, adult and elderly-onset IBD. In addition, potential differences in host-gene-microbial interactions according to age are highlighted.

Ghrelin gene products, receptors, and GOAT enzyme: biological and pathophysiological insight

Ghrelin is a 28-amino acid acylated hormone, highly expressed in the stomach, which binds to its cognate receptor (GHSR1a) to regulate a plethora of relevant biological processes, including food intake, energy balance, hormonal secretions, learning, inflammation, etc. However, ghrelin is, in fact, the most notorious component of a complex, intricate regulatory system comprised of a growing number of alternative peptides (e.g. obestatin, unacylated ghrelin, and In1-ghrelin, etc.), known (GHSRs) and, necessarily unknown receptors, as well as modifying enzymes (e.g. ghrelin-O-acyl-transferase), which interact among them as well as with other regulatory systems in order to tightly modulate key (patho)-physiological processes. This multiplicity of functions and versatility of the ghrelin system arise from a dual, genetic and functional, complexity. Importantly, a growing body of evidence suggests that dysregulation in some of the components of the ghrelin system can lead to or influence the development and/or progression of highly concerning pathologies such as endocrine-related tumors, inflammatory/cardiovascular diseases, and neurodegeneration, wherein these altered components could be used as diagnostic, prognostic, or therapeutic targets. In this context, the aim of this review is to integrate and comprehensively analyze the multiple components and functions of the ghrelin system described to date in order to define and understand its biological and (patho)-physiological significance.

Clinical strategies to enhance thymic recovery after allogeneic hematopoietic stem cell transplantation

The thymus is particularly sensitive to injury caused by cytoreductive chemo- or radiation therapy, shock, infection and graft versus host disease. Insufficient thymic recovery has been directly correlated with increased risk of opportunistic infections and poor clinical outcomes in recipients of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Prolonged immune deficiency is particularly pronounced in older patients whose thymi are already significantly impaired due to age-related thymic involution. Preclinical and clinical studies have revealed several strategies that can enhance thymic function and immune reconstitution after transplant, including sex steroid ablation, growth factors (growth hormone, keratinocyte growth factor, insulin-like growth factor 1, interleukin-7) and ex vivo generated precursor T cells. In addition, recent studies have shown that other approaches, such as interleukein-22 and nutritional changes, may represent additional candidates to enhance thymic regeneration. In this review we provide updates on these strategies and comment on their potential to be translated into clinical therapies.

Thymic rejuvenation and aging

The thymus is a vital organ for homeostatic maintenance of the peripheral immune system. It is within this mediastinal tissue that T cells develop and are extensively educated and exported to the periphery for establishment of a functional and effective immune system. A striking paradoxical feature of this critical lymphoid tissue is that it undergoes profound age-associated involution. Thymic decline is of minimal consequence to healthy individuals, but the reduced efficacy of the immune system with age has direct etiological linkages with an increase in diseases including opportunistic infections, autoimmunity, and incidence/burden of cancer. Furthermore the inability of adults to restore immune function following insult induced by chemotherapy, ionizing radiation exposure or therapy, and infections (e.g. HIV-1) leads to increased morbidity and often mortality in the elderly. For these reasons, it is important that investigators strive to translate their understanding of mechanisms that drive thymic involution, and develop safe and effective strategies to rejuvenate the thymus in settings of clinical need. In this review, we present a discussion of the current status of thymic rejuvenation efforts associated with: sex steroid ablation, cytokines, growth factors, and hormones.

The mitochondria-targeted antioxidant SkQ1 but not N-acetylcysteine reverses aging-related biomarkers in rats

Although antioxidants have been repeatedly tested in animal models and clinical studies, there is no evidence that antioxidants reduce already developed age-related decline. Recently we demonstrated that mitochondria-targeted antioxidant 10-(6'-plastoquinonyl) decyltriphenylphosphonium (SkQ1) delayed some manifestations of aging. Here we compared effects of SkQ1 and N-acetyl-L-cysteine (NAC) on age-dependent decline in blood levels of leukocytes, growth hormone (GH), insulin-like growth factor-1 (IGF-1), testosterone, dehydroepiandrosterone (DHEA) in Wistar and senescence-accelerated OXYS rats. When started late in life, supplementation with SkQ1 not only prevented age-related decline but also significantly reversed it. With NAC, all the observed effects were of the lower magnitude compared with SkQ1 (in spite of that dose of NAC was 16000 times higher). We suggest that supplementation with low doses of SkQ1 is a promising intervention to achieve a healthy ageing.

Plasma ghrelin and pro-inflammatory markers in patients with obstructive sleep apnea and stable coronary heart disease

Background

Inflammation is associated with obstructive sleep apnea (OSA) and coronary heart disease (CHD). Ghrelin, a multifunctional hormone, may play a key role in patients with OSA and/or CHD. The aim of this study was to investigate plasma ghrelin and pro-inflammatory cytokines in patients with OSA and/or CHD and assess the association of these cytokines with ghrelin.

Material/Methods

Plasma ghrelin, interleukin-6(IL-6) and tumor necrosis factor alpha (TNF-α) were measured in 75 patients and in 25 age-, sex-, and BMI-matched healthy control subjects. These patients were further classified into 3 groups (25 with OSA, 25 with OSA and CHD, and 25 with CHD), matched for age, sex, body mass index, and the severity of OSA or CHD.

Results

Plasma ghrelin levels were increased, and TNF-α and IL-6 were decreased in OSA patients with and without CHD, when compared with controls with similar CHD clinical characteristics (both P<0.05). Further, OSA patients with CHD tended to have higher plasma levels of TNF-α and IL-6, and lower plasma levels of ghrelin than OSA controls (P>0.05). Notably, plasma ghrelin levels were independently negatively correlated with plasma TNF-α and IL-6 (P<0.05).

Conclusions

Increased plasma ghrelin levels might constitute an independent determinant of decreased TNF-α and IL-6, suggesting that higher ghrelin level may in part represent a compensatory mechanism to overcome the pro-inflammatory effects of OSA. Further large-scale and prospective studies are needed to confirm these effects.

Ghrelin-leptin network influences serum chitinase 3-like protein 1 (YKL-40) levels in obese prepubertal children

OBJECTIVE

This study aimed to investigate any possible interactions between hormonal regulators of weight gain and markers of subclinical inflammation in childhood obesity. Forty-one obese prepubertal children and 41 age- and gender-matched lean controls were included. Children were classified as obese or non-obese according to international age- and gender-specific body mass index (BMI) cutoff points defined by the International Obesity Task Force to define childhood obesity. Anthropometric measurements, serum insulin, chitinase 3-like protein (YKL-40), ghrelin and leptin levels as well as plasma glucose in the fasting state were determined.

RESULTS

Obese children as compared with controls had higher YKL-40 (50.7±15.2 vs 41.0±10.5 ng/ml, p=0.003), higher leptin (33.8±16.0 vs 9.7±7.5 ng/ml, p<0.001) and lower ghrelin serum levels (871.4±368.0 vs 1417.6±387.3 pg/ml, p<0.001). The obese children with ghrelin levels above median (43.8±10.2 ng/ml) as compared to those with ghrelin below median (57.2±16.6 ng/ml) presented lower serum YKL-40 levels (p=0.009), indicating more severe inflammation with lower levels of ghrelin. By contrast, although the obese children with leptin levels above median (49.7±16.3 ng/ml) presented lower serum YKL-40 levels as compared to those with leptin levels below median (51.6±14.6 ng/ml), this difference did not reach the level of statistical significance (p=0.726). Moreover, serum YKL-40 levels were significantly correlated with ghrelin (r=-0.359, p=0.014) but not with leptin levels (r=0.169, p=0.261). A significant negative correlation between ghrelin and leptin levels was also found (r=-0.276, p=0.041). These findings remained unchanged for obese, when analyses were done separately, whereas the significance of correlations was lost for non-obese subjects.

CONCLUSIONS

Ghrelin-leptin network had an impact on serum YKL-40 levels in obese prepubertal children; upregulation of YKL-40 secretion seems to be a consequence of reduced ghrelin rather than elevated leptin concentrations.

Causes, consequences, and reversal of immune system aging

The effects of aging on the immune system are manifest at multiple levels that include reduced production of B and T cells in bone marrow and thymus and diminished function of mature lymphocytes in secondary lymphoid tissues. As a result, elderly individuals do not respond to immune challenge as robustly as the young. An important goal of aging research is to define the cellular changes that occur in the immune system and the molecular events that underlie them. Considerable progress has been made in this regard, and this information has provided the rationale for clinical trials to rejuvenate the aging immune system.

Growth hormone modulates migration of thymocytes and peripheral T cells

In the context of immunoneuroendocrine cross talk, growth hormone (GH) exerts pleiotropic effects in the immune system. For example, GH-transgenic mice, as well as animals and humans treated with GH, exhibit enhanced cellularity in the thymus. GH also stimulates the thymic microenvironment, augmenting chemokine and extracellular matrix (ECM) production, with consequent increase in ECM- and chemokine-driven thymocyte migratory responses. Peripheral T cell migration triggered by laminin or fibronectin was enhanced in cells from GH-transgenic versus wild-type control adult mice, as seen for CD4(+) and CD8(+) T cells from mesenteric lymph nodes. Migration of these T lymphocytes, triggered by the chemokine CXCL12, in conjunction with laminin or fibronectin, was also enhanced compared with control counterparts. Considering that GH can be used as an adjuvant therapy in immunodeficiencies, including AIDS, the concepts defined herein, that GH enhances developing and peripheral T cell migration, provide new clues for future GH-related immune interventions.

Presentation of neuroendocrine self in the thymus: a necessity for integrated evolution of the immune and neuroendocrine systems

During evolution, from ancestor thymoids scattered in gill baskets of the lamprey, the first unique thymus appeared in jawed cartilaginous fishes around 450-500 millions years ago, concomitantly or shortly after the emergence of recombinase-dependent adaptive immunity. The major biological function of the thymus is to generate a diverse repertoire of T cell receptors that are self tolerant. The thymus achieves this role by using two complementary and intimately associated mechanisms: apoptotic deletion of T cell clones bearing a TCR with high affinity for self-antigens presented by MHC proteins on thymic epithelial cells (TECs) and dendritic cells (DCs); and generation of self-antigen-specific natural regulatory T (nT(reg)) cells. Moreover, the escape from thymic central self-tolerance plays a primary role in the development of autoimmune diseases that are a significant burden for the quality of life and health-care cost. Our new knowledge in thymus physiology and physiopathology is currently translated into innovative therapeutic strategies against these devastating chronic diseases.

Thymus Size and Age-related Thymic Involution: Early Programming, Sexual Dimorphism, Progenitors and Stroma

Age-related thymic involution is characterized by a progressive regression in thymus size and a diminishment of thymic structure. A decrease in thymic compartments leads to the reduction of thymopoiesis. Thymic involution is closely associated with immunosenescence, a degeneration of the immune system primarily due to the alterations in T-cell composition. Strategies to improve the consequences of the aging thymus are currently under investigation. A wide array of knowledge has revealed a series of factors that are essential in the overall determination of thymic function and immune response. Evidence indicates that early programming of the thymus, sexual dimorphism, and the efficiency of specific T-cell progenitors and the thymic microenvironment are all crucial determinants of immune activity from early life through advanced ages. To fully understand the processes involved in age-related thymic involution, such determinants must be considered. The central purpose of this review is to emphasize previous and most recent evidence suggesting that these factors contribute to the influence of long-term immunity and ultimately shape the progression of thymic involution in advanced age.

Genetic regulation of thymocyte progenitor aging

The number of T cell progenitors is significantly reduced in the involuted thymus, and the growth and developmental potential of the few cells that are present is severely attenuated. This review provides an overview of how aging affects T cell precursors before and following entry into the thymus and discusses the age-related genetic changes that may occur in them. Finally, interventions that rejuvenate thymopoiesis in the elderly by targeting T cell progenitors are discussed.

Regenerative capacity of adult cortical thymic epithelial cells

Involution of the thymus is accompanied by a decline in the number of thymic epithelial cells (TECs) and a severely restricted peripheral repertoire of T-cell specificities. TECs are essential for T-cell differentiation; they originate from a bipotent progenitor that gives rise to cells of cortical (cTEC) and medullary (mTEC) phenotypes, via compartment-specific progenitors. Upon acute selective near-total ablation during embryogenesis, regeneration of TECs fails, suggesting that losses from the pool of TEC progenitors are not compensated. However, it is unclear whether this is also true for the compartment-specific progenitors. The decline of cTECs is a prominent feature of thymic involution. Because cTECs support early stages of T-cell development and hence determine the overall lymphopoietic capacity of the thymus, it is possible that the lack of sustained regenerative capacity of cTEC progenitor cells underlies the process of thymic involution. Here, we examine this hypothesis by cell-type-specific conditional ablation of cTECs. Expression of the human diphtheria toxin receptor (hDTR) gene under the regulatory influence of the chemokine receptor Ccx-ckr1 gene renders cTECs sensitive to the cytotoxic effects of diphtheria toxin (DT). As expected, DT treatment of preadolescent and adult mice led to a dramatic loss of cTECs, accompanied by a rapid demise of immature thymocytes. Unexpectedly, however, the cTEC compartment regenerated after cessation of treatment, accompanied by the restoration of T-cell development. These findings provide the basis for the development of targeted interventions unlocking the latent regenerative potential of cTECs to counter thymic involution.

Towards segmentation of the thymus in fat and water parametric MR images

The thymus, an organ responsible for the development, selection, and maintenance of the peripheral T-cell population, is an important regulator of the immune system. Despite its physiological significance, it has received little attention in the medical image analysis literature. In practice, the anatomical location and variable shape of this gland pose challenges both in the image acquisition and analysis processes. We present an automated method for segmenting the thymus from water and fat parametric MR images that permits further analysis of volumetrics and tissue characterization. We compute fat ratio and water ratio parametric images and introduce the use of a stochastic edge detector that is embedded in a geometric variational segmentation model. Validation experiments of the proposed algorithm against manual delineations of the thymus indicate the applicability of our approach.

Mechanisms of immunosenescence: lessons from models of accelerated immune aging

With increasing age, the ability of the adaptive immune system to respond to vaccines and to protect from infection declines. In parallel, the production of inflammatory mediators increases. While cross-sectional studies have been successful in defining age-dependent immunological phenotypes, studies of accelerated immune aging in human subpopulations have been instrumental in obtaining mechanistic insights. The immune system depends on its regenerative capacity; however, the T cell repertoire, once established, is relatively robust to aging and only decompensates when additionally stressed. Such stressors include chronic infections such as CMV and HIV, even when viral replication is controlled, and autoimmune diseases. Reduced regenerative capacity, chronic immune activation in the absence of cell exhaustion, T cell memory inflation, and accumulation of highly potent effector T cells in these patients synergize to develop an immune phenotype that is characteristic of the elderly. Studies of accelerated immune aging in autoimmune diseases have identified an unexpected link to chronic DNA damage responses that are known to be important in aging, but so far had not been implicated in immune aging.

Gene polymorphisms: the keys for marker assisted selection and unraveling core regulatory pathways for mastitis resistance

One of the most frequent mammary diseases impacting lactating animals is mastitis, an inflammation of the mammary gland most commonly caused by bacterial infection. The severity of mastitis is greatly influenced by the invading organism and the subsequent immune response which must recognize the foreign organism, recruit immune cells, eliminate the invading pathogen, and resolve the inflammatory response. The speed, strength, and duration of this response and subsequent disease susceptibility are critically tied to the genetic background of an animal. However, the genetic contribution has been difficult to identify due to the complex interactions that must occur for effective disease resistance. Recent studies have utilized polymorphisms to better define the genes and chromosomal regions that contribute to mastitis resistance. This review will examine these studies with primary emphasis in bovine systems, as the most work regarding mastitis has been conducted in this species.

Identification of ghrelin receptor blocker, D-[Lys3] GHRP-6 as a CXCR4 receptor antagonist

[D-Lys3]-Growth Hormone Releasing Peptide-6 (DLS) is widely utilized in vivo and in vitro as a selective ghrelin receptor (GHS-R) antagonist. Unexpectedly, we identified that DLS also has the ability to block CXCL12 binding and activity through CXCR4 on T cells and peripheral blood mononuclear cells (PBMCs). Moreover, as CXCR4 has been shown to act as a major co-receptor for HIV-1 entry into CD4 positive host cells, we have also found that DLS partially blocks CXCR4-mediated HIV-1 entry and propagation in activated human PBMCs. These data demonstrate that DLS is not the specific and selective antagonist as thought for GHS-R1a and appears to have additional effects on the CXCR4 chemokine receptor. Our findings also suggest that structural analogues that mimic DLS binding properties may also have properties of blocking HIV infectivity, CXCR4 dependent cancer cell migration and attenuating chemokine-mediated immune cell trafficking in inflammatory disorders.

Ghrelin-mediated appetite regulation in the central nervous system

The gut hormone and neuropeptide ghrelin was initially identified in the periphery as a compound released in the bloodstream in response to a negative energetic status. In the central nervous system (CNS), ghrelin mainly acts on the hypothalamus and the limbic system, with its best-known biological role being the regulation of appetitive functions. Recent research has shown that ghrelin is not an indispensable factor in the regulation of food intake. However, it plays a key role in the metabolic changes of lipids, mainly those involving hypothalamic NOS, AMPK, CaMKK2, CPT1 and UCP2 proteins. Ghrelin participates in the regulation of memory processes and the feeling of pleasure resulting from eating, both of which are metabolism-dependent and may be essential for the successful achievement of adaptive appetitive behavior. Ghrelin exerts its biological effect through a complicated network of neuroendocrine links, including the melanocortin and endocannabinoid systems. The activity of ghrelin is connected with circadian and annual fluctuations, which depend on seasons and food availability.

Elderly at greater risk for root caries: a look at the multifactorial risks with emphasis on genetics susceptibility

Root caries is one of the most significant dental problems among older adults today. Many studies have demonstrated that older adults are at greater risk for developing root caries. Here we examine what risk factors older adults are prone to and explain how they contribute to higher rates of oral disease, in particular root caries. The elderly are at risk for root caries due to dentures, lack of dexterity, a shift from complex to simple sugars, and poor oral hygiene. Decreased salivary flow and its manifestations with other social/behavioral and medical factors may provide a more comprehensive explanation to a higher frequency of root caries in older adults.

The effects of ghrelin on inflammation and the immune system

A number of hormones and metabolic mediators signal the brain of changes in the body's energy status and when an imbalance occurs; the brain coordinates the appropriate changes in energy intake and utilization via the control of appetite and food consumption. Under conditions of chronic inflammation and immune activation, there is often a significant loss of body mass and appetite suggesting the presence of shared ligands and signaling pathways mediating "crosstalk" between the immune and neuroendocrine systems. Ghrelin, the endogenous ligand for growth hormone secretagogue receptor (GHS-R), is produced primarily by cells in the stomach and serves as a potent circulating orexigenic hormone controlling food intake, energy expenditure, adiposity and GH secretion. The functional roles of ghrelin and other growth hormone secretagogues (GHS) within the immune system and under states of inflammatory stress and injury are only now coming to light. A number of reports over the past decade have described ghrelin to be a potent anti-inflammatory mediator both in vitro and in vivo and a promising therapeutic agent in the treatment of inflammatory diseases and injury. Moreover, ghrelin has also been shown to promote lymphocyte development in the primary lymphoid organs (bone marrow and thymus) and to ablate age-associated thymic involution. In the current report, we review the literature supporting a role for ghrelin as an anti-inflammatory agent and immunoregulatory hormone/cytokine and its potential use in the treatment of inflammatory diseases and injury.

Thymic T-cell development in allogeneic stem cell transplantation

Cytoreductive conditioning regimens used in the context of allogeneic hematopoietic cell transplantation (HCT) elicit deficits in innate and adaptive immunity, which predispose patients to infections. As such, transplantation outcomes depend vitally on the successful reconstruction of immune competence. Restoration of a normal peripheral T-cell pool after HCT is a slow process that requires the de novo production of naive T cells in a functionally competent thymus. However, there are several challenges to this regenerative process. Most notably, advanced age, the cytotoxic pretransplantation conditioning, and posttransplantation alloreactivity are risk factors for T-cell immune deficiency as they independently interfere with normal thymus function. Here, we discuss preclinical allogeneic HCT models and clinical observations that have contributed to a better understanding of the transplant-related thymic dysfunction. The identification of the cellular and molecular mechanisms that control regular thymopoiesis but are altered in HCT patients is expected to provide the basis for new therapies that improve the regeneration of the adaptive immune system, especially with functionally competent, naive T cells.

Positioning effects of KillerRed inside of cells correlate with DNA strand breaks after activation with visible light

Fluorescent proteins (FPs) are established tools for new applications, not-restricted to the cell biological research. They could also be ideal in surgery enhancing the precision to differentiate between the target tissue and the surrounding healthy tissue. FPs like the KillerRed (KRED), used here, can be activated by excitation with visible day-light for emitting active electrons which produce reactive oxygen species (ROS) resulting in photokilling processes. It is a given that the extent of the KRED's cell toxicity depends on its subcellular localization. Evidences are documented that the nuclear lamina as well as especially the chromatin are critical targets for KRED-mediated ROS-based DNA damaging. Here we investigated the damaging effects of the KRED protein fused to the nuclear lamina and to the histone H2A DNA-binding protein. We detected a frequency of DNA strand breaks, dependent first on the illumination time, and second on the spatial distance between the localization at the chromatin and the site of ROS production. As a consequence we could identify defined DNA bands with 200, 400 and (600) bps as most prominent degradation products, presumably representing an internucleosomal DNA cleavage induced by KRED. These findings are not restricted to the detection of programmed cell death processes in the therapeutic field like PDT, but they can also contribute to a better understanding of the structure-function relations in the epigenomic world.

The role of the thymus in the integrated evolution of the recombinase-dependent adaptive immune response and the neuroendocrine system

Before being able to react against infectious non-self-antigens, the immune system has to be educated in recognition and tolerance of neuroendocrine self-proteins. This sophisticated educational process takes place only in the thymus. The development of an autoimmune response directed to neuroendocrine glands has been shown to result from a thymus dysfunction in programming immunological self-tolerance to neuroendocrine-related antigens. This thymus dysfunction leads to a breakdown of immune homeostasis with an enrichment of 'forbidden' self-reactive T cells and a deficiency in self-antigen-specific natural regulatory T cells in the peripheral T lymphocyte repertoire. A large number of neuroendocrine self-antigens are expressed by the thymic epithelium, under the control of the autoimmune regulator (AIRE) gene/protein in the medulla. Based on the close homology and cross-tolerance between thymic type 1 diabetes-related self-antigens and peripheral antigens targeted in β-cells by autoimmunity, a novel type of vaccination is currently developed for the prevention and cure of type 1 diabetes. If this approach were found to be effective in reprogramming immunological tolerance that is absent or broken in this disease, it could pave the way for the design of negative/tolerogenic self-vaccines against other endocrine and organ-specific autoimmune disorders.