Thymic rejuvenation and aging

Endocrine disrupters affect the immune system of fish: The example of the European seabass

An organism's fitness critically relies on its immune system to provide protection against parasites and pathogens. The immune system has reached its highest complexity in vertebrates, combining the highly specific adaptive with the non-specific innate immunity. In vertebrates, a complex system of steroid hormones regulates major physiological functions comprising energy metabolism, growth, reproduction and immune system performance. This allows the organism to allocate available energy according to life-history traits and environmental conditions, thus maintaining homeostasis and survival of the individual and of the population. Immune system activation must take into account the developmental stage and the nutritional state of the organism. It should respond adequately to different pathogens, but should not overperform or consume all resources for other physiological functions. This important trade-off between immunity and reproduction is balanced by oestrogen. Many of the thousands of chemicals released by humans into the environment, so-called xenobiotics, have the ability to disrupt normal endocrine function. Such endocrine-disrupting chemicals have been demonstrated to impair reproductive functions and to be responsible for numerous diseases in humans and wild life. Given that oestrogens are established modulators of immune cell populations, exogenous oestrogens and oestrogen mimics can modulate immune functions in aquatic animals, such as fish, potentially affecting wildlife and aquaculture. This review highlights the interaction of xenoestrogens with fish immunity. It particularly focusses on the thymus, a major primary immune organ, in the European seabass, Dicentrarchus labrax an important species, both for fisheries and aquaculture.

Morphological characteristics of microenvironment in the human thymus during fetal development

BACKGROUND

The thymus is a key organ for the development of T cells. T cell precursors first migrate from the bone marrow to the thymus. During maturation, these precursors require interactions with various types of cells that form the thymic microenvironment, such as epithelial, mesenchymal, and other immune cells not belonging to the T lineage. The aim of this study was to examine the changes in the number and diameter of Hassall's corpuscles, as well as the density and distribution of epithelial cells (p63+) and macrophages (CD68+).

METHODS

Twenty-five fetal thymus samples were examined, divided into five groups according to gestational age. The samples were processed using standard histological methods and immunohistochemical staining.

RESULTS

The study showed that the number and diameter of Hassall's corpuscles gradually increased during fetal development, with a significant increase from the 14th to the 38th gestational week. The average diameter of Hassall's corpuscles was largest in the age group of 34-38 weeks. The density of p63 + epithelial cells decreased in correlation with gestational week, while the density of CD68 + macrophages significantly increased, particularly in the thymic medulla, towards the end of the fetal period.

CONCLUSIONS

An increase in the number and size of Hassall's corpuscles during fetal development was recorded, while the density of epithelial cells decreased and the density of macrophages increased.

The effect of abnormal lipid metabolism on immunosenescence of the colonic lamina propria in mice of different ages

Immunosenescence is an age-associated change in immunological function. The intestinal mucosal immune system is considered the largest immune system in the human body, and its immunosenescence is closely related to the occurrence and development of many diseases. In recent years, studies have identified a crucial correlation between abnormal lipid metabolism induced by high-fat diet (HFD) and immunity, but the effect and mechanism of HFD on colonic mucosal immunosenescence are still unclear. In this study, we established an abnormal lipid metabolism model at different ages by feeding male wild-type mice HFD and compared the immunosenescence of the spleen, which reflects systemic immunity, and the colonic lamina propria (LP), which reflects local immunity. The results showed that HFD could lead to abnormal lipid metabolism at different ages, accelerate systemic and local immunosenescence, and increase the expression of inflammatory factors in colonic tissue. The levels of abnormal biochemical indicators induced by HFD were closely related to the proportions of T cell subsets associated with immunosenescence. Overall, the results showed that HFD had the most significant impact on aged mice. This study provides new ideas for further understanding the relationship between abnormal lipid metabolism and intestinal mucosal immunosenescence.

Primary and secondary defects of the thymus

The thymus is the primary site of T-cell development, enabling generation, and selection of a diverse repertoire of T cells that recognize non-self, whilst remaining tolerant to self- antigens. Severe congenital disorders of thymic development (athymia) can be fatal if left untreated due to infections, and thymic tissue implantation is the only cure. While newborn screening for severe combined immune deficiency has allowed improved detection at birth of congenital athymia, thymic disorders acquired later in life are still underrecognized and assessing the quality of thymic function in such conditions remains a challenge. The thymus is sensitive to injury elicited from a variety of endogenous and exogenous factors, and its self-renewal capacity decreases with age. Secondary and age-related forms of thymic dysfunction may lead to an increased risk of infections, malignancy, and autoimmunity. Promising results have been obtained in preclinical models and clinical trials upon administration of soluble factors promoting thymic regeneration, but to date no therapy is approved for clinical use. In this review we provide a background on thymus development, function, and age-related involution. We discuss disease mechanisms, diagnostic, and therapeutic approaches for primary and secondary thymic defects.

Investigating Thymic Epithelial Cell Diversity Using Systems Biology

The thymus is an intricate organ consisting of a diverse population of thymic epithelial cells (TECs). Cortical and medullary TECs and their subpopulations have distinct roles in coordinating the development and selection of functionally competent and self-tolerant T cells. Recent advances made in technologies such as single-cell RNA sequencing have made it possible to investigate and resolve the heterogeneity in TECs. These findings have provided further understanding of the molecular mechanisms regulating TEC function and expression of tissue-restricted Ags. In this brief review, we focus on the newly characterized subsets of TECs and their diversity in relation to their functions in supporting T cell development. We also discuss recent discoveries in expression of self-antigens in the context of TEC development as well as the cellular and molecular changes occurring during embryonic development to thymic involution.

A Blood-Based Molecular Clock for Biological Age Estimation

In the last decade, extensive efforts have been made to identify biomarkers of biological age. DNA methylation levels of ELOVL fatty acid elongase 2 (ELOVL2) and the signal joint T-cell receptor rearrangement excision circles (sjTRECs) represent the most promising candidates. Although these two non-redundant biomarkers echo important biological aspects of the ageing process in humans, a well-validated molecular clock exploiting these powerful candidates has not yet been formulated. The present study aimed to develop a more accurate molecular clock in a sample of 194 Italian individuals by re-analyzing the previously obtained EVOLV2 methylation data together with the amount of sjTRECs in the same blood samples. The proposed model showed a high prediction accuracy both in younger individuals with an error of about 2.5 years and in older subjects where a relatively low error was observed if compared with those reported in previously published studies. In conclusion, an easy, cost-effective and reliable model to measure the individual rate and the quality of aging in human population has been proposed. Further studies are required to validate the model and to extend its use in an applicative context.

Immune senescence and periodontitis: From mechanism to therapy

Periodontitis is one of the most prevalent infectious inflammatory diseases, characterized by irreversible destruction of the supporting tissues of teeth, which is correlated with a greater risk of multiple systemic diseases, thus regarded as a major health concern. Dysregulation between periodontal microbial community and host immunity is considered to be the leading cause of periodontitis. Comprehensive studies have unveiled the double-edged role of immune response in the development of periodontitis. Immune senescence, which is described as age-related alterations in immune system, including a diminished immune response to endogenous and exogenous stimuli, a decline in the efficiency of immune protection, and even failure in immunity build-up after vaccination, leads to the increased susceptibility to infection. Recently, the intimate relationship between immune senescence and periodontitis has come into focus, especially in the aging population. In this review, both periodontal immunity and immune senescence will be fully introduced, especially their roles in the pathology and progression of periodontitis. Furthermore, novel immunotherapies targeting immune senescence are presented to provide potential targets for research and clinical intervention in the future.

Growth Hormone Stimulates Murine Macrophage Migration during Aging

BACKGROUND

Age-related impairments in macrophage functions have important consequences for the health of the elderly population. The aging process is also accompanied by a reduction in several hormones, including growth hormone (GH). Previous studies have shown that this hormone can affect macrophage activity in young individuals; however, the biological effects of GH stimulation on macrophages during aging have not yet been elucidated.

OBJECTIVE

The aim of this work was to investigate the in vitro effects of GH on peritoneal macrophages from aged mice.

METHODS

Peritoneal macrophages isolated from young (4 months-old) and old (12-15 months-old) mice were treated in vitro with 100 ng/mL of GH for 24 hours. After treatment, cells were analysed for cell morphology, reactive oxygen species (ROS) production, expression of integrins, cell adhesion to extracellular matrix molecules, and migration in transwell chambers.

RESULTS

Although GH-treated cells from old mice exhibited decreased ROS production, we did not observe the effects of GH on macrophage morphology or macrophage phagocytic activity in young and old mice-derived cell cultures. Macrophages from old mice had increased adhesion to laminin and fibronectin substrates, as did cells obtained from young mice treated with GH, but no change was observed in the expression of integrin receptors. Furthermore, cells from old mice exhibited increased migration compared to young mice and a significant increase in macrophage migration was observed under GH stimulation.

CONCLUSION

Our results showed that GH can interfere with the motility of macrophages from old mice, advancing our understanding of the interactions between the immune and neuroendocrine systems during aging.

Age-related thymic involution: Mechanisms and functional impact

The thymus is the primary immune organ responsible for generating self‐tolerant and immunocompetent T cells. However, the thymus gradually involutes during early life resulting in declined naïve T‐cell production, a process known as age‐related thymic involution. Thymic involution has many negative impacts on immune function including reduced pathogen resistance, high autoimmunity incidence, and attenuated tumor immunosurveillance. Age‐related thymic involution leads to a gradual reduction in thymic cellularity and thymic stromal microenvironment disruption, including loss of definite cortical‐medullary junctions, reduction of cortical thymic epithelial cells and medullary thymic epithelial cells, fibroblast expansion, and an increase in perivascular space. The compromised thymic microenvironment in aged individuals substantially disturbs thymocyte development and differentiation. Age‐related thymic involution is regulated by many transcription factors, micro RNAs, growth factors, cytokines, and other factors. In this review, we summarize the current understanding of age‐related thymic involution mechanisms and effects.

Understanding the role of host metabolites in the induction of immune senescence: Future strategies for keeping the ageing population healthy

Advancing age is accompanied by significant remodelling of the immune system, termed immune senescence, and increased systemic inflammation, termed inflammageing, both of which contribute towards an increased risk of developing chronic diseases in old age. Age-associated alterations in metabolic homeostasis have been linked with changes in a range of physiological functions, but their effects on immune senescence remains poorly understood. In this article, we review the recent literature to formulate hypotheses as to how an age-associated dysfunctional metabolism, driven by an accumulation of key host metabolites (saturated fatty acids, cholesterol, ceramides and lactate) and loss of other metabolites (glutamine, tryptophan and short-chain fatty acids), might play a role in driving immune senescence and inflammageing, ultimately leading to diseases of old age. We also highlight the potential use of metabolic immunotherapeutic strategies targeting these processes in counteracting immune senescence and restoring immune homeostasis in older adults. LINKED ARTICLES: This article is part of a themed issue on Inflammation, Repair and Ageing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.9/issuetoc.

Fish Collagen Peptides Protect against Cisplatin-Induced Cytotoxicity and Oxidative Injury by Inhibiting MAPK Signaling Pathways in Mouse Thymic Epithelial Cells

Thymic epithelial cells (TECs) account for the most abundant and dominant stromal component of the thymus, where T cells mature. Oxidative- or cytotoxic-stress associated injury in TECs, a significant and common problem in many clinical settings, may cause a compromised thymopoietic capacity of TECs, resulting in clinically significant immune deficiency disorders or impairment in the adaptive immune response in the body. The present study demonstrated that fish collagen peptides (FCP) increase cell viability, reduce intracellular levels of reactive oxygen species (ROS), and impede apoptosis by repressing the expression of Bax and Bad and the release of cytochrome c, and by upregulating the expression of Bcl-2 and Bcl-xL in cisplatin-treated TECs. These inhibitory effects of FCP on TEC damage occur via the suppression of ROS generation and MAPK (p38 MAPK, JNK, and ERK) activity. Taken together, our data suggest that FCP can be used as a promising protective agent against cytotoxic insults- or ROS-mediated TEC injury. Furthermore, our findings provide new insights into a therapeutic approach for the future application of FCP in the prevention and treatment of various types of oxidative- or cytotoxic stress-related cell injury in TECs as well as age-related or acute thymus involution.

The intervention on aging system: A classification model, the requirement for five novel categories

Aging is widely considered an immovable fact of life. Cultural conditioning has ensured that therapeutics for extreme human lifespans are considered out of reach technologies. However, longevity therapies such as stem cell replacement, fasting, gene therapies, fasting mimetics such as metformin and rapamycin, regulation and tissue reprogramming with OSK transcription factors, blood dilution, metabolic pathway engineering, reversal of epigenetic drift, heterochronic parabiosis, coenzyme replacement technologies (nicotinamide adenine dinucleotide) and a plethora of other established sciences are showing great potential at slowing down the rate at which tissues enter dysfunction. Recent discoveries have shed light on major mysteries of the aging process. Longevity-based discoveries are not only landing quickly, but therapies to prevent or reverse those drivers of aging are also being devised regularly and this is opening up an entirely new industry, the longevity industry. This presents the requirement for a new classification system where subjects can be divided into specific groups based on their potential for mortality. This system also enables the public to target which class of this classification system they wish to be on. Moving the population on the classification system to become more disease resistant holds great benefit for society and governments as a whole.

Thymax, a gross thymic extract, exerts cell cycle arrest and apoptosis in Ehrlich ascites carcinoma in vivo

Thymax is a gross thymic extract that has been shown to induce apoptosis in vitro for human breast cancer cells. Here we examine Thymax's ability to induce apoptosis in animals bearing Ehrlich ascites carcinoma (EAC). Thymax was administered six days/week orally to mice (5.45 mg/kg body weight) beginning either 14 days prior to EAC inoculation or 9 days post inoculation; treatment continued for 30 days post inoculation. Pretreatment of mice with Thymax markedly delayed tumor growth and reduced tumor incidence by 38.9%, and tumor volumes relative to untreated controls were suppressed by 90.5% and 55.0% for pre- and post-inoculation groups, respectively. Treatment with Thymax inhibited cellular proliferation by decreasing the expression of tumor markers Ki-67, PCNA, and Cyclin D1 in cancer cells and increasing the expression of p21 and p27. This was associated with the ability of Thymax to arrest the cell cycle of EAC cells in the G0/G1 phase and to induce apoptosis, as indicated by a significant increase in the sub-G1 phase's percentage of hypodiploid cells and further affirmed by DNA fragmentation and Annexin V/propidium iodide staining. In addition, Thymax exerted its apoptotic effect in EAC cancer cells through a mitochondrial-dependent pathway, as evidenced by an increased Bax/Bcl-2 ratio, up-regulation of p53 expression, and activation of caspase-3. We conclude that Thymax supplementation enhances tumor cell demise by arresting the cell cycle and inducing apoptosis. These data suggest that Thymax could be a new adjuvant for breast cancer treatment.

Probiotic Consumption Boosts Thymus in Obesity and Senescence Mouse Models

The ability of the immune system to respond to different pathogens throughout life requires the constant production and selection of T cells in the thymus. This immune organ is very sensitive to age, infectious processes and nutrition disorders (obesity and malnutrition). Several studies have shown that the incorporation of some probiotic bacteria or probiotic fermented milk in the diet has beneficial effects, not only at the intestinal level but also on distant mucosal tissues, improving the architecture of the thymus in a malnutrition model. The aim of the present study was to determine whether supplementation with the probiotic strain Lactobacillus casei CRL 431 and/or its cell wall could improve body weight, intestinal microbiota and thymus structure and function in both obese and aging mice. We evaluated probiotic administration to BALB/c mice in 2 experimental mouse models: obesity and senescence, including mice of different ages (21, 28, 45, 90 and 180 days). Changes in thymus size and histology were recorded. T-lymphocyte population and cytokine production were also determined. The consumption of probiotics improved the cortical/medullary ratio, the production and regulation of cytokines and the recovery of mature T-lymphocyte populations of the thymus in obese and old mice. Probiotic incorporation into the diet could not only modulate the immune system but also lead to thymus function recovery, thus improving quality of life.

Multilocular Thymic Cyst in a Patient with Untreated HIV/AIDS: Case Report and Review of the Literature

BACKGROUND

Multilocular thymic cysts (MTCs) in adults with human immunodeficiency virus (HIV) are rarely reported.

CASE PRESENTATION

We describe a case of symptomatic MTC in a male with untreated HIV. A presumptive diagnosis was established based on radiographic imaging and biopsy. Pathologic diagnosis and exclusion of malignancy were ultimately confirmed the following thymectomy. In conjunction with starting antiretroviral therapy, the patient recovered well post-operatively with a resolution of his presenting symptoms.

CONCLUSION

Our case report and review of the literature serve to highlight MTCs as an important clinical entity occurring in persons with HIV.

Age-Associated Characteristics of CD4+ T-Cell Composition in Patients with Atherosclerosis

Background. We aimed to analyze the contents of the main CD4+ T-cell subsets in patients with atherosclerosis (AS) depending on age. Methods. Male patients with coronary and/or carotid AS, who are non-smokers, and who are receiving statins were divided into three age groups (I—<55 y.o. (n = 23), II—55–64 y.o. (n = 42), III—≥65 y.o. (n = 46)). Leukocyte phenotyping was performed by direct immunofluorescence and flow cytometry. For intracellular cytokine detection, blood mononuclear cells were pre-activated with phorbol 12-myristate 13-acetate and ionomycin in the presence of an intracellular vesicle transport blocker monensin. Results. The groups did not differ in traditional CVD risk factors and AS severity. The content of CD4+ T-cells was lower in group III and II than in group I. The content of CD4+CD25high Treg was lower in group III than in groups I and II. No differences in the quantities of the primed CD39+CD45RA− and CD278high Treg, CD4+INFγ+ Th1, CD4+IL17+ Th17, and CD4+IL17+INFγ+ Th1/17 were observed. There were negative correlations between the values of CD4+ T-cells, CD4+CD45RA+ T-cells, CD4+CD25high Treg, CD4+CD25highCD45RA+ Treg, and age. Conclusion. In patients with AS, the age-related depletion of naive CD4+ T-cells also extends to the regulatory compartment. This phenomenon should be considered when studying the impact of the immune cells on the progression of AS.

Ageing of the gut microbiome: Potential influences on immune senescence and inflammageing

Advancing age is accompanied by changes in the gut microbiota characterised by a loss of beneficial commensal microbes that is driven by intrinsic and extrinsic factors such as diet, medications, sedentary behaviour and chronic health conditions. Concurrently, ageing is accompanied by an impaired ability to mount a robust immune response, termed immunesenescence, and age-associated inflammation, termed inflammaging. The microbiome has been proposed to impact the immune system and is a potential determinant of healthy aging. In this review we summarise the knowledge on the impact of ageing on microbial dysbiosis, intestinal permeability, inflammaging, and the immune system and investigate whether dysbiosis of the gut microbiota could be a potential mechanism underlying the decline in immune function, overall health and longevity with advancing age. Furthermore, we examine the potential of altering the gut microbiome composition as a novel intervention strategy to reverse the immune ageing clock and possibly support overall good health during old age.

Sex Differences in the Immune System Become Evident in the Perinatal Period in the Four Core Genotypes Mouse

We have used the four core genotypes (FCG) mouse model, which allows a distinction between effects of gonadal secretions and chromosomal complement, to determine when sex differences in the immune system first appear and what influences their development. Using splenic T cell number as a measure that could be applied to neonates with as yet immature immune responses, we found no differences among the four genotypes at postnatal day 1, but by day 7, clear sex differences were observed. These sex differences were unexpectedly independent of chromosomal complement and similar in degree to gonadectomized FCG adults: both neonatal and gonadectomized adult females (XX and XY) showed 2-fold the number of CD4+ and 7-fold the number of CD8+ T cells versus their male (XX and XY) counterparts. Appearance of this long-lived sex difference between days 1 and 7 suggested a role for the male-specific perinatal surge of testicular testosterone. Interference with the testosterone surge significantly de-masculinized the male CD4+, but not CD8+ splenic profile. Treatment of neonates demonstrated elevated testosterone limited mature cell egress from the thymus, whereas estradiol reduced splenic T cell seeding in females. Neonatal male splenic epithelium/stroma expressed aromatase mRNA, suggesting capacity for splenic conversion of perinatal testosterone into estradiol in males, which, similar to administration of estradiol in females, would result in reduced splenic T cell seeding. These sex steroid effects affected both CD4+ and CD8+ cells and yet interference with the testosterone surge only significantly de-masculinized the splenic content of CD4+ cells. For CD8+ cells, male cells in the thymus were also found to express one third the density of sphingosine-1-phosphate thymic egress receptors per cell compared to female, a male characteristic most likely an indirect result of Sry expression. Interestingly, the data also support a previously unrecognized role for non-gonadal estradiol in the promotion of intra-thymic cell proliferation in neonates of both sexes. Microarray analysis suggested the thymic epithelium/stroma as the source of this hormone. We conclude that some immune sex differences appear long before puberty and more than one mechanism contributes to differential numbers and distribution of T cells.

Acute Myeloid Leukemia: Is It T Time?

Acute myeloid leukemia (AML) is a heterogeneous disease driven by impaired differentiation of hematopoietic primitive cells toward myeloid lineages (monocytes, granulocytes, red blood cells, platelets), leading to expansion and accumulation of "stem" and/or "progenitor"-like or differentiated leukemic cells in the bone marrow and blood. AML progression alters the bone marrow microenvironment and inhibits hematopoiesis' proper functioning, causing sustained cytopenia and immunodeficiency. This review describes how the AML microenvironment influences lymphoid lineages, particularly T lymphocytes that originate from the thymus and orchestrate adaptive immune response. We focus on the elderly population, which is mainly affected by this pathology. We discuss how a permissive AML microenvironment can alter and even worsen the thymic function, T cells' peripheral homeostasis, phenotype, and functions. Based on the recent findings on the mechanisms supporting that AML induces quantitative and qualitative changes in T cells, we suggest and summarize current immunotherapeutic strategies and challenges to overcome these anomalies to improve the anti-leukemic immune response and the clinical outcome of patients.

Defective dystrophic thymus determines degenerative changes in skeletal muscle

In Duchenne muscular dystrophy (DMD), sarcolemma fragility and myofiber necrosis produce cellular debris that attract inflammatory cells. Macrophages and T-lymphocytes infiltrate muscles in response to damage-associated molecular pattern signalling and the release of TNF-α, TGF-β and interleukins prevent skeletal muscle improvement from the inflammation. This immunological scenario was extended by the discovery of a specific response to muscle antigens and a role for regulatory T cells (Tregs) in muscle regeneration. Normally, autoimmunity is avoided by autoreactive T-lymphocyte deletion within thymus, while in the periphery Tregs monitor effector T-cells escaping from central regulatory control. Here, we report impairment of thymus architecture of mdx mice together with decreased expression of ghrelin, autophagy dysfunction and AIRE down-regulation. Transplantation of dystrophic thymus in recipient nude mice determine the up-regulation of inflammatory/fibrotic markers, marked metabolic breakdown that leads to muscle atrophy and loss of force. These results indicate that involution of dystrophic thymus exacerbates muscular dystrophy by altering central immune tolerance.

Thymic Aging May Be Associated with COVID-19 Pathophysiology in the Elderly

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the global pandemic of coronavirus disease 2019 (COVID-19) and particularly exhibits severe symptoms and mortality in elderly individuals. Mounting evidence shows that the characteristics of the age-related clinical severity of COVID-19 are attributed to insufficient antiviral immune function and excessive self-damaging immune reaction, involving T cell immunity and associated with pre-existing basal inflammation in the elderly. Age-related changes to T cell immunosenescence is characterized by not only restricted T cell receptor (TCR) repertoire diversity, accumulation of exhausted and/or senescent memory T cells, but also by increased self-reactive T cell- and innate immune cell-induced chronic inflammation, and accumulated and functionally enhanced polyclonal regulatory T (Treg) cells. Many of these changes can be traced back to age-related thymic involution/degeneration. How these changes contribute to differences in COVID-19 disease severity between young and aged patients is an urgent area of investigation. Therefore, we attempt to connect various clues in this field by reviewing and discussing recent research on the role of the thymus and T cells in COVID-19 immunity during aging (a synergistic effect of diminished responses to pathogens and enhanced responses to self) impacting age-related clinical severity of COVID-19. We also address potential combinational strategies to rejuvenate multiple aging-impacted immune system checkpoints by revival of aged thymic function, boosting peripheral T cell responses, and alleviating chronic, basal inflammation to improve the efficiency of anti-SARS-CoV-2 immunity and vaccination in the elderly.

Hypothalamic aging and hormones

It is the heterogeneous changes of hypothalamic functions that determine the chronological sequence of aging in mammals. Recently, it was hypothesized by Cai the decrease in slow-wave sleep (SWS) resulting from skin aging as responsible for the degeneration of hypothalamic suprachiasmatic nucleus (SCN). It was soon hypothesized by the European people in television that the increase in body fat as responsible for the degeneration of male preoptic sexually dimorphic nucleus (SDN-POA), via the aromatase converting testosterone to estradiol as proposed by Cohen. It is the hypothalamic paraventricular nucleus (PVN) that remains unchanged in neuron number during aging for psychological stress. In this chapter, it is briefly reviewed more manifestations of hypothalamic related mammalian aging processes, including (1) the aging of ovary by lipid, estradiol and hypothalamus; (2) the aging of muscle, stomach, intestine, thymus, and the later aging of brain, regulated by growth hormone/insulin-like growth factor 1(GH/IGF1); (3) the cardiovascular hypertension from PVN activation, the bone and other peripheral aging by psychological stress, and that of kidney by vasopressin. It is classified these aging processes by the primary regulation from one of the three hypothalamic nuclei, although still necessary to investigate and supplement their secondary regulation by the hypothalamic nuclei in future. It is the hypothalamic structural changes that shift the functional balance among these three hypothalamic systems toward aging.

Thymus-Pineal Gland Axis: Revisiting Its Role in Human Life and Ageing

For years the thymus gland (TG) and the pineal gland (PG) have been subject of increasingly in-depth studies, but only recently a link that can associate the activities of the two organs has been identified. Considering, on the one hand, the well-known immune activity of thymus and, on the other, the increasingly emerging immunological roles of circadian oscillators and the rhythmically secreted main pineal product, melatonin, many studies aimed to analyse the possible existence of an interaction between these two systems. Moreover, data confirmed that the immune system is functionally associated with the nervous and endocrine systems determining an integrated dynamic network. In addition, recent researches showed a similar, characteristic involution process both in TG and PG. Since the second half of the 20th century, evidence led to the definition of an effectively interacting thymus-pineal axis (TG-PG axis), but much has to be done. In this sense, the aim of this review is to summarize what is actually known about this topic, focusing on the impact of the TG-PG axis on human life and ageing. We would like to give more emphasis to the implications of this dynamical interaction in a possible therapeutic strategy for human health. Moreover, we focused on all the products of TG and PG in order to collect what is known about the role of peptides other than melatonin. The results available today are often unclear and not linear. These peptides have not been well studied and defined over the years. In this review we hope to awake the interest of the scientific community in them and in their future pharmacological applications.

miR-205-5p inhibits thymic epithelial cell proliferation via FA2H-TFAP2A feedback regulation in age-associated thymus involution

Thymic epithelial cells (TECs) are essential regulators of T cell development and selection. microRNAs (miRNAs) play critical roles in regulating TECs proliferation during thymus involution. miR-205-5p is highly expressed in TECs and increases with age. However, the function and potential mechanism of miR-205-5p in TECs are not clear. miRNA expression was profiled using TECs from male and female mice at 1 and 3 months old. A total of 325 differentially expressed miRNAs (DEMs) were detected at different ages in two sexes. 24 of the DEMs had the same trend between males and females. Among them, miR-205-5p had the highest fold change. Our results showed that the expression of miR-205-5p was dramatically increased in TECs from 1 to 9 months old mice. miR-205-5p mimic inhibited TECs proliferation. Moreover, we confirmed that Fa2h was the direct target gene of miR-205-5p and FA2H was significantly decreased in TECs with increased expression of miR-205-5p. Silencing of Fa2h inhibited TECs proliferation. Furthermore, we found that the expression of Tfap2a could be promoted by FA2H and that TFAP2A could interact with miR-205-5p in TECs. Overall, miR-205-5p is an important regulator of TECs proliferation and regulates age-associated thymus involution via the miR-205-5p-FA2H-TFAP2A feedback regulatory circuit. miR-205-5p might act as a potential biomarker in TECs for age-related thymus involution.

Thymic Epithelial Cells Contribute to Thymopoiesis and T Cell Development

The thymus is the primary lymphoid organ responsible for the generation and maturation of T cells. Thymic epithelial cells (TECs) account for the majority of thymic stromal components. They are further divided into cortical and medullary TECs based on their localization within the thymus and are involved in positive and negative selection, respectively. Establishment of self-tolerance in the thymus depends on promiscuous gene expression (pGE) of tissue-restricted antigens (TRAs) by TECs. Such pGE is co-controlled by the autoimmune regulator (Aire) and forebrain embryonic zinc fingerlike protein 2 (Fezf2). Over the past two decades, research has found that TECs contribute greatly to thymopoiesis and T cell development. In turn, signals from T cells regulate the differentiation and maturation of TECs. Several signaling pathways essential for the development and maturation of TECs have been discovered. New technology and animal models have provided important observations on TEC differentiation, development, and thymopoiesis. In this review, we will discuss recent advances in classification, development, and maintenance of TECs and mechanisms that control TEC functions during thymic involution and central tolerance.

CD147 deficiency in T cells prevents thymic involution by inhibiting the EMT process in TECs in the presence of TGFβ

Thymic involution during aging is a major cause of decreased T-cell production and reduced immunity. Here, we show that the loss of CD147 on T cells prevents thymic senescence, resulting in slowed shrinkage of the thymus with age and increased production of naive T cells. This phenotype is the result of slowing of the epithelial–mesenchymal transition (EMT) process in thymic epithelial cells (TECs), which eventually leads to reduced adipocyte accumulation. In an in vitro coculture system, we found that TGFβ is an important factor in the EMT process in TECs and that it can reduce the expression of E-cadherin through p-Smad2/FoxC2 signaling. Moreover, CD147 on T cells can accelerate the decline in E-cadherin expression by interacting with Annexin A2 on TECs. In the presence of TGFβ, Annexin A2 and E-cadherin colocalize on TECs. However, CD147 on T cells competitively binds to Annexin A2 on TECs, leading to the isolation of E-cadherin. Then, the isolated E-cadherin is easily phosphorylated by phosphorylated Src kinase, the phosphorylation of which was induced by TGFβ, and finally, p-E-cadherin is degraded. Thus, in the thymus, the interaction between T cells and TECs contributes to thymic involution with age. In this study, we illuminate the mechanism underlying the triggering of the EMT process in TECs and show that inhibiting TGFβ and/or CD147 may serve as a strategy to hinder age-related thymic involution.

Reversal of epigenetic aging and immunosenescent trends in humans

Epigenetic “clocks” can now surpass chronological age in accuracy for estimating biological age. Here, we use four such age estimators to show that epigenetic aging can be reversed in humans. Using a protocol intended to regenerate the thymus, we observed protective immunological changes, improved risk indices for many age‐related diseases, and a mean epigenetic age approximately 1.5 years less than baseline after 1 year of treatment (−2.5‐year change compared to no treatment at the end of the study). The rate of epigenetic aging reversal relative to chronological age accelerated from −1.6 year/year from 0–9 month to −6.5 year/year from 9–12 month. The GrimAge predictor of human morbidity and mortality showed a 2‐year decrease in epigenetic vs. chronological age that persisted six months after discontinuing treatment. This is to our knowledge the first report of an increase, based on an epigenetic age estimator, in predicted human lifespan by means of a currently accessible aging intervention.

How Could We Slow or Reverse the Human Aging Process and Extend the Healthy Life Span with Heterochronous Autologous Hematopoietic Stem Cell Transplantation

The senescence of the immune system contributes considerably to the age-related diseases that are the main causes of death after the age of 65. In this study, we present an appealing option for the prevention of immune senescence and slowing or reversing the aging process, which can be achieved by heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow stem cells are collected from donors while young, cryopreserved and stored for a long period, and reinfused at a later time when indicated. After reinfusion and homing, these young HSCs could participate in normal hemato- and immunopoiesis and improve several immune functions by expanding the immune- as well as hematopoietic cell repertoire. Several animal studies have already confirmed the feasibility of this procedure, which extended the longevity of the treated animals. If translated to human medicine, haHSCT could prevent or mitigate age-related immune defects and extend the healthy life span. In this review, we describe the concept of haHSCT, recent studies that confirm its feasibility, and discuss the further research needed to translate this heterochronous methodology.

Label-free quantitative proteomics identifies transforming growth factor β1 (TGF-β1) as an inhibitor of adipogenic transformation in OP9-DL1 cells and primary thymic stromal cells

Background

Adipocyte accumulation is a predominant feature of age-related thymic involution, but the mechanisms responsible for thymic adipogenesis remain to be elucidated. The aim of this study was to identify key regulators in thymic adipogenesis. We used rosiglitazone, a potent peroxisome proliferator-activated receptor γ (PPARγ) agonist, to induce adipogenic differentiation of OP9-DL1 cells, and investigated the differentially expressed proteins during adipogenic differentiation by using label-free quantitative proteomics. Furthermore, the effects of transforming growth factor β1 (TGF-β1) on rosiglitazone-induced adipogenic differentiation of OP9-DL1 cells as well as the underlying mechanisms were also investigated.

Results

Proteomic analysis identified 139 proteins differed significantly in rosiglitazone-treated cells compared with dimethyl sulphoxide (DMSO)-treated cells. Rosiglitazone-induced adipogenic differentiation was inhibited by TGF-β1 treatment in OP9-DL1 cells and primary thymic stromal cells. Real-time PCR analysis showed significant increases in PPARγ and fatty acid binding protein 4 mRNA levels in rosiglitazone-treated cells, which were inhibited by TGF-β1 treatment. TGF-β1 down-regulated PPARγ expression at both mRNA and protein levels in OP9-DL1 cells. Chromatin immunoprecipitation analysis demonstrated that TGF-β1 enhanced the binding of Smad2/3 and histone deacetylase 1, but reduced the binding of H3K14ac to the promoter of PPARγ gene. TGF-β1 partially reversed the inhibitory effects of rosiglitazone on the expression of Axin2 and β-catenin protein levels. TGF-β1 inhibited rosiglitazone-induced adipogenic transformation in OP9-DL1 cells by down-regulation of PPARγ and activation of the canonical Wnt/β-catenin signaling pathway.

Conclusion

Taken together, activation of TGF-β pathway may serve as a useful strategy to prevent thymic adiposity in age-related thymic involution.

Electronic supplementary material

The online version of this article (10.1186/s13578-019-0311-1) contains supplementary material, which is available to authorized users.

Th1 Biased Progressive Autoimmunity in Aged Aire-Deficient Mice Accelerated Thymic Epithelial Cell Senescence

Although autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, are frequently associated with premature aging of the thymus, a direct link is missing between autoimmunity and thymic atrophy. Here we monitored the progression of thymic involution in Aire-deficient mice, in which defective negative selection causes spontaneous and progressive development of autoimmunity. In young and middle-aged mice, Aire deficiency appeared to be protective as supported by the reduced β-gal⁺ epithelial cells and the enhanced thymic output. However, once the autoimmune phenotype was fully developed in aged Aire-deficient mice, their thymuses underwent accelerated involution. In comparison to the age-matched wildtype littermates, old Aire-deficient mice showed lower numbers of total thymocytes and recent thymic emigrants but more β-gal⁺ thymic epithelial cells. This phenomenon may partly be attributable to the increased number of activated Th1 cells homing to the thymus. This speculation was further supported by the enhanced thymic aging following repeated challenges with complete Freund’s adjuvant immunization. Taken together, the present study highlights a unique mechanism by which autoimmunity facilitates the senescence of thymic epithelial cells through returning Th1 cells.

Restoring thymic function: Then and now

Thymic vulnerability, a leading cause of defective immunity, was discovered decades ago. To date, several strategies have been investigated to unveil any immunorestorative capacities they might confer. Studies exploiting castration, transplantation, adoptive cell therapies, hormones/growth factors, and cytokines have demonstrated enhanced in vitro and in vivo thymopoiesis, albeit with clinical restrictions. In this review, we will dissect the thymus on a physiological and pathological level and discuss the pros and cons of several strategies esteemed thymotrophic from a pre-clinical perspective. Finally, we will shed light on interleukin (IL)-21, a pharmacologically-promising cytokine with a significant thymotrophic nature, and elaborate on its potential clinical efficacy and safety in immune-deficient subjects.

Notch1 Inhibits Rosiglitazone-Induced Adipogenic Differentiation in Primary Thymic Stromal Cells

Adipocyte deposition is believed to be a primary characteristic of age-related thymic involution. Herein, we cultured primary thymic stromal cells (TSCs), used rosiglitazone, a potent peroxisome proliferator-activated receptor γ (PPARγ) agonist, to induce adipogenic differentiation, and investigated the differentially expressed genes during adipogenic differentiation by using RNA-sequencing analysis. Furthermore, the effects of Notch1 on rosiglitazone-induced adipogenic differentiation of TSCs as well as the underlying mechanisms were also investigated. As a result, we identified a total of 1737 differentially expressed genes, among which 965 genes were up-regulated and 772 genes were down-regulated in rosiglitazone-treated cells compared with control cells. Gene ontology (GO) enrichment analysis showed that the GO terms were enriched in metabolic process, intracellular, and protein binding. Kyoto encyclopedia of genes and genomes (KEGG) analysis showed that a number of pathways, including ubiquitin mediated proteolysis, PPAR signaling pathway, and mammalian target of rapamycin (mTOR) signaling pathway were predominantly over-represented. Meanwhile, overexpression of Notch1 suppressed and inhibition of Notch1 promoted rosiglitazone-induced adipogenic differentiation in TSCs, and the pro-adipogenic effects of the Notch inhibitor DAPT were associated with the activation of autophagy. Taken together, our results suggest that Notch1 is a key regulator in thymic adipogenesis and may serve as a potential target to hinder thymic adiposity in age-related thymic involution.

Elimination of CD4lowHLA-G+ T cells overcomes castration-resistance in prostate cancer therapy

Androgen deprivation therapy (ADT) is a main treatment for prostate cancer (PCa) but the disease often recurs and becomes castration-resistant in nearly all patients. Recent data implicate the involvement of immune cells in the development of this castration-resistant prostate cancer (CRPC). In particular, T cells have been found to be expanded in both PCa patients and mouse models shortly after androgen deprivation. However, whether or which of the T cell subtypes play an important role during the development of CRPC is unknown. Here we identified a novel population of CD4^lowHLA-G⁺ T cells that undergo significant expansion in PCa patients after ADT. In mouse PCa models, a similar CD4^low T cell population expands during the early stages of CRPC onset. These cells are identified as IL-4-expressing T_H17 cells, and are shown to be associated with CRPC onset in patients and essential for the development of CRPC in mouse models. Mechanistically, CD4^lowHLA-G⁺ T cells drive androgen-independent growth of prostate cancer cells by modulating the activity and migration of CD11b^lowF4/80^hi macrophages. Furthermore, following androgen deprivation, elevated PGE₂-EP2 signaling inhibited the expression of CD4 in thymocytes, and subsequently induced the polarization of CD4^low naïve T cells towards the IL-4-expressing T_H17 phenotype via up-regulation of IL23R. Therapeutically, inactivating PGE₂ signaling with celecoxib at a time when CD4^lowHLA-G⁺ T cells appeared, but not immediately following androgen deprivation, dramatically suppressed the onset of CRPC. Collectively, our results indicate that an unusual population of CD4^lowHLA-G⁺ T cells is essential for the development of CRPC and point to a new therapeutic avenue of combining ADT with PGE₂ inhibition for the treatment of prostate cancer.

Reversing the immune ageing clock: lifestyle modifications and pharmacological interventions

It is widely accepted that ageing is accompanied by remodelling of the immune system, including reduced numbers of naïve T cells, increased senescent or exhausted T cells, compromise to monocyte, neutrophil and natural killer cell function and an increase in systemic inflammation. In combination these changes result in increased risk of infection, reduced immune memory, reduced immune tolerance and immune surveillance, with significant impacts upon health in old age. More recently it has become clear that the rate of decline in the immune system is malleable and can be influenced by environmental factors such as physical activity as well as pharmacological interventions. This review discusses briefly our current understanding of immunesenescence and then focuses on lifestyle interventions and therapeutic strategies that have been shown to restore immune functioning in aged individuals.

Implications for thymus growth in childhood: histogenesis of cortex and medulla

The increase in autoimmune diseases in recent years has drawn attention back to the thymus, with new approaches to improve and/or restore immune function being investigated. As the primary lymphoid organ responsible for functional T cell development, studies on the pre-/post-natal development of this organ and T lymphocytes in human and other species are of special interest. During our screening studies we observed structures that had not been described or mentioned previously, and named them "epitheliostromal sheaths". Associated with these unique structures were also small attached lobules (possibly reflecting the maturational stages of thymic lobules), which the authors consider as markers of histogenesis and the growth of the organ during early childhood; these findings are thus presented to researchers in this field. Approximately 1000 sections prepared from infantile thymic tissues of partial biopsy specimens were immunostained and examined. Specimens were taken from ten patients (with informed consent) in the age range of 4-9 years who underwent surgery due to congenital cardiovascular anomalies but were otherwise normal. Digital images of interest were captured to describe them in detail. Determining the immunophenotype of the compartments in these newly developing lobules assisted us greatly in defining compartments and their growth order. In summary, our findings suggest a niche-based thymus growth mechanism during childhood. We presented our findings, hoping to provide additional insight to researchers aiming to restore thymus function in adulthood and improve its immunological functions.

Profiling analysis of 17β-estradiol-regulated lncRNAs in mouse thymic epithelial cells

Thymus is the primary organ for T cell differentiation and maturation. Many studies have demonstrated that estrogen plays a crucial role in thymic epithelial cell (TEC) proliferation during thymic involution. LncRNAs are involved in various biological processes; however, estrogen-mediated lncRNA expression in TECs has not been yet reported. To address this question, the mouse medullary thymic epithelial cell line 1 (MTEC1) was treated with 17β-estradiol (E2). By using CCK8 assay and flow cytometry, we found that E2 was able to inhibit viability and proliferation of MTEC1 cells. The expression profiles of lncRNAs in MTEC1 cells with or without E2 treatment were then measured by RNA-Seq, and a total of 962 lncRNAs and 2,469 mRNAs were shown to be differentially expressed. The reliability of RNA-Seq was confirmed by quantitative RT-PCR. Correlation analysis was conducted to investigate the potential function of lncRNAs. According to gene ontology (GO) analysis, differentially expressed lncRNAs were mainly related to cell proliferation, cell cycle and cell apoptosis. KEGG pathway analysis indicated that these lncRNAs were associated with several pathways, namely immunological activity, metabolism and cytokine-cytokine receptor interaction. In conclusion, our study provided a novel direction for studying the relationship between lncRNAs and E2 in the thymus.

Immunoproteasomes Control the Homeostasis of Medullary Thymic Epithelial Cells by Alleviating Proteotoxic Stress

The sole nonredundant role of the thymic medulla is to induce central tolerance, a vital process that depends on promiscuous gene expression (pGE), a unique feature of medullary thymic epithelial cells (mTECs). Although pGE enhances transcription of >3,000 genes in mTECs, its impact on the regulation of protein homeostasis remains unexplored. Here, we report that, because of pGE, mature mTECs synthesize substantially more proteins than other cell types and are exquisitely sensitive to loss of immunoproteasomes (IPs). Indeed, IP deficiency causes proteotoxic stress in mTECs and leads to exhaustion of postnatal mTEC progenitors. Moreover, IP-deficient mice show accelerated thymic involution, which is characterized by a selective loss of mTECs and multiorgan autoimmune manifestations. We conclude that pGE, the quintessential feature of mTECs, is a major burden for the maintenance of proteostasis, which is alleviated by the constitutive expression of IPs in mTECs.

The potential of non-myeloablative heterochronous autologous hematopoietic stem cell transplantation for extending a healthy life span

Aging is a complex multifactorial process, a prominent component being the senescence of the immune system. Consequently, immune-related diseases develop, including atherosclerosis, cancer, and life-threatening infections, which impact on health and longevity. Rejuvenating the aged immune system could mitigate these diseases, thereby contributing to longevity and health. Currently, an appealing option for rejuvenating the immune system is heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow/peripheral blood stem cells are collected during the youth of an individual, cryopreserved, and re-infused when he or she has reached an older age. After infusion, young hematopoietic stem cells can reconstitute the compromised immune system and improve immune function. Several studies using animal models have achieved substantial extension of the life span of animals treated with haHSCT. Therefore, haHSCT could be regarded as a potential procedure for preventing age-related immune defects and extending healthy longevity. In this review, the pros, cons, and future feasibility of this approach are discussed.

Immune signatures associated with mortality differ in elderly populations from different birth cohorts and countries even within northern Europe

Since associations between lifespan and certain simple immune parameters such as T cell proliferative responses to mitogens were reported in the 1970´s, efforts to dissect out immune parameters correlating with morbidity and mortality have sought to define factors predicting individual longevity. Such "immune signatures" associating with defined clinical outcomes would represent biomarkers of "immunosenescence" that might also provide mechanistic insights into the ageing process. Because appropriate immune function is necessary for a healthy old age, a better understanding of immunosenescence contributing to frailty and death might allow interventions to improve personal and public health. Here, we discuss data from our studies in several different European countries and document significant differences between overtly similar populations. These findings draw attention to the marked variation even between presumably quite homogeneous populations, which may be due to the different birth cohorts studied in addition to numerous other variables. Thus, immunological parameters, and presumably many other factors, are sensitive to context-dependent variation, making it currently difficult to extrapolate biomarkers of longevity from any one human population to another.

Where is the greatest impact of uncontrolled HIV infection on AIDS and non-AIDS events in HIV?

OBJECTIVE

The extent to which controlled and uncontrolled HIV interact with ageing, European region of care and calendar year of follow-up is largely unknown.

METHOD

EuroSIDA participants were followed after 1 January 2001 and grouped according to current HIV progression risk; high risk (CD4 cell count ≤350/μl, viral load ≥10 000 copies/ml), low risk (CD4 cell count ≥500 cells/μl, viral load <50 copies/ml) and intermediate (other combinations). Poisson regression investigated interactions between HIV progression risk, age, European region of care and year of follow-up and incidence of AIDS or non-AIDS events.

RESULTS

A total of 16 839 persons were included with 136 688 person-years of follow-up. In persons aged 30 years or less, those at high risk had a six-fold increased incidence of non-AIDS compared with those at low risk, compared with a two-to-three-fold increase in older persons (P = 0.0004, interaction). In Eastern Europe, those at highest risk of non-AIDS had a 12-fold increased incidence compared with a two-to-four-fold difference in all other regions (P = 0.0029, interaction). Those at high risk of non-AIDS during 2001-2004 had a two-fold increased incidence compared with those at low risk, increasing to a five-fold increase between 2013 and 2016 (P < 0.0001, interaction). Differences among high, intermediate and low risk of AIDS were similar across age groups, year of follow-up and Europe (P = 0.57, 0.060 and 0.090, respectively, interaction).

CONCLUSION

Factors other than optimal control of HIV become increasingly important with ageing for predicting non-AIDS, whereas differences across Europe reflect differences in patient management as well as underlying socioeconomic circumstances. The differences between those at high, intermediate and low risk of non-AIDS between 2013 and 2016 likely reflects better quality of care.

Is weak CD4+ gain in the course of suppressive combination antiretroviral therapy for HIV infection a current clinical challenge? A case report and brief review of the literature

Background

Individuals lacking immune recovery during suppressive cART will still represent a clinical issue in the years to come, given the high proportion of HIV-infected subjects introducing therapy late in the course of disease. Understanding the mechanisms underlying poor CD4+ T-cell gain is crucial for the correct clinical management of individuals in this context.

Case presentation

An HIV-infected subject with poor CD4+ T-cell gain in the course of suppressive antiretroviral therapy was extensively investigated to identify the mechanisms behind inadequate CD4+ reconstitution. In particular, we studied the phenotype of circulating T-cells, interleukin-7 signaling in peripheral blood and bone marrow, gut function and microbial translocation markers as well as the composition of the faecal microbiota. Numerous therapeutic interventions ranging from antiretroviral therapy intensification to immunotherapy and anti-hepatitis C virus treatment were also employed in order to target the possible causes of poor immune-recovery.

Conclusions

Poor CD4+ T-cell gain on suppressive antiretroviral therapy is multifactorial and thus represents a clinical challenge. Clinicians should investigate subjects’ immune profile as well as possible causes of chronic antigenic stimulation for the administration of the most appropriate therapeutic strategies in this setting.

The twilight of immunity: emerging concepts in aging of the immune system

Immunosenescence is a series of age-related changes that affect the immune system and, with time, lead to increased vulnerability to infectious diseases. This Review addresses recent developments in the understanding of age-related changes that affect key components of immunity, including the effect of aging on cells of the (mostly adaptive) immune system, on soluble molecules that guide the maintenance and function of the immune system and on lymphoid organs that coordinate both the maintenance of lymphocytes and the initiation of immune responses. I further address the effect of the metagenome and exposome as key modifiers of immune-system aging and discuss a conceptual framework in which age-related changes in immunity might also affect the basic rules by which the immune system operates.

Effect of cryopreservation on viability and growth efficiency of stromal-epithelial cells derived from neonatal human thymus

The thymus is the major site of T lymphocyte generation and so is critical for a functional adaptive immune system. Since, thymectomy is a component of neonatal surgery for congenital heart diseases, it provides great potential for collection and storage of thymic tissue for autologous transplantation. However, specific investigation into the optimum parameters for thymic tissue cryopreservation have not been conducted. In this research, we evaluated the effect of different cryoprotective media compositions, which included penetrating (Me₂SO, glycerol) and non-penetrating (dextran-40, sucrose, hydroxyethyl starch) components, on the viability and functionality of frozen-thawed human thymic samples to select an optimal cryoprotective medium suitable for long-term storage of thymic tissue and a stromal-epithelial enriched population. Our primary focus was on receiving, low-temperature storage, culturing and evaluation of thymic tissue samples from newborns and infants with congenital heart diseases, who had undergone thymectomy as a part of standard surgical procedure. Thus, this work builds the platform for autologous clinical intervention into the thymus-deficient patients with congenital heart diseases. From our data, we conclude that although there were no significant differences in efficiency of tested cryoprotective media compositions, the combination of Me₂SO and dextran-40 compounds was the most suitable for long-term storage both thymic cell suspensions and thymic fragments based on the viability of CD326⁺ epithelial cells and stromal-epithelial cell monolayer formation.

Microbial lysate upregulates host oxytocin

Neuropeptide hormone oxytocin has roles in social bonding, energy metabolism, and wound healing contributing to good physical, mental and social health. It was previously shown that feeding of a human commensal microbe Lactobacillus reuteri (L. reuteri) is sufficient to up-regulate endogenous oxytocin levels and improve wound healing capacity in mice. Here we show that oral L. reuteri-induced skin wound repair benefits extend to human subjects. Further, dietary supplementation with a sterile lysate of this microbe alone is sufficient to boost systemic oxytocin levels and improve wound repair capacity. Oxytocin-producing cells were found to be increased in the caudal paraventricular nucleus [PVN] of the hypothalamus after feeding of a sterile lysed preparation of L. reuteri, coincident with lowered blood levels of stress hormone corticosterone and more rapid epidermal closure, in mouse models. We conclude that microbe viability is not essential for regulating host oxytocin levels. The results suggest that a peptide or metabolite produced by bacteria may modulate host oxytocin secretion for potential public or personalized health goals.

Untargeted metabolomics analysis of adipogenic transformation in OP9-DL1 cells using liquid chromatography-mass spectrometry: Implications for thymic adipogenesis

Adipocyte deposition is a key feature of age-related thymic involution, but the underlying mechanisms responsible for thymic adiposity remain to be elucidated. In the present study, we utilized rosiglitazone, a potent peroxisome proliferator-activated receptor γ agonist, to induce adipogenic differentiation of OP9-DL1 cells, and detected the metabolomics alterations during adipogenic differentiation by using liquid chromatography-mass spectrometry. The obtained metabolites were further processed by multivariate statistical analysis, including principal component analysis, partial least squares discriminant analysis, and orthogonal projection on latent-structures discriminant analysis. As a result, we identified a total of 33 significantly differential metabolites between dimethyl sulphoxide- and rosiglitazone-treated OP9-DL1 cells, which were closely related to the dysregulation of phospholipid metabolism pathway, oxidative stress, and associated amino acid metabolism. Meanwhile, two pathways including glycerophospholipid metabolism and nitrogen metabolism were significantly perturbed (P < 0.05). Collectively, our results may provide some heuristic guidance for addressing the underlying mechanism of thymic adipogenesis, and future studies are warranted to unravel the functions of these altered metabolites in thymic adipogenesis.

Functionally Diverse NK-Like T Cells Are Effectors and Predictors of Successful Aging

The fundamental challenge of aging and long-term survivorship is maintenance of functional independence and compression of morbidity despite a life history of disease. Inasmuch as immunity is a determinant of individual health and fitness, unraveling novel mechanisms of immune homeostasis in late life is of paramount interest. Comparative studies of young and old persons have documented age-related atrophy of the thymus, the contraction of diversity of the T cell receptor (TCR) repertoire, and the intrinsic inefficiency of classical TCR signaling in aged T cells. However, the elderly have highly heterogeneous health phenotypes. Studies of defined populations of persons aged 75 and older have led to the recognition of successful aging, a distinct physiologic construct characterized by high physical and cognitive functioning without measurable disability. Significantly, successful agers have a unique T cell repertoire; namely, the dominance of highly oligoclonal αβT cells expressing a diverse array of receptors normally expressed by NK cells. Despite their properties of cell senescence, these unusual NK-like T cells are functionally active effectors that do not require engagement of their clonotypic TCR. Thus, NK-like T cells represent a beneficial remodeling of the immune repertoire with advancing age, consistent with the concept of immune plasticity. Significantly, certain subsets are predictors of physical/cognitive performance among older adults. Further understanding of the roles of these NK-like T cells to host defense, and how they integrate with other physiologic domains of function are new frontiers for investigation in Aging Biology. Such pursuits will require a research paradigm shift from the usual young-versus-old comparison to the analysis of defined elderly populations. These endeavors may also pave way to age-appropriate, group-targeted immune interventions for the growing elderly population.

Systemic toxoplasma infection triggers a long-term defect in the generation and function of naive T lymphocytes

Kugler et al. show that systemic infection with Toxoplasma gondii triggers a long-term impairment in thymic function, which leads to an immunodeficient state reflected in decreased antimicrobial resistance.

Because antigen-stimulated naive T cells either die as effectors or enter the activated/memory pool, continuous egress of new T lymphocytes from thymus is essential for maintenance of peripheral immune homeostasis. Unexpectedly, we found that systemic infection with the protozoan Toxoplasma gondii triggers not only a transient increase in activated CD4⁺ Th1 cells but also a persistent decrease in the size of the naive CD4⁺ T lymphocyte pool. This immune defect is associated with decreased thymic output and parasite-induced destruction of the thymic epithelium, as well as disruption of the overall architecture of that primary lymphoid organ. Importantly, the resulting quantitative and qualitative deficiency in naive CD4⁺ T cells leads to an immunocompromised state that both promotes chronic toxoplasma infection and leads to decreased resistance to challenge with an unrelated pathogen. These findings reveal that systemic infectious agents, such as T. gondii, can induce long-term immune alterations associated with impaired thymic function. When accumulated during the lifetime of the host, such events, even when occurring at low magnitude, could be a contributing factor in immunological senescence.