Glucocorticoids Drive Diurnal Oscillations in T Cell Distribution and Responses by Inducing Interleukin-7 Receptor and CXCR4

Subclone from CT26 resistant to anti-PD-1 therapy associated with increased expression of genes related to glucocorticoids

BACKGROUND

Although the use of anti-PD-1 antibodies has fundamentally changed traditional cancer treatment, most patients are resistant to anti-PD-1 treatment. Glucocorticoids (GCs) play an important role in tumorigenesis and tumor progression, but the role of endogenous GCs in resistance to anti-PD-1 antibody therapy remains unclear.

METHODS

Single cell-derived cell lines (SCDCLs) were generated from a colorectal cancer cell line (CT26) using limiting dilution. We analyzed tumor tissues from anti-PD-1 antibody-treated and untreated mice inoculated with SCDCLs via transcriptome sequencing and flow cytometry to detect pathway activity and immune cell composition changes in the tumor microenvironment.

RESULTS

Five SCDCLs were inoculated into wild-type BALB/c mice (all tumorigenic). Single-cell clone (SCC)-2 exhibited the slowest growth rates both in vivo and in vitro compared to other single-cell clones, and better long-term survival than SCC1 and CT26. Flow cytometry showed that SCC2 tumor-bearing mice exhibited significantly higher infiltration of T cells within the tumor tissue, and higher expression of PD-1 on these T cells than the other groups in vivo. However, the SCC2 group showed no response to anti-PD-1 therapy. Transcriptome analysis revealed that the SCC2 group exhibited increased expression of genes related to GC (Hsd11b1, Sgk3, Tgfbr2, and Il7r) compared to SCC2-anti-PD-1 treated tumors.

CONCLUSIONS

GC pathway activation is related to resistance to anti-PD-1 therapy.

Role of Neurotransmitters in Steady State Hematopoiesis, Aging, and Leukemia

Haematopoiesis within the bone marrow (BM) represents a complex and dynamic process intricately regulated by neural signaling pathways. This delicate orchestration is susceptible to disruption by factors such as aging, diabetes, and obesity, which can impair the BM niche and consequently affect haematopoiesis. Genetic mutations in Tet2, Dnmt3a, Asxl1, and Jak2 are known to give rise to clonal haematopoiesis of intermediate potential (CHIP), a condition linked to age-related haematological malignancies. Despite these insights, the exact roles of circadian rhythms, sphingosine-1-phosphate (S1P), stromal cell-derived factor-1 (SDF-1), sterile inflammation, and the complement cascade on various BM niche cells remain inadequately understood. Further research is needed to elucidate how BM niche cells contribute to these malignancies through neural regulation and their potential in the development of gene-corrected stem cells. This literature review describes the updated functional aspects of BM niche cells in haematopoiesis within the context of haematological malignancies, with a particular focus on neural signaling and the potential of radiomitigators in acute radiation syndrome. Additionally, it underscores the pressing need for technological advancements in stem cell-based therapies to alleviate the impacts of immunological stressors. Recent studies have illuminated the microheterogeneity and temporal stochasticity of niche cells within the BM during haematopoiesis, emphasizing the updated roles of neural signaling and immunosurveillance. The development of gene-corrected stem cells capable of producing blood, immune cells, and tissue-resident progeny is essential for combating age-related haematological malignancies and overcoming immunological challenges. This review aims to provide a comprehensive overview of these evolving insights and their implications for future therapeutic strategies.

Targeting the intestinal circadian clock by meal timing ameliorates gastrointestinal inflammation

The expression of clock genes has been observed to be impaired in biopsies from patients with inflammatory bowel disease (IBD). Disruption of circadian rhythms, which occurs in shift workers, has been linked to an increased risk of gastrointestinal diseases, including IBD. The peripheral circadian clock in intestinal epithelial cells (IECs) was previously shown to balance gastrointestinal homeostasis by regulating the microbiome. Here, we demonstrated that the intestinal clock is disrupted in an IBD-relevant mouse model (IL-10-/-). A lack of the intestinal clock gene (Bmal1) in intestinal epithelial cells (IECs) in a chemically and a novel genetically induced colitis model (DSS, Bmal1IEC-/-xIL-10-/-) promoted colitis and dramatically reduced survival rates. Germ-free Bmal1IEC-/- mice colonized with disease-associated microbiota from IL-10-/- mice exhibited increased inflammatory responses, highlighting the importance of the local intestinal clock for microbiota-induced IBD development. Targeting the intestinal clock directly by timed restricted feeding (RF) in IL-10-/- mice restored intestinal clock functions, including immune cell recruitment and microbial rhythmicity; improved inflammatory responses; dramatically enhanced survival rates and rescued the histopathological phenotype. In contrast, RF failed to improve IBD symptoms in Bmal1IEC-/-xIL-10-/- mice, demonstrating the significance of the intestinal clock in determining the beneficial effect of RF. Overall, we provide evidence that intestinal clock dysfunction triggers host immune imbalance and promotes the development and progression of IBD-like colitis. Enhancing intestinal clock function by RF modulates the pathogenesis of IBD and thus could become a novel strategy to ameliorate symptoms in IBD patients.

Stress systems exacerbate the inflammatory response after corneal abrasion in sleep-deprived mice via the IL-17 signaling pathway

Sleep deprivation (SD) has a wide range of adverse health effects. However, the mechanisms by which SD influences corneal pathophysiology and its post-wound healing remain unclear. This study aimed to examine the basic physiological characteristics of the cornea in mice subjected to SD and determine the pathophysiological response to injury after corneal abrasion. Using a multi-platform water environment method as an SD model, we found that SD leads to disturbances of corneal proliferative, sensory, and immune homeostasis as well as excessive inflammatory response and delayed repair after corneal abrasion by inducing hyperactivation of the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. Pathophysiological changes in the cornea mainly occurred through the activation of the IL-17 signaling pathway. Blocking both adrenergic and glucocorticoid synthesis and locally neutralizing IL-17A significantly improved corneal homeostasis and the excessive inflammatory response and delay in wound repair following corneal injury in SD-treated mice. These results indicate that optimal sleep quality is essential for the physiological homeostasis of the cornea and its well-established repair process after injury. Additionally, these observations provide potential therapeutic targets to ameliorate SD-induced delays in corneal wound repair by inhibiting or blocking the activation of the stress system and its associated IL-17 signaling pathway.

Glucocorticoids paradoxically promote steroid resistance in B cell acute lymphoblastic leukemia through CXCR4/PLC signaling

Glucocorticoid (GC) resistance in childhood relapsed B-cell acute lymphoblastic leukemia (B-ALL) represents an important challenge. Despite decades of clinical use, the mechanisms underlying resistance remain poorly understood. Here, we report that in B-ALL, GC paradoxically induce their own resistance by activating a phospholipase C (PLC)-mediated cell survival pathway through the chemokine receptor, CXCR4. We identify PLC as aberrantly activated in GC-resistant B-ALL and its inhibition is able to induce cell death by compromising several transcriptional programs. Mechanistically, dexamethasone (Dex) provokes CXCR4 signaling, resulting in the activation of PLC-dependent Ca2+ and protein kinase C signaling pathways, which curtail anticancer activity. Treatment with a CXCR4 antagonist or a PLC inhibitor improves survival of Dex-treated NSG mice in vivo. CXCR4/PLC axis inhibition significantly reverses Dex resistance in B-ALL cell lines (in vitro and in vivo) and cells from Dex resistant ALL patients. Our study identifies how activation of the PLC signalosome in B-ALL by Dex limits the upfront efficacy of this chemotherapeutic agent.

Circadian-clock-controlled endocrine and cytokine signals regulate multipotential innate lymphoid cell progenitors in the bone marrow

Innate lymphoid cells (ILCs), strategically positioned throughout the body, undergo population declines over time. A solution to counteract this problem is timely mobilization of multipotential progenitors from the bone marrow. It remains unknown what triggers the mobilization of bone marrow ILC progenitors (ILCPs). We report that ILCPs are regulated by the circadian clock to emigrate and generate mature ILCs in the periphery. We found that circadian-clock-defective ILCPs fail to normally emigrate and generate ILCs. We identified circadian-clock-controlled endocrine and cytokine cues that, respectively, regulate the retention and emigration of ILCPs at distinct times of each day. Activation of the stress-hormone-sensing glucocorticoid receptor upregulates CXCR4 on ILCPs for their retention in the bone marrow, while the interleukin-18 (IL-18) and RORα signals upregulate S1PR1 on ILCPs for their mobilization to the periphery. Our findings establish important roles of circadian signals for the homeostatic efflux of bone marrow ILCPs.

Circadian tumor infiltration and function of CD8+ T cells dictate immunotherapy efficacy

The quality and quantity of tumor-infiltrating lymphocytes, particularly CD8+ T cells, are important parameters for the control of tumor growth and response to immunotherapy. Here, we show in murine and human cancers that these parameters exhibit circadian oscillations, driven by both the endogenous circadian clock of leukocytes and rhythmic leukocyte infiltration, which depends on the circadian clock of endothelial cells in the tumor microenvironment. To harness these rhythms therapeutically, we demonstrate that efficacy of chimeric antigen receptor T cell therapy and immune checkpoint blockade can be improved by adjusting the time of treatment during the day. Furthermore, time-of-day-dependent T cell signatures in murine tumor models predict overall survival in patients with melanoma and correlate with response to anti-PD-1 therapy. Our data demonstrate the functional significance of circadian dynamics in the tumor microenvironment and suggest the importance of leveraging these features for improving future clinical trial design and patient care.

The temporal expression pattern of classical MHC class I in sleep-restricted mice: Generalizations and broader implications

The intricate relationship between sleep and leukocyte trafficking has garnered intense attention, particularly their homing dynamics to secondary lymphoid organs under normal and restricted sleep (SR). Considering the scarcity of information regarding circadian rhythms in major histocompatibility class I (MHC-I) expression in SR, we designed a study that assessed the temporal expression of MHC-I in murine lymph nodes and spleen and the subsequent effects of sleep recovery. Male C57BL/6, housed in 12:12 light/dark cycle, were grouped into control (C) and SR. SR was carried for one week before lymphoid tissues were sampled at selected time points and assessed for leukocyte number and MHC-I expression. SR resulted in 21% decrease in granulocyte and 24% increase in agranulocyte numbers. In C, MHC-I expression pattern in lymph nodes was bimodal and relatively higher than splenocytes during the animal's active phase (110.2 ± 1.8 vs 81.9 ± 3.8, respectively; p = 0.002). Splenocytes; however, showed a bimodal pattern upon SR, with higher protein levels during the rest than the activity period (154.6 + 36.2 vs 99.5 + 15.9, respectively; p = 0.002), suggesting preparedness for a potential infection. Furthermore, SR caused a significant drop in MHC-I expression at the onset of rest with 57% and 30% reduction in lymph nodes and splenocytes, respectively. However, the overall protein expression collectively taken from both lymphoid tissues remained stable, emphasizing its indispensable role in immunological homeostasis. This stability coincided with the restoration of protein levels to baseline after a short sleep recovery period, resembling a reset for MHC-I antigen presentation following a week of SR. Understanding the interplay between MHC-I expression and contextual factors could enhance treatment protocols, refining the efficacy and time precision of glucocorticoid-based therapies in immune modulation.

Circadian rhythm regulates the function of immune cells and participates in the development of tumors

Circadian rhythms are present in almost all cells and play a crucial role in regulating various biological processes. Maintaining a stable circadian rhythm is essential for overall health. Disruption of this rhythm can alter the expression of clock genes and cancer-related genes, and affect many metabolic pathways and factors, thereby affecting the function of the immune system and contributing to the occurrence and progression of tumors. This paper aims to elucidate the regulatory effects of BMAL1, clock and other clock genes on immune cells, and reveal the molecular mechanism of circadian rhythm's involvement in tumor and its microenvironment regulation. A deeper understanding of circadian rhythms has the potential to provide new strategies for the treatment of cancer and other immune-related diseases.

Circadian rhythm regulation in the immune system

Circadian rhythms are a ubiquitous feature in nearly all living organisms, representing oscillatory patterns with a 24-h cycle that are widespread across various physiological processes. Circadian rhythms regulate a multitude of physiological systems, including the immune system. At the molecular level, most immune cells autonomously express clock-regulating genes, which play critical roles in regulating immune cell functions. These functions encompass migration, phagocytic activity, immune cell metabolism (such as mitochondrial structural function and metabolism), signalling pathway activation, inflammatory responses, innate immune recognition, and adaptive immune processes (including vaccine responses and pathogen clearance). The endogenous circadian clock orchestrates multifaceted rhythmicity within the immune system, optimizing immune surveillance and responsiveness; this bears significant implications for maintaining immune homeostasis and resilience against diseases. This work provides an overview of circadian rhythm regulation within the immune system.

The β2-adrenergic receptor (ADRB2) entrains circadian gene oscillation and diurnal responses to virus infection in CD8 + T cells

Adaptive immune cells are regulated by circadian rhythms (CR) under both steady state conditions and during responses to infection. Cytolytic CD8 + T cells display variable responses to infection depending upon the time of day of exposure. However, the neuronal signals that entrain these cyclic behaviors remain unknown. Immune cells express a variety of neurotransmitter receptors including nicotinic, glucocorticoid, and adrenergic receptors. Here, we demonstrate that the β2-adrenergic receptor (ADRB2) regulates the periodic oscillation of select core clock genes, such as Per2 and Bmal1 , and selective loss of the Adrb2 gene dramatically perturbs the normal diurnal oscillation of clock gene expression in CD8 + T cells. Consequently, their circadian-regulated anti-viral response is dysregulated, and the diurnal development of CD8 + T cells into variegated populations of cytolytic T cell (CTL) effectors is dramatically altered in the absence of ADRB2 signaling. Thus, the Adrb2 directly entrains core clock gene oscillation and regulates CR-dependent T cell responses to virus infection as a function of time-of-day of pathogen exposure.

One Sentence Summary

The β2-adrenergic receptor regulates circadian gene oscillation and downstream daily timing of cytolytic T cell responses to virus infection.

Caloric restriction for the immunometabolic control of human health

Nutrition affects all physiological processes occurring in our body, including those related to the function of the immune system; indeed, metabolism has been closely associated with the differentiation and activity of both innate and adaptive immune cells. While excessive energy intake and adiposity have been demonstrated to cause systemic inflammation, several clinical and experimental evidence show that calorie restriction (CR), not leading to malnutrition, is able to delay aging and exert potent anti-inflammatory effects in different pathological conditions. This review provides an overview of the ability of different CR-related nutritional strategies to control autoimmune, cardiovascular, and infectious diseases, as tested by preclinical studies and human clinical trials, with a specific focus on the immunological aspects of these interventions. In particular, we recapitulate the state of the art on the cellular and molecular mechanisms pertaining to immune cell metabolic rewiring, regulatory T cell expansion, and gut microbiota composition, which possibly underline the beneficial effects of CR. Although studies are still needed to fully evaluate the feasibility and efficacy of the nutritional intervention in clinical practice, the experimental observations discussed here suggest a relevant role of CR in lowering the inflammatory state in a plethora of different pathologies, thus representing a promising therapeutic strategy for the control of human health.

Chronic Inflammation Disrupts Circadian Rhythms in Splenic CD4+ and CD8+ T Cells in Mice

Internal circadian clocks coordinate 24 h rhythms in behavior and physiology. Many immune functions show daily oscillations, and cellular circadian clocks can impact immune functions and disease outcome. Inflammation may disrupt circadian clocks in peripheral tissues and innate immune cells. However, it remains elusive if chronic inflammation impacts adaptive immune cell clock, e.g., in CD4+ and CD8+ T lymphocytes. We studied this in the experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis, as an established experimental paradigm for chronic inflammation. We analyzed splenic T cell circadian clock and immune gene expression rhythms in mice with late-stage EAE, CFA/PTx-treated, and untreated mice. In both treatment groups, clock gene expression rhythms were altered with differential effects for baseline expression and peak phase compared with control mice. Most immune cell marker genes tested in this study did not show circadian oscillations in either of the three groups, but time-of-day- independent alterations were observed in EAE and CFA/PTx compared to control mice. Notably, T cell effects were likely independent of central clock function as circadian behavioral rhythms in EAE mice remained intact. Together, chronic inflammation induced by CFA/PTx treatment and EAE immunization has lasting effects on circadian rhythms in peripheral immune cells.

Local Effects of Steroid Hormones within the Bone Microenvironment

Steroid hormone production via the adrenal cortex, gonads, and placenta (so-called glandular steroidogenesis) is responsible for the endocrine control of the body's homeostasis and is organized by a feedback regulatory mechanism based on the hypothalamus-pituitary-steroidogenic gland axis. On the other hand, recently discovered extraglandular steroidogenesis occurring locally in different tissues is instead linked to paracrine or autocrine signaling, and it is independent of the control by the hypothalamus and pituitary glands. Bone cells, such as bone-forming osteoblasts, osteoblast-derived osteocytes, and bone-resorbing osteoclasts, respond to steroid hormones produced by both glandular and extraglandular steroidogenesis. Recently, new techniques to identify steroid hormones, as well as synthetic steroids and steroidogenesis inhibitors, have been introduced, which greatly empowered steroid hormone research. Based on recent literature and new advances in the field, here we review the local role of steroid hormones in regulating bone homeostasis and skeletal lesion formation. The novel idea of extraglandular steroidogenesis occurring within the skeletal system raises the possibility of the development of new therapies for the treatment of bone diseases.

Microbiota configuration determines nutritional immune optimization

Mild or transient dietary restriction (DR) improves many aspects of health and aging. Emerging evidence from us and others has demonstrated that DR also optimizes the development and quality of immune responses. However, the factors and mechanisms involved remain to be elucidated. Here, we propose that DR-induced optimization of immunological memory requires a complex cascade of events involving memory T cells, the intestinal microbiota, and myeloid cells. Our findings suggest that DR enhances the ability of memory T cells to recruit and activate myeloid cells in the context of a secondary infection. Concomitantly, DR promotes the expansion of commensal Bifidobacteria within the large intestine, which produce the short-chain fatty acid acetate. Acetate conditioning of the myeloid compartment during DR enhances the capacity of these cells to kill pathogens. Enhanced host protection during DR is compromised when Bifidobacteria expansion is prevented, indicating that microbiota configuration and function play an important role in determining immune responsiveness to this dietary intervention. Altogether, our study supports the idea that DR induces both memory T cells and the gut microbiota to produce distinct factors that converge on myeloid cells to promote optimal pathogen control. These findings suggest that nutritional cues can promote adaptation and co-operation between multiple immune cells and the gut microbiota, which synergize to optimize immunity and protect the collective metaorganism.

Splenic stromal niches in homeostasis and immunity

The spleen is a gatekeeper of systemic immunity where immune responses against blood-borne pathogens are initiated and sustained. Non-haematopoietic stromal cells construct microanatomical niches in the spleen that make diverse contributions to physiological spleen functions and regulate the homeostasis of immune cells. Additional signals from spleen autonomic nerves also modify immune responses. Recent insight into the diversity of the splenic fibroblastic stromal cells has revised our understanding of how these cells help to orchestrate splenic responses to infection and contribute to immune responses. In this Review, we examine our current understanding of how stromal niches and neuroimmune circuits direct the immunological functions of the spleen, with a focus on T cell immunity.

Acute and Repeated Ozone Exposures Differentially Affect Circadian Clock Gene Expression in Mice

Circadian rhythms have an established role in regulating physiological processes, such as inflammation, immunity, and metabolism. Ozone, a common environmental pollutant with strong oxidative potential, is implicated in lung inflammation/injury in asthmatics. However, whether O3 exposure affects the expression of circadian clock genes in the lungs is not known. In this study, changes in the expression of core clock genes are analyzed in the lungs of adult female and male mice exposed to filtered air (FA) or O3 using qRT-PCR. The findings are confirmed using an existing RNA-sequencing dataset from repeated FA- and O3 -exposed mouse lungs and validated by qRT-PCR. Acute O3 exposure significantly alters the expression of clock genes in the lungs of females (Per1, Cry1, and Rora) and males (Per1). RNA-seq data revealing sex-based differences in clock gene expression in the airway of males (decreased Nr1d1/Rev-erbα) and females (increased Skp1), parenchyma of females and males (decreased Nr1d1 and Fbxl3 and increased Bhlhe40 and Skp1), and alveolar macrophages of males (decreased Arntl/Bmal1, Per1, Per2, Prkab1, and Prkab2) and females (increased Cry2, Per1, Per2, Csnk1d, Csnk1e, Prkab2, and Fbxl3). These findings suggest that lung inflammation caused by O3 exposure affects clock genes which may regulate key signaling pathways.

Stress regulates Alzheimer's disease progression via selective enrichment of CD8+ T cells

This study investigates stress's impact on Alzheimer's disease (AD) using male APP/PS1 transgenic mice. Negative stressors (chronic social defeat, restraint) and positive hedonia (environmental enrichment, EE) were applied. Stress worsens AD pathology, while EE slows progression. Brain RNA sequencing reveals interleukin-6 (IL-6) and IL-10 as key stress-related AD regulators. Flow cytometry shows that the CD8+/CD4+ T cell ratio shifts in response to stress exposure and EE. Stress exposure increases CD8+/CD4+ ratio, opposite to EE. Depletion and enrichment of CD8+ T cells both accelerate AD, indicating immune intervention's negative impact. Stress management and balanced immunity may aid AD therapy, highlighting novel potential treatment.

Molecular components of the circadian clock regulate HIV-1 replication

Human immunodeficiency virus 1 (HIV-1) causes major health burdens worldwide and still lacks curative therapies and vaccines. Circadian rhythms are endogenous daily oscillations that coordinate an organism's response to its environment and invading pathogens. Peripheral viral loads of HIV-1 infected patients show diurnal variation; however, the underlying mechanisms remain unknown. Here, we demonstrate a role for the cell-intrinsic clock to regulate rhythmic HIV-1 replication in circadian-synchronized systems. Silencing the circadian activator Bmal1 abolishes this phenotype, and we observe BMAL1 binding to the HIV-1 promoter. Importantly, we show differential binding of the nuclear receptors REV-ERB and ROR to the HIV-long terminal repeat at different circadian times, demonstrating a dynamic interplay in time-of-day regulation of HIV-1 transcription. Bioinformatic analysis shows circadian regulation of host factors that control HIV-1 replication, providing an additional mechanism for rhythmic viral replication. This study increases our understanding of the circadian regulation of HIV-1, which can ultimately inform new therapies.

Immunological and inflammatory effects of infectious diseases in circadian rhythm disruption and future therapeutic directions

BACKGROUND

Circadian rhythm is characterised by daily variations in biological activity to align with the light and dark cycle. These diurnal variations, in turn, influence physiological functions such as blood pressure, temperature, and sleep-wake cycle. Though it is well established that the circadian pathway is linked to pro-inflammatory responses and circulating immune cells, its association with infectious diseases is widely unknown.

OBJECTIVE

This comprehensive review aims to describe the association between circadian rhythm and host immune response to various kinds of infection.

METHODS

We conducted a literature search in databases Pubmed/Medline and Science direct. Our paper includes a comprehensive analysis of findings from articles in English which was related to our hypothesis.

FINDINGS

Molecular clocks determine circadian rhythm disruption in response to infection, influencing the host's response toward infection. Moreover, there is a complex interplay with intrinsic oscillators of pathogens and the influence of specific infectious processes on the CLOCK: BMAL1 pathway. Such mechanisms vary for bacterial and viral infections, both well studied in the literature. However, less is known about the association of parasitic infections and fungal pathogens with circadian rhythm modulation.

CONCLUSION

It is shown that bidirectional relationships exist between circadian rhythm disruption and infectious process, which contains interplay between the host's and pathogens' circadian oscillator, immune response, and the influence of specific infectious. Further studies exploring the modulations of circadian rhythm and immunity can offer novel explanations of different susceptibilities to infection and can lead to therapeutic avenues in circadian immune modulation of infectious diseases.

Regulation of Cytotoxic CD8+ T Cells by the Circadian Clock

Most aspects of physiology, including immunity, present 24-h variations called circadian rhythms. In this review, we examine the literature on the circadian regulation of CD8+ T cells, which are important to fight intracellular infections and tumors. CD8+ T cells express circadian clock genes, and ∼6% of their transcriptome presents circadian oscillations. CD8+ T cell counts present 24-h rhythms in the blood and in secondary lymphoid organs, which depend on the clock in these cells as well as on hormonal rhythms. Moreover, the strength of the response of these cells to Ag presentation varies according to time of day, a rhythm dependent on the CD8+ T cell clock. The relevance of CD8+ T cell circadian rhythms is shown by the daily variations in the fight of intracellular infections. Such a circadian regulation also has implications for cancer, as well as the optimization of vaccination and immunotherapy.

The interplay between circadian clock and viral infections: A molecular perspective

The circadian clock influences almost every aspect of mammalian behavioral, physiological and metabolic processes. Being a hierarchical network, the circadian clock is driven by the central clock in the brain and is composed of several peripheral tissue-specific clocks. It orchestrates and synchronizes the daily oscillations of biological processes to the environment. Several pathological events are influenced by time and seasonal variations and as such implicate the clock in pathogenesis mechanisms. In context with viral infections, circadian rhythmicity is closely associated with host susceptibility, disease severity, and pharmacokinetics and efficacies of antivirals and vaccines. Leveraging the circadian molecular mechanism insights has increased our understanding of clock infection biology and proposes new avenues for viral diagnostics and therapeutics. In this chapter, we address the molecular interplay between the circadian clock and viral infections and discuss the importance of chronotherapy as a complementary approach to conventional medicines, emphasizing the significance of virus-clock studies.

Nanoenzyme engineered neutrophil-derived exosomes attenuate joint injury in advanced rheumatoid arthritis via regulating inflammatory environment

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovitis and destruction of cartilage, promoted by sustained inflammation. However, current treatments remain unsatisfactory due to lacking of selective and effective strategies for alleviating inflammatory environments in RA joint. Inspired by neutrophil chemotaxis for inflammatory region, we therefore developed neutrophil-derived exosomes functionalized with sub-5 nm ultrasmall Prussian blue nanoparticles (uPB-Exo) via click chemistry, inheriting neutrophil-targeted biological molecules and owning excellent anti-inflammatory properties. uPB-Exo can selectively accumulate in activated fibroblast-like synoviocytes, subsequently neutralizing pro-inflammatory factors, scavenging reactive oxygen species, and alleviating inflammatory stress. In addition, uPB-Exo effectively targeted to inflammatory synovitis, penetrated deeply into the cartilage and real-time visualized inflamed joint through MRI system, leading to precise diagnosis of RA in vivo with high sensitivity and specificity. Particularly, uPB-Exo induced a cascade of anti-inflammatory events via Th17/Treg cell balance regulation, thereby significantly ameliorating joint damage. Therefore, nanoenzyme functionalized exosomes hold the great potential for enhanced treatment of RA in clinic.

•

uPB-Exo were firstly developed by combining NE-Exo with sub-5 nm ultrasmall PB nanoparticles via click chemistry.

•

uPB-Exo selectively targeted inflamed joints via neutrophil-targeted biological molecules inherited from neutrophils.

•

uPB-Exo accumulated in active FLS, and eventually scavenged reactive oxygen species and alleviated inflammatory stress.

•

uPB-Exo induced a cascade of anti-inflammatory events via Th17/Treg cell balance regulation, thereby significantly ameliorating joint damage.

•

uPB-Exo, as a drug free therapeutical agent, holds the great potential for enhanced treatment of RA in clinic.

Time of Day of Vaccination Does Not Associate With SARS-CoV-2 Antibody Titer Following First Dose of mRNA COVID-19 Vaccine

The immune system exhibits circadian rhythms, and its response to viral infection is influenced by the circadian clock system. Previous studies have reported associations between the time of day of vaccination against COVID-19 and production of anti-SARS-CoV-2 antibody titer. We examined the effect of vaccination time of day on anti-SARS-CoV-2 antibody titer after the first dose of vaccination with the mRNA-1273 (Moderna) COVID-19 vaccine in an adult population. A total of 332 Japanese adults participated in the present study. All participants were not infected with SARS-CoV-2 and had already received the first dose of mRNA-1273 2 to 4 weeks prior to participating in the study. The participants were asked to provide basic demographic characteristics (age, sex, medical history, allergy, medication, and mean sleep duration), the number of days after the first dose of vaccination, and the time of day of vaccination. Blood was collected from the participants, and SARS-CoV-2 antibody titers were measured. Ordinary least square regression was used for assessing the relationship between basic demographic characteristics, number of days after vaccination, time of day of vaccination, and the log₁₀-transformed normalized antibody titer. The least square mean of antibody titers was not associated with the vaccination time and sleep durations. The least square means of antibody titers was associated with age; the antibody titers decreased in people aged 50 to 59 years and 60 to 64 years. The present findings demonstrate that the vaccination time with mRNA-1273 was not associated with the SARS-CoV-2 antibody titer in an adult population, suggesting that these results do not support restricting vaccination to a particular time of day. The present findings may be useful in optimizing SARS-CoV-2 vaccination strategies.

Circadian rhythms in psoriasis and the potential of chronotherapy in psoriasis management

The physiology and pathology of the skin are influenced by daily oscillations driven by a master clock located in the brain, and peripheral clocks in individual cells. The pathogenesis of psoriasis is circadian-rhythmic, with flares of disease and symptoms such as itch typically being worse in the evening/night-time. Patients with psoriasis have changes in circadian oscillations of blood pressure and heart rate, supporting wider circadian disruption. In addition, shift work, a circadian misalignment challenge, is associated with psoriasis. These features may be due to underlying circadian control of key effector elements known to be relevant in psoriasis such as cell cycle, proliferation, apoptosis and inflammation. Indeed, peripheral clock pathology may lead to hyperproliferation of keratinocytes in the basal layers, insufficient apoptosis of differentiating keratinocytes in psoriatic epidermis, dysregulation of skin-resident and migratory immune cells and modulation of angiogenesis through circadian oscillation of vascular endothelial growth factor A (VEGF-A) in epidermal keratinocytes. Chronotherapeutic effects of topical steroids and topical vitamin D analogues have been reported, suggesting that knowledge of circadian phase may improve the efficacy, and therapeutic index of treatments for psoriasis. In this viewpoint essay, we review the current literature on circadian disruption in psoriasis. We explore the hypothesis that psoriasis is circadian-driven. We also suggest that investigation of the circadian components specific to psoriasis and that the in vitro investigation of circadian regulation of psoriasis will contribute to the development of a novel chronotherapeutic treatment strategy for personalised psoriasis management. We also propose that circadian oscillations of VEGF-A offer an opportunity to enhance the efficacy and tolerability of a novel anti-VEGF-A therapeutic approach, through the timed delivery of anti-VEGF-A drugs.

The multisensory regulation of unconventional T cell homeostasis

Unconventional T cells typically group γδ T cells, invariant Natural Killer T cells (NKT) and Mucosal Associated Invariant T (MAIT) cells. With their pre-activated status and biased tropism for non-lymphoid organs, they provide a rapid (innate-like) and efficient first line of defense against pathogens at strategical barrier sites, while they can also trigger chronic inflammation, and unexpectedly contribute to steady state physiology. Thus, a tight control of their homeostasis is critical to maintain tissue integrity. In this review, we discuss the recent advances of our understanding of the factors, from neuroimmune to inflammatory regulators, shaping the size and functional properties of unconventional T cell subsets in non-lymphoid organs. We present a general overview of the mechanisms common to these populations, while also acknowledging specific aspects of their diversity. We mainly focus on their maintenance at steady state and upon inflammation, highlighting some key unresolved issues and raising upcoming technical, fundamental and translational challenges.

Developmental Programming by Perinatal Glucocorticoids

Early-life environmental factors can have persistent effects on physiological functions by altering developmental procedures in various organisms. Recent experimental and epidemiological studies now further support the idea that developmental programming is also present in mammals, including humans, influencing long-term health. Although the mechanism of programming is still largely under investigation, the role of endocrine glucocorticoids in developmental programming is gaining interest. Studies found that perinatal glucocorticoids have a persistent effect on multiple functions of the body, including metabolic, behavioral, and immune functions, in adulthood. Several mechanisms have been proposed to play a role in long-term programming. In this review, recent findings on this topic are summarized and the potential biological rationale behind this phenomenon is discussed.

Tregs in visceral adipose tissue up-regulate circadian-clock expression to promote fitness and enforce a diurnal rhythm of lipolysis

Regulatory T cells (T_regs) in nonlymphoid organs provide critical brakes on inflammation and regulate tissue homeostasis. Although so-called "tissue T_regs" are phenotypically and functionally diverse, serving to optimize their performance and survival, up-regulation of pathways related to circadian rhythms is a feature they share. Yet the diurnal regulation of T_regs and its consequences are controversial and poorly understood. Here, we profiled diurnal variations in visceral adipose tissue (VAT) and splenic T_regs in the presence and absence of core-clock genes. VAT, but not splenic, T_regs up-regulated their cell-intrinsic circadian program and exhibited diurnal variations in their activation and metabolic state. BMAL1 deficiency specifically in T_regs led to constitutive activation and poor oxidative metabolism in VAT, but not splenic, T_regs. Disruption of core-clock components resulted in loss of fitness: BMAL1-deficient VAT T_regs were preferentially lost during competitive transfers and in heterozygous T_reg^Bmal1Δ females. After 16 weeks of high-fat diet feeding, VAT inflammation was increased in mice harboring BMAL1-deficient T_regs, and the remaining cells lost the transcriptomic signature of bona fide VAT T_regs. Unexpectedly, VAT T_regs suppressed adipocyte lipolysis, and BMAL1 deficiency specifically in T_regs abrogated the characteristic diurnal variation in adipose tissue lipolysis, resulting in enhanced suppression of lipolysis throughout the day. These findings argue for the importance of the cell-intrinsic clock program in optimizing VAT T_reg function and fitness.

High-progesterone environment preserves T cell competency by evading glucocorticoid effects on immune regulation

Progesterone (P4) and glucocorticoid (GC) play crucial roles in the immunoregulation of a mother to accept and maintain a semi-allogenic fetus. P4 concentration increases during pregnancy and becomes much higher in the placenta than in the other peripheral tissues, wherein the concentration of cortisol (COR), the most abundant GC and a strong immunosuppressor, remains uniform throughout the rest of the body. Here, we evaluated the effect of a high-P4 environment on pregnant immunity by comparing it with COR. Naïve T cell proportion increased transiently in peripheral blood of pregnant women just after delivery and decreased after one month. T cells stimulated with superantigen toxic-shock-syndrome-1 (TSST-1) in the presence of P4 stayed in the naïve state and did not increase, irrespective of the presence of COR, and reactive T cells could not survive. Treatment of T cells with P4 without T cell receptor (TCR) stimulation transiently suppressed T cell activation and proliferation, whereas the levels remain unaltered if P4 was not given before stimulation. Comparison of the engraftment and response against specific antigens using hu-PBL-NOG-hIL-4-Tg mice showed that P4-pretreated lymphocytes preserved CD62L expression and engrafted effectively in the spleen. Moreover, they produced antigen-specific antibodies, whereas COR-pretreated lymphocytes did not. These results suggest that a high-P4 environment suppresses T cell activation and induces T cell migration into lymphoid tissues, where they maintain the ability to produce anti-pathogen antibodies, whereas COR does not preserve T cell function. The mechanism may be pivotal in maintaining non-fetus-specific T cell function in pregnancy.

Androgens Alleviate Allergic Airway Inflammation by Suppressing Cytokine Production in Th2 Cells

Asthma is more common in females than males after adolescence. However, the mechanism of the sex bias in the prevalence of asthma remains unknown. To test whether sex steroid hormones have some roles in T cells during development of asthma, we analyzed airway inflammation in T cell–specific androgen receptor (AR)– and estrogen receptor (ER)–deficient mice. T cell–specific AR-deficient male mice developed severer house dust mite–induced allergic airway inflammation than did control male mice, whereas T cell–specific ERα- and ERβ-deficient female mice exhibited a similar degree of inflammation as for control female mice. Furthermore, administration of dihydrotestosterone reduced cytokine production of Th2 cells from control, but not AR-deficient, naive T cells. Transfer of OT-II transgenic AR-deficient Th2 cells into wild-type mice induced severer allergic airway inflammation by OVA than transfer of control Th2 cells. Gene expression profiling suggested that the expression of genes related with cell cycle and Th2 differentiation was elevated in AR-deficient Th2 cells, whereas expression of dual specificity phosphatase (DUSP)-2, a negative regulator of p38, was downregulated. In addition, a chromatin immunoprecipitation assay suggested that AR bound to an AR motif in the 5′ untranslated region of the Dusp2 gene in Th2 cells. Furthermore, the Dusp2 promoter with a wild-type AR motif, but not a mutated motif, was transactivated by dihydrotestosterone in a reporter assay. Finally, forced expression of DUSP-2 by retrovirus vector reduced IL-4 expression in Th2 cells. Thus, these results suggest that androgen signaling suppresses cytokine production of Th2 cells by inducing DUSP-2, explaining, in part, the sex bias of asthma after adolescence.

Induction of natural IgE by glucocorticoids

IgE mediates allergic responses by coating mast cell or basophil surfaces and inducing degranulation upon binding a specific allergen. IgE can also be spontaneously produced in the absence of foreign allergens; yet the origin, regulation, and functions of such "natural" IgE still remain largely unknown. Here, we find that glucocorticoids enhance the production of IgE in B cells both in vivo and ex vivo without antigenic challenge. Such IgE production is promoted by B cell-intrinsic glucocorticoid receptor signaling that reinforces CD40 signaling and synergizes with the IL-4/STAT6 pathway. In addition, we found that rare B cells in the mesenteric lymph nodes are responsible for the production of glucocorticoid-inducible IgE. Furthermore, locally produced glucocorticoids in the gut may induce natural IgE during perturbations of gut homeostasis, such as dysbiosis. Notably, mice preemptively treated with glucocorticoids were protected from subsequent pathogenic anaphylaxis. Together, our results suggest that glucocorticoids, classically considered to be broadly immunosuppressive, have a selective immunostimulatory role in B cells.

Control of Immunity and Allergy by Steroid Hormones

Steroid hormones, especially glucocorticoids, androgens, and estrogens, have profound influence on immunity. Recent studies using cell-type specific steroid hormone receptor-deficient mice have revealed the precise roles of some of these hormones in the immune system. Glucocorticoids are known to have strong anti-inflammatory and immunosuppressive effects and pleiotropic effects on innate and adaptive immune responses. They suppress the production of inflammatory cytokines by macrophages and DCs and the production of IFN-γ by NK cells, thus inhibiting innate immunity. By contrast, glucocorticoids enhance the immune response by inducing the expression of IL-7R and CXCR4 in T cells and the accumulation of T cells in lymphoid organs in accordance with the diurnal change of the glucocorticoid concentration. Thus, glucocorticoids suppress innate immunity but enhance adaptive immunity. Androgens suppress the homeostasis and activation of ILC2s and the differentiation of Th2 and Th17 cells and enhance the suppressive function of Tregs, thereby alleviating allergic airway inflammation. Thus, these steroid hormones have pleiotropic functions in the immune system. Further investigations are awaited on the regulation of immunity and allergy by estrogens using cell-specific steroid hormone receptor-deficient mice.

Control of lymph node activity by direct local innervation

The nervous system detects environmental and internal stimuli and relays this information to immune cells via neurotransmitters and neuropeptides. This is essential to respond appropriately to immunogenic threats and to support system homeostasis. Lymph nodes (LNs) act as sentinels where adaptive immune responses are generated. They are richly innervated by peripheral sympathetic and sensory nerves, which are responsible for the local secretion of neurotransmitters by sympathetic fibers, such as norepinephrine, and neuropeptides by sensory fibers, including calcitonin gene-related peptide (CGRP) and substance P. Additionally, time-of-day-dependent oscillations in nerve activity are associated with differential immune responses, suggesting a potential role for neuroimmune interactions in coordinating immunity in a circadian fashion. Here, we discuss how LN activity is controlled by local innervation.

Cell-Specific Immune Regulation by Glucocorticoids in Murine Models of Infection and Inflammation

Glucocorticoids (GC) are highly potent negative regulators of immune and inflammatory responses. Effects of GC are primarily mediated by the glucocorticoid receptor (GR) which is expressed by all cell types of the immune system. It is, therefore, difficult to elucidate how endogenous GC mediate their effects on immune responses that involve multiple cellular interactions between various immune cell subsets. This review focuses on endogenous GC targeting specific cells of the immune system in various animal models of infection and inflammation. Without the timed release of these hormones, animals infected with various microbes or challenged in inflammatory disease models succumb as a consequence of overshooting immune and inflammatory responses. A clearer picture is emerging that endogenous GC thereby act in a cell-specific and disease model-dependent manner, justifying the need to develop techniques that target GC to individual immune cell types for improved clinical application.

Glucocorticoid signaling and regulatory T cells cooperate to maintain the hair-follicle stem-cell niche

Maintenance of tissue homeostasis is dependent on the communication between stem cells and supporting cells in the same niche. Regulatory T cells (Treg cells) are emerging as a critical component of the stem-cell niche for supporting their differentiation. How Treg cells sense dynamic signals in this microenvironment and communicate with stem cells is mostly unknown. In the present study, by using hair follicles (HFs) to study Treg cell-stem cell crosstalk, we show an unrecognized function of the steroid hormone glucocorticoid in instructing skin-resident Treg cells to facilitate HF stem-cell (HFSC) activation and HF regeneration. Ablation of the glucocorticoid receptor (GR) in Treg cells blocks hair regeneration without affecting immune homeostasis. Mechanistically, GR and Foxp3 cooperate in Treg cells to induce transforming growth factor β3 (TGF-β3), which activates Smad2/3 in HFSCs and facilitates HFSC proliferation. The present study identifies crosstalk between Treg cells and HFSCs mediated by the GR-TGF-β3 axis, highlighting a possible means of manipulating Treg cells to support tissue regeneration.

Brain motor and fear circuits regulate leukocytes during acute stress

The nervous and immune systems are intricately linked¹. Although psychological stress is known to modulate immune function, mechanistic pathways linking stress networks in the brain to peripheral leukocytes remain poorly understood². Here we show that distinct brain regions shape leukocyte distribution and function throughout the body during acute stress in mice. Using optogenetics and chemogenetics, we demonstrate that motor circuits induce rapid neutrophil mobilization from the bone marrow to peripheral tissues through skeletal-muscle-derived neutrophil-attracting chemokines. Conversely, the paraventricular hypothalamus controls monocyte and lymphocyte egress from secondary lymphoid organs and blood to the bone marrow through direct, cell-intrinsic glucocorticoid signalling. These stress-induced, counter-directional, population-wide leukocyte shifts are associated with altered disease susceptibility. On the one hand, acute stress changes innate immunity by reprogramming neutrophils and directing their recruitment to sites of injury. On the other hand, corticotropin-releasing hormone neuron-mediated leukocyte shifts protect against the acquisition of autoimmunity, but impair immunity to SARS-CoV-2 and influenza infection. Collectively, these data show that distinct brain regions differentially and rapidly tailor the leukocyte landscape during psychological stress, therefore calibrating the ability of the immune system to respond to physical threats.

The circadian immune system

The immune system is highly time-of-day dependent. Pioneering studies in the 1960s were the first to identify immune responses to be under a circadian control. Only in the last decade, however, have the molecular factors governing circadian immune rhythms been identified. These studies have revealed a highly complex picture of the interconnectivity of rhythmicity within immune cells with that of their environment. Here, we provide a global overview of the circadian immune system, focusing on recent advances in the rapidly expanding field of circadian immunology.

Targeting Nuclear Receptors for TH17-Mediated Inflammation: REV-ERBerations of Circadian Rhythm and Metabolism

Since their discovery, a significant amount of progress has been made understanding T helper 17 (T_H17) cells' roles in immune homeostasis and disease. Outside of classical cytokine signaling, environmental and cellular intrinsic factors, including metabolism, have proven to be critical for non-pathogenic vs pathogenic T_H17 cell development, clearance of infections, and disease. The nuclear receptor RORγt has been identified as a key regulator of T_H17-mediated inflammation. Nuclear receptors regulate a variety of physiological processes, ranging from reproduction to the circadian rhythm, immunity to metabolism. Outside of RORγt, the roles of other nuclear receptors in T_H17-mediated immunity are not as well established. In this mini-review we describe recent studies that revealed a role for a different member of the nuclear receptor superfamily, REV-ERBα, in the regulation of T_H17 cells and autoimmunity. We highlight similarities and differences between reports, potential roles beyond T_H17-mediated cytokine regulation, unresolved questions in the field, as well as the translational potential of targeting REV-ERBα.

Neural control of immune cell trafficking

Leukocyte trafficking between blood and tissues is an essential function of the immune system that facilitates humoral and cellular immune responses. Within tissues, leukocytes perform surveillance and effector functions via cell motility and migration toward sites of tissue damage, infection, or inflammation. Neurotransmitters that are produced by the nervous system influence leukocyte trafficking around the body and the interstitial migration of immune cells in tissues. Neural regulation of leukocyte dynamics is influenced by circadian rhythms and altered by stress and disease. This review examines current knowledge of neuro–immune interactions that regulate leukocyte migration and consequences for protective immunity against infections and cancer.

Adaptive immunity, chronic inflammation and the clock

The adaptive arm of the immune system facilitates recognition of specific foreign pathogens and, via the action of T and B lymphocytes, induces a fine-tuned response to target the pathogen and develop immunological memory. The functionality of the adaptive immune system exhibits daily 24-h variation both in homeostatic processes (such as lymphocyte trafficking and development of T lymphocyte subsets) and in responses to challenge. Here, we discuss how the circadian clock exerts influence over the function of the adaptive immune system, considering the roles of cell intrinsic clockwork machinery and cell extrinsic rhythmic signals. Inappropriate or misguided actions of the adaptive immune system can lead to development of autoimmune diseases such as rheumatoid arthritis, ulcerative colitis and multiple sclerosis. Growing evidence indicates that disturbance of the circadian clock has negative impact on development and progression of these chronic inflammatory diseases and we examine current understanding of clock-immune interactions in the setting of these inflammatory conditions. A greater appreciation of circadian control of adaptive immunity will facilitate further understanding of mechanisms driving daily variation in disease states and drive improvements in the diagnosis and treatment of chronic inflammatory diseases.

Macrophage Meets the Circadian Clock: Implication of the Circadian Clock in the Role of Macrophages in Acute Lower Respiratory Tract Infection

The circadian rhythm is a biological system that creates daily variations of physiology and behavior with a 24-h cycle, which is precisely controlled by the molecular circadian clock. The circadian clock dominates temporal activity of physiological homeostasis at the molecular level, including endocrine secretion, metabolic, immune response, coupled with extrinsic environmental cues (e.g., light/dark cycles) and behavioral cues (e.g., sleep/wake cycles and feeding/fasting cycles). The other side of the clock is that the misaligned circadian rhythm contributes to the onset of a variety of diseases, such as cancer, metabolic diseases, and cardiovascular diseases, the acceleration of aging, and the development of systemic inflammation. The role played by macrophages is a key mediator between circadian disruption and systemic inflammation. At the molecular level, macrophage functions are under the direct control of the circadian clock, and thus the circadian misalignment remodels the phenotype of macrophages toward a ‘killer’ mode. Remarkably, the inflammatory macrophages induce systemic and chronic inflammation, leading to the development of inflammatory diseases and the dampened immune defensive machinery against infectious diseases such as COVID-19. Here, we discuss how the circadian clock regulates macrophage immune functions and provide the potential risk of misaligned circadian rhythms against inflammatory and infectious diseases.

Circulating Lymphocyte Trafficking to the Bone Marrow Contributes to Lymphopenia in Myocardial Infarction

Some patients with myocardial infarction (MI) exhibit lymphopenia, a reduction in blood lymphocyte count. Moreover, lymphopenia inversely correlates with patient prognosis. The objective of this study was to elucidate the underlying mechanisms that cause lymphopenia after MI. Multiparameter flow cytometric analysis demonstrated that MI induced profound B and T lymphopenia in a mouse model, peaking at day 1 post-MI. The finding that non-MI control and MI mice exhibited similar apoptotic rate for blood B and T lymphocytes argues against apoptosis being essential for MI-induced lymphopenia. Interestingly, the bone marrow in day 1 post-MI mice contained more B and T cells but showed less B and T cell proliferation, compared to day 0 controls. This suggests that blood lymphocytes may travel to the bone marrow after MI. This was confirmed by adoptive transfer experiments demonstrating that MI caused the loss of transferred lymphocytes in the blood, but the accumulation of transferred lymphocytes in the bone marrow. To elucidate the underlying signaling pathways, β2 adrenergic receptor or sphingoshine-1-phosphate receptor type 1 (S1PR1) was pharmacologically blocked respectively. β2 receptor inhibition had no significant effect on blood lymphocyte count, whereas S1PR1 blockade aggravated lymphopenia in MI mice. Further, we discovered that MI-induced glucocorticoid release triggered lymphopenia. This was supported by the findings that adrenalectomy (ADX) completely prevented mice from MI-induced lymphopenia, and supplementation with corticosterone in adrenalectomized MI mice re-induced lymphopenia. In conclusion, our study demonstrates that MI-associated lymphopenia involves lymphocyte redistribution from peripheral blood to the bone marrow, which is mediated by glucocorticoids.

Control of immunity via nutritional interventions

Nutrition affects all physiological processes including those linked to the development and function of our immune system. Here, we discuss recent evidence and emerging concepts supporting the idea that our newfound relationship with nutrition in industrialized countries has fundamentally altered the way in which our immune system is wired. This will be examined through the lens of studies showing that mild or transient reductions in dietary intake can enhance protective immunity while also limiting aberrant inflammatory responses. We will further discuss how trade-offs and priorities begin to emerge in the context of severe nutritional stress. In those settings, specific immunological functions are heightened to re-enforce processes and tissue sites most critical to survival. Altogether, these examples will emphasize the profound influence nutrition has over the immune system and highlight how a mechanistic exploration of this cross talk could ultimately lead to the design of novel therapeutic approaches that prevent and treat disease.

The contribution of sleep to the neuroendocrine regulation of rhythms in human leukocyte traffic

Twenty-four-hour rhythms in immune parameters and functions are robustly observed phenomena in biomedicine. Here, we summarize the important role of sleep and associated parameters on the neuroendocrine regulation of rhythmic immune cell traffic to different compartments, with a focus on human leukocyte subsets. Blood counts of "stress leukocytes" such as neutrophils, natural killer cells, and highly differentiated cytotoxic T cells present a rhythm with a daytime peak. It is mediated by morning increases in epinephrine, leading to a mobilization of these cells out of the marginal pool into the circulation following a fast, beta2-adrenoceptor-dependent inhibition of adhesive integrin signaling. In contrast, other subsets such as eosinophils and less differentiated T cells are redirected out of the circulation during daytime. This is mediated by stimulation of the glucocorticoid receptor following morning increases in cortisol, which promotes CXCR4-driven leukocyte traffic, presumably to the bone marrow. Hence, these cells show highest numbers in blood at night when cortisol levels are lowest. Sleep adds to these rhythms by actively suppressing epinephrine and cortisol levels. In addition, sleep increases levels of immunosupportive mediators, such as aldosterone and growth hormone, which are assumed to promote T-cell homing to lymph nodes, thus facilitating the initiation of adaptive immune responses during sleep. Taken together, sleep-wake behavior with its unique neuroendocrine changes regulates human leukocyte traffic with overall immunosupportive effects during nocturnal sleep. In contrast, integrin de-activation and redistribution of certain leukocytes to the bone marrow during daytime activity presumably serves immune regulation and homeostasis.

The involvement of host circadian clocks in the regulation of the immune response to parasitic infections in mammals

Circadian rhythms are recurring variations of physiology with a period of ~24 hours, generated by circadian clocks located throughout the body. Studies have shown a circadian regulation of many aspects of immunity. Immune cells have intrinsic clock mechanisms, and innate and adaptive immune responses - such as leukocyte migration, magnitude of inflammation, cytokine production and cell differentiation - are under circadian control. This circadian regulation has consequences for infections including parasitic infections. In the context of Leishmania infection, the circadian clock within host immune cells modulates the magnitude of the infection and the inflammatory response triggered by the parasite. As for malaria, rhythms within the immune system were shown to impact the developmental cycles of Plasmodium parasites within red blood cells. Further, host circadian rhythms impact infections by multicellular parasites; for example, infection with helminth Trichuris muris shows different kinetics of worm expulsion depending on time of day of infection, a variation that depends on the dendritic cell clock. Although the research on the circadian control of immunity in the context of parasitic infections is in its infancy, the research reviewed here suggests a crucial involvement of host circadian rhythms in immunity on the development and progression of parasitic infections.

The Broad Immunomodulatory Effects of IL-7 and Its Application In Vaccines

Interleukin-7 (IL-7) is produced by stromal cells, keratinocytes, and epithelial cells in host tissues or tumors and exerts a wide range of immune effects mediated by the IL-7 receptor (IL-7R). IL-7 is primarily involved in regulating the development of B cells, T cells, natural killer cells, and dendritic cells via the JAK-STAT, PI3K-Akt, and MAPK pathways. This cytokine participates in the early generation of lymphocyte subsets and maintain the survival of all lymphocyte subsets; in particular, IL-7 is essential for orchestrating the rearrangement of immunoglobulin genes and T-cell receptor genes in precursor B and T cells, respectively. In addition, IL-7 can aid the activation of immune cells in anti-virus and anti-tumor immunity and plays important roles in the restoration of immune function. These biological functions of IL-7 make it an important molecular adjuvant to improve vaccine efficacy as it can promote and extend systemic immune responses against pathogens by prolonging lymphocyte survival, enhancing effector cell activity, and increasing antigen-specific memory cell production. This review focuses on the biological function and mechanism of IL-7 and summarizes its contribution towards improved vaccine efficacy. We hope to provide a thorough overview of this cytokine and provide strategies for the development of the future vaccines.

Glucocorticoid production in the thymus and brain: Immunosteroids and neurosteroids

Glucocorticoids (GCs) regulate a myriad of physiological systems, such as the immune and nervous systems. Systemic GC levels in blood are often measured as an indicator of local GC levels in target organs. However, several extra-adrenal organs can produce and metabolize GCs locally. More sensitive and specific methods for GC analysis (i.e., mass spectrometry) allow measurement of local GC levels in small tissue samples with low GC concentrations. Consequently, is it now apparent that systemic GC levels often do not reflect local GC levels. Here, we review the use of systemic GC measurements in clinical and research settings, discuss instances where systemic GC levels do not reflect local GC levels, and present evidence that local GC levels provide useful insights, with a focus on local GC production in the thymus (immunosteroids) and brain (neurosteroids). Lastly, we suggest key areas for further research, such as the roles of immunosteroids and neurosteroids in neonatal programming and the potential clinical relevance of local GC modulators.

Circadian rhythms in adaptive immunity and vaccination

Adaptive immunity allows an organism to respond in a specific manner to pathogens and other non-self-agents. Also, cells of the adaptive immune system, such as T and B lymphocytes, can mediate a memory of an encounter with a pathogen, allowing a more efficient response to a future infection. As for other aspects of physiology and of the immune system, the adaptive immune system is regulated by circadian clocks. Consequently, the development, differentiation, and trafficking between tissues of adaptive immune cells have been shown to display daily rhythms. Also, the response of T cells to stimuli (e.g., antigen presentation to T cells by dendritic cells) varies according to a circadian rhythm, due to T cell-intrinsic mechanisms as well as cues from other tissues. The circadian control of adaptive immune response has implications for our understanding of the fight against pathogens as well as auto-immune diseases, but also for vaccination, a preventive measure based on the development of immune memory.