Periodicity of susceptibility to pneumococcal infection: influence of light and adrenocortical secretions

BMAL1 plays a crucial role in immune homeostasis during sepsis-induced acute lung injury

Sepsis is a widespread and life-threatening disease characterised by infection-triggered immune hyperactivation and cytokine storms, culminating in tissue damage and multiple organ dysfunction syndrome. BMAL1 is a pivotal transcription factor in the circadian clock that plays a crucial role in maintaining immune homeostasis. BMAL1 dysregulation has been implicated in inflammatory diseases and immunodeficiency. However, the mechanisms underlying BMAL1 disruption in sepsis-induced acute lung injury (ALI) remain poorly understood. In vitro, we used THP1 and mouse peritoneal macrophages to elucidate the potential mechanism of BMAL1 function in sepsis. In vivo, an endotoxemia model was used to investigate the effect of BMAL1 on sepsis and the therapeutic role of targeting CXCR2. We showed that BMAL1 significantly affected the regulation of innate immunity in sepsis-induced ALI. BMAL1 deficiency in the macrophages exacerbated systemic inflammation and sepsis-induced ALI. Mechanistically, BMAL1 acted as a transcriptional suppressor and regulated the expression of CXCL2. BMAL1 deficiency in macrophages upregulated CXCL2 expression, increasing the recruitment of polymorphonuclear neutrophils and the formation of neutrophil extracellular traps (NETs) by binding to the chemokine receptor CXCR2, thereby intensifying lung injury in a sepsis model. Furthermore, a selective inhibitor of CXCR2, SB225002, exerted promising therapeutic effects by markedly reducing neutrophil infiltration and NETs formation and alleviating lung injury. Importantly, CXCR2 blockade mitigated multiple organ dysfunction. Collectively, these findings suggest that BMAL1 controls the CXCL2/CXCR2 pathway, and the therapeutic efficacy of targeting CXCR2 in sepsis has been validated, presenting BMAL1 as a potential therapeutic target for lethal infections.

Circadian disruption dysregulates lung gene expression associated with inflammatory lung injury

Rationale

Circadian systems drive the expression of multiple genes in nearly all cells and coordinate cellular-, tissue-, and system-level processes that are critical to innate immunity regulation.

Objective

We examined the effects of circadian rhythm disorganization, produced by light shift exposure, on innate immunity-mediated inflammatory lung responses including vascular permeability and gene expression in a C57BL/6J murine model of inflammatory lung injury.

Methods

A total of 32 C57BL/6J mice were assigned to circadian phase shifting (CPS) with intratracheal phosphate-buffered saline (PBS), CPS with intratracheal lipopolysaccharide (LPS), control (normal lighting) condition with intratracheal PBS, and control condition with intratracheal LPS. Bronchoalveolar lavage (BAL) protein, cell counts, tissue immunostaining, and differentially expressed genes (DEGs) were measured in lung tissues at 2 and 10 weeks.

Measurements and results

In mice exposed to both CPS and intratracheal LPS, both BAL protein and cell counts were increased at both 2 and 10 weeks compared to mice exposed to LPS alone. Multiple DEGs were identified in CPS-LPS-exposed lung tissues compared to LPS alone and were involved in transcriptional pathways associated with circadian rhythm disruption, regulation of lung permeability, inflammation with Rap1 signaling, and regulation of actin cytoskeleton. The most dysregulated pathways included myosin light chain kinase, MAP kinase, profilin 2, fibroblast growth factor receptor, integrin b4, and p21-activated kinase.

Conclusion

Circadian rhythm disruption results in exacerbated immune response and dysregulated expression of cytoskeletal genes involved in the regulation of epithelial and vascular barrier integrity-the mechanistic underpinnings of acute lung injury. Further studies need to explore circadian disorganization as a druggable target.

PER2/P65-driven glycogen synthase 1 transcription in macrophages modulates gut inflammation and pathogenesis of rectal prolapse

Rectal prolapse in serious inflammatory bowel disease is caused by abnormal reactions of the intestinal mucosal immune system. The circadian clock has been implicated in immune defense and inflammatory responses, but the mechanisms by which it regulates gut inflammation remain unclear. In this study, we investigate the role of the rhythmic gene Period2 (Per2) in triggering inflammation in the rectum and its contribution to the pathogenesis of rectal prolapse. We report that Per2 deficiency in mice increased susceptibility to intestinal inflammation and resulted in spontaneous rectal prolapse. We further demonstrated that PER2 was essential for the transcription of glycogen synthase 1 by interacting with the NF-κB p65. We show that the inhibition of Per2 reduced the levels of glycogen synthase 1 and glycogen synthesis in macrophages, impairing the capacity of pathogen clearance and disrupting the composition of gut microbes. Taken together, our findings identify a novel role for Per2 in regulating the capacity of pathogen clearance in macrophages and gut inflammation and suggest a potential animal model that more closely resembles human rectal prolapse.

Effects of light and circadian clock on the antiviral immune response in zebrafish

The circadian clock mechanism, which is evolutionarily conserved across various organisms, plays a crucial role in synchronizing physiological responses to external conditions, primarily in response to light availability. By maintaining homeostasis of biological processes and behavior, the circadian clock serves as a key regulator. This biological mechanism also coordinates diurnal oscillations of the immune response during infections. However there is limited information available regarding the influence of circadian oscillation on immune regulation, especially in lower vertebrates like teleost fish. Therefore, the present study aimed to investigate the effects of light and the timing of infection induction on the antiviral immune response in zebrafish. To explore the relationship between the timing of infection and the response activated by viral pathogens, we used a zebrafish model infected with tilapia lake virus (TiLV). Our findings demonstrated that light availability significantly affects the antiviral immune response and the functioning of the molecular clock mechanism during TiLV infection. This is evident through alterations in the expression of major core clock genes and the regulation of TiLV replication and type I IFN pathway genes in the kidney of fish maintained under LD (light-dark) conditions compared to constant darkness (DD) conditions. Moreover, infection induced during the light phase of the LD cycle, in contrast to nocturnal infection, also exhibited similar effects on the expression of genes associated with the antiviral response. This study indicates a more effective mechanism of the zebrafish antiviral response during light exposure, which inherently involves modification of the expression of key components of the molecular circadian clock. It suggests that the zebrafish antiviral response to infection is regulated by both light and the circadian clock.

The circadian neutrophil, inside-out

The circadian clock has sway on a myriad of physiological targets, among which the immune and inflammatory systems are particularly prominent. In this review, we discuss how neutrophils, the wildcard of the immune system, are regulated by circadian oscillations. We describe cell-intrinsic and extrinsic diurnal mechanisms governing the general physiology and function of these cells, from purely immune to homeostatic. Repurposing the concepts discovered in other cell types, we then speculate on various uncharted avenues of neutrophil-circadian relationships, such as topology, metabolism, and the regulation of tissue clocks, with the hope of identifying exciting new avenues of work in the context of circadian immunity.

Clock in radiation oncology clinics: cost-free modality to alleviate treatment-related toxicity

A large number of studies have reported that tumor cells are often out of sync with the surrounding healthy tissue. Exploiting this misalignment may be a way to obtain a substantial gain in the therapeutic window. Specifically, based on reports to date, we will assess whether radiotherapy outcomes differ depending on the administration time. Collectively, 24 studies met the inclusion criteria, out of which 12 at least reported that radiation therapy is less toxic when administered at a particular time, probably because there is less collateral damage to healthy cells. However, discrepancies exist across studies and urge further investigation. Mechanistic studies elucidating the relationship between radiotherapy, circadian rhythms, and cell cycle, combined with either our “digital” or “biological” chronodata, would help oncologists successfully chronotype individual patients and strategize treatment plans accordingly.

Diurnal Differences in Intracellular Replication Within Splenic Macrophages Correlates With the Outcome of Pneumococcal Infection

Circadian rhythms affect the progression and severity of bacterial infections including those caused by Streptococcus pneumoniae, but the mechanisms responsible for this phenomenon remain largely elusive. Following advances in our understanding of the role of replication of S. pneumoniae within splenic macrophages, we sought to investigate whether events within the spleen correlate with differential outcomes of invasive pneumococcal infection. Utilising murine invasive pneumococcal disease (IPD) models, here we report that infection during the murine active phase (zeitgeber time 15; 15h after start of light cycle, 3h after start of dark cycle) resulted in significantly faster onset of septicaemia compared to rest phase (zeitgeber time 3; 3h after start of light cycle) infection. This correlated with significantly higher pneumococcal burden within the spleen of active phase-infected mice at early time points compared to rest phase-infected mice. Whole-section confocal microscopy analysis of these spleens revealed that the number of pneumococci is significantly higher exclusively within marginal zone metallophilic macrophages (MMMs) known to allow intracellular pneumococcal replication as a prerequisite step to the onset of septicaemia. Pneumococcal clusters within MMMs were more abundant and increased in size over time in active phase-infected mice compared to those in rest phase-infected mice which decreased in size and were present in a lower percentage of MMMs. This phenomenon preceded significantly higher levels of bacteraemia alongside serum IL-6 and TNF-α concentrations in active phase-infected mice following re-seeding of pneumococci into the blood. These data greatly advance our fundamental knowledge of pneumococcal infection by linking susceptibility to invasive pneumococcal infection to variation in the propensity of MMMs to allow persistence and replication of phagocytosed bacteria. These findings also outline a somewhat rare scenario whereby the active phase of an organism’s circadian cycle plays a seemingly counterproductive role in the control of invasive infection.

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.

Circadian rhythms in immunity and host-parasite interactions

The mammalian immune system adheres to a 24 h circadian schedule, exhibiting daily rhythmic patterns in homeostatic immune processes, such as immune cell trafficking, as well as the inflammatory response to infection. These diurnal rhythms are driven by endogenous molecular clocks within immune cells which are hierarchically coordinated by a light-entrained central clock in the suprachiasmatic nucleus of the hypothalamus and responsive to local rhythmic cues including temperature, hormones and feeding time. Circadian control of immunity may enable animals to anticipate daily pathogenic threat from parasites and gate the magnitude of the immune response, potentially enhancing fitness. However, parasites also strive for optimum fitness and some may have co-evolved to benefit from host circadian timing mechanisms, possibly via the parasites' own intrinsic molecular clocks. In this review, we summarize the current knowledge surrounding the influence of the circadian clock on the mammalian immune system and the host-parasitic interaction. We also discuss the potential for chronotherapeutic strategies in the treatment of parasitic diseases.

Circadian Clock Regulates Inflammation and the Development of Neurodegeneration

The circadian clock regulates numerous key physiological processes and maintains cellular, tissue, and systemic homeostasis. Disruption of circadian clock machinery influences key activities involved in immune response and brain function. Moreover, Immune activation has been closely linked to neurodegeneration. Here, we review the molecular clock machinery and the diurnal variation of immune activity. We summarize the circadian control of immunity in both central and peripheral immune cells, as well as the circadian regulation of brain cells that are implicated in neurodegeneration. We explore the important role of systemic inflammation on neurodegeneration. The circadian clock modulates cellular metabolism, which could be a mechanism underlying circadian control. We also discuss the circadian interventions implicated in inflammation and neurodegeneration. Targeting circadian clocks could be a potential strategy for the prevention and treatment of inflammation and neurodegenerative diseases.

Seasonal and daytime variation in multiple immune parameters in humans: Evidence from 329,261 participants of the UK Biobank cohort

Seasonal disease outbreaks are perennial features of human infectious disease but the factors generating these patterns are unclear. Here we investigate seasonal and daytime variability in multiple immune parameters in 329,261 participants in UK Biobank and test for associations with a wide range of environmental and lifestyle factors, including changes in day length, outdoor temperature and vitamin D at the time the blood sample was collected. Seasonal patterns were evident in lymphocyte and neutrophil counts, and C-reactive protein CRP, but not monocytes, and these were independent of lifestyle, demographic, and environmental factors. All the immune parameters assessed demonstrated significant daytime variation that was independent of confounding factors. At a population level, human immune parameters vary across season and across time of day, independent of multiple confounding factors. Both season and time of day are fundamental dimensions of immune function that should be considered in all studies of immuno-prophylaxis and disease transmission.

Modeling the circadian regulation of the immune system: Sexually dimorphic effects of shift work

The circadian clock exerts significance influence on the immune system and disruption of circadian rhythms has been linked to inflammatory pathologies. Shift workers often experience circadian misalignment as their irregular work schedules disrupt the natural light-dark cycle, which in turn can cause serious health problems associated with alterations in genetic expressions of clock genes. In particular, shift work is associated with impairment in immune function, and those alterations are sex-specific. The goal of this study is to better understand the mechanisms that explain the weakened immune system in shift workers. To achieve that goal, we have constructed a mathematical model of the mammalian pulmonary circadian clock coupled to an acute inflammation model in the male and female rats. Shift work was simulated by an 8h-phase advance of the circadian system with sex-specific modulation of clock genes. The model reproduces the clock gene expression in the lung and the immune response to various doses of lipopolysaccharide (LPS). Under normal conditions, our model predicts that a host is more sensitive to LPS at circadian time (CT) CT12 versus CT0 due to a dynamic change of Interleukin 10 (IL-10), an anti-inflammatory cytokine. We identify REV-ERB as a key modulator of IL-10 activity throughout the circadian day. The model also predicts a reversal of the times of lowest and highest sensitivity to LPS, with males and females exhibiting an exaggerated response to LPS at CT0, which is countered by a blunted immune response at CT12. Overall, females produce fewer pro-inflammatory cytokines than males, but the extent of sequelae experienced by males and females varies across the circadian day. This model can serve as an essential component in an integrative model that will yield mechanistic understanding of how shift work-mediated circadian disruptions affect the inflammatory and other physiological responses.

For Whom the Clock Ticks: Clinical Chronobiology for Infectious Diseases

The host defense against pathogens varies among individuals. Among the factors influencing host response, those associated with circadian disruptions are emerging. These latter depend on molecular clocks, which control the two partners of host defense: microbes and immune system. There is some evidence that infections are closely related to circadian rhythms in terms of susceptibility, clinical presentation and severity. In this review, we overview what is known about circadian rhythms in infectious diseases and update the knowledge about circadian rhythms in immune system, pathogens and vectors. This heuristic approach opens a new fascinating field of time-based personalized treatment of infected patients.

Winter is coming: Pathogen emergence in seasonal environments

Many infectious diseases exhibit seasonal dynamics driven by periodic fluctuations of the environment. Predicting the risk of pathogen emergence at different points in time is key for the development of effective public health strategies. Here we study the impact of seasonality on the probability of emergence of directly transmitted pathogens under different epidemiological scenarios. We show that when the period of the fluctuation is large relative to the duration of the infection, the probability of emergence varies dramatically with the time at which the pathogen is introduced in the host population. In particular, we identify a new effect of seasonality (the winter is coming effect) where the probability of emergence is vanishingly small even though pathogen transmission is high. We use this theoretical framework to compare the impact of different preventive control strategies on the average probability of emergence. We show that, when pathogen eradication is not attainable, the optimal strategy is to act intensively in a narrow time interval. Interestingly, the optimal control strategy is not always the strategy minimizing R₀, the basic reproduction ratio of the pathogen. This theoretical framework is extended to study the probability of emergence of vector borne diseases in seasonal environments and we show how it can be used to improve risk maps of Zika virus emergence.

Seasonality drives fluctuations in the probability of pathogen emergence, with dramatic consequences for public health and agriculture. We show that this probability of pathogen emergence can be vanishingly small before the low transmission season. We derive the conditions for the existence of this winter is coming effect and identify optimal control strategies that minimize the risk of pathogen emergence. We generalize this framework to account for different forms of environmental variations, different modes of control and complex pathogen life cycles. We illustrate how this framework can be used to improve predictions of Zika emergence at different points in space and time.

Time after time: circadian clock regulation of intestinal stem cells

Daily fluctuations in animal physiology, known as circadian rhythms, are orchestrated by a conserved molecular timekeeper, known as the circadian clock. The circadian clock forms a transcription-translation feedback loop that has emerged as a central biological regulator of many 24-h processes. Early studies of the intestine discovered that many digestive functions have a daily rhythm and that intestinal cell production was similarly time-dependent. As genetic methods in model organisms have become available, it has become apparent that the circadian clock regulates many basic cellular functions, including growth, proliferation, and differentiation, as well as cell signalling and stem cell self-renewal. Recent connections between circadian rhythms and immune system function, and between circadian rhythms and microbiome dynamics, have also been revealed in the intestine. These processes are highly relevant in understanding intestinal stem cell biology. Here we describe the circadian clock regulation of intestinal stem cells primarily in two model organisms: Drosophila melanogaster and mice. Like all cells in the body, intestinal stem cells are subject to circadian timing, and both cell-intrinsic and cell-extrinsic circadian processes contribute to their function.

Microbes in the Era of Circadian Medicine

The organisms of most domains of life have adapted to circadian changes of the environment and regulate their behavior and physiology accordingly. A particular case of such paradigm is represented by some types of host-pathogen interaction during infection. Indeed, not only some hosts and pathogens are each endowed with their own circadian clock, but they are also influenced by the circadian changes of the other with profound consequences on the outcome of the infection. It comes that daily fluctuations in the availability of resources and the nature of the immune response, coupled with circadian changes of the pathogen, may influence microbial virulence, level of colonization and damage to the host, and alter the equilibrium between commensal and invading microorganisms. In the present review, we discuss the potential relevance of circadian rhythms in human bacterial and fungal pathogens, and the consequences of circadian changes of the host immune system and microbiome on the onset and development of infection. By looking from the perspective of the interplay between host and microbes circadian rhythms, these concepts are expected to change the way we approach human infections, not only by predicting the outcome of the host-pathogen interaction, but also by indicating the best time for intervention to potentiate the anti-microbial activities of the immune system and to weaken the pathogen when its susceptibility is higher.

Circadian and circannual timescales interact to generate seasonal changes in immune function

Annual changes in day length enhance or suppress diverse aspects of immune function, giving rise to seasonal cycles of illness and mortality. The daily light-dark cycle also entrains circadian rhythms in immunity. Most published reports on immunological seasonality rely on measurements or interventions performed only at one point in the day. Because there can be no perfect matching of circadian phase across photoperiods of different duration, the manner in which these timescales interact to affect immunity is not understood. We examined whether photoperiodic changes in immune function reflect phenotypic changes that persist throughout the daily cycle, or merely reflect photoperiodic shifts in the circadian phase alignment of immunological rhythms. Diurnal rhythms in blood leukocyte trafficking, infection induced sickness responses, and delayed-type hypersensitivity skin inflammatory responses were examined at high-frequency sampling intervals (every 3 h) in Siberian hamsters (Phodopus sungorus) following immunological adaptation to summer or winter photoperiods. Photoperiod profoundly enhanced or suppressed immune function, in a trait-specific manner, and we were unable to identify a phase alignment of diurnal waveforms which eliminated these enhancing and suppressing effects of photoperiod. These results support the hypothesis that seasonal timescales affect immunity via mechanisms independent of circadian entrainment of the immunological circadian waveform.

Dawn to Dusk: Diurnal Rhythm of the Immune Response in Rainbow Trout (Oncorhynchus Mykiss)

The daily change of light and dark periods influences different physiological processes including feeding, resting and locomotor activity. Previously, several studies on mammalian models revealed a strong link between day-night rhythms and key immunological parameters. Since teleost fishes possess innate and adaptive immune responses like those observed in higher vertebrates, we aimed to elucidate how changes in light-dark cycles shape the immune system of fish. Using the rainbow trout laboratory model, we investigated the link between diurnal rhythms and immune competence of fish. Initially, the cell composition and phagocytic activity of leukocytes was analyzed in the circulation as well as in the head kidney, the functional ortholog of mammalian bone marrow. Once the baseline was established, we evaluated the ability of fish to respond to a bacterial stimulus, as well as the changes in antimicrobial activity of the serum. Our results suggest increased immune competence during the day, manifested by the higher presence of myeloid cells in the circulation; increased overall phagocytic activity; and higher capacity of the sera to inhibit the growth of Aeromonas salmonicida. Notably, our flow cytometric analysis identified the myeloid cells as the major population influenced by the time of day, whereas IgM⁺ B cells and thrombocytes did not vary in a significant manner. Interestingly, the presence of myeloid cells in blood and head kidney followed complementary trends. Thus, while we observed the highest number of myeloid cells in the blood during early morning, we witnessed a reverse trend in the head kidney, suggesting a homing of myeloid cells to reservoir niches with the onset of the dark phase. Further, the presence of myeloid cells was mirrored in the expression of the proinflammatory marker tnfa as well as in the number of leukocytes recruited to the peritoneal cavity in the peritonitis model of inflammation. Overall, the data suggest a connection between diurnal rhythms and the immune response of rainbow trout and highlight the relevance of rhythmicity and its influence on experimental work in the field of fish chronoimmunology.

Circadian Rhythms Have Effects on Surgical Outcomes of Liver Transplantation for Patients With Hepatocellular Carcinoma: A Retrospective Analysis of 147 Cases in a Single Center

AIM

To investigate the impact of circadian rhythms on the outcomes of liver transplantation on patients suffering from hepatocellular carcinoma (HCC).

METHODS

We retrospectively reviewed data of patients who underwent liver transplantation from 2012 to 2017 in our center. Based on the begin time of transplantation, these patients were separated into 2 groups: day group and night group. The intraoperative and postoperative clinical variables were analyzed to find out the impact of the circadian rhythms. Multivariate analysis was performed to examine strength associations between the begin time of operation and surgical outcomes.

RESULTS

A total of 147 patients were included in this study: 102 patients in the day group and 45 patients in the night group. Compared with the day group, patients in the night group had higher incidence of intraoperative massive hemorrhage (11.1% vs 2.0%, P = .048), more intraoperative blood loss (2168.00 ± 2324.20 mL vs 1405.88 ± 1037.69 mL, P = .040), and more requirement of red blood cells (RBC) suspension (8.59 ± 7.11 u vs 6.37 ± 5.78 u, P = .048). In addition, total operation time in the night group was longer than that in the day group (8.90 ± 1.65 hours vs 8.26 ± 1.69 hours, P = .034), as well as the cold ischemia time (9.35 ± 5.03 hours vs 7.21 ± 3.93 hours, P = .014). Furthermore, the night group had higher incidence of other intraoperative complications (13.3% vs 2.9%, P = .038), postoperative abdominal infection (20.0% vs 6.9%, P = .038), and more hospital cost (37,357.96 ± 6779.96 dollars vs 33,551.75 ± 11,683.38 dollars, P = .045). Moreover, patients in the night group needed longer time to restore hepatic function to normal (21.77 ± 10.91 days vs 17.54 ± 10.80 days, P = .033). Multivariate analysis showed that begin time of operation was the independent risk factor of longer operation time, more blood loss during operation, higher incidence of massive hemorrhage and other intraoperative complications, longer time for restoration of hepatic function to normal, higher incidence of abdominal infection at the early stage after transplantation, and more hospital cost (all P value ≤ .05).

CONCLUSION

Liver transplantation performed at night was associated with higher incidence of intraoperative and early postoperative complications, as well as higher hospital cost. And these worsened outcomes all could be explained by the influence that circadian rhythms had on patients or medical workers.

Diurnal Variation in Systemic Acute Inflammation and Clinical Outcomes Following Severe Blunt Trauma

Animal studies suggest that the time of day is a determinant of the immunological response to both injury and infection. We hypothesized that due to this diurnal variation, time of injury could affect the systemic inflammatory response and outcomes post-trauma and tested this hypothesis by examining the dynamics of circulating inflammatory mediators in blunt trauma patients injured during daytime vs. nighttime. From a cohort of 472 blunt trauma survivors, two stringently matched sub-cohorts of moderately/severely injured patients [injury severity score (ISS) >20] were identified. Fifteen propensity-matched, daytime-inured (“mDay”) patients (age 43.6 ± 5.2, M/F 11/4, ISS 22.9 ± 0.7) presented during the shortest local annual period (8:00 am−5:00 pm), and 15 propensity-matched “mNight” patients (age 43 ± 4.3, M/F 11/4, ISS 24.5 ± 2.5) presented during the shortest night period (10:00 pm−5:00 am). Serial blood samples were obtained (3 samples within the first 24 h and daily from days 1–7) from all patients. Thirty-two plasma inflammatory mediators were assayed. Two-way Analysis of Variance (ANOVA) was used to compare groups. Dynamic Network Analysis (DyNA) and Dynamic Bayesian Network (DyBN) inference were utilized to infer dynamic interrelationships among inflammatory mediators. Both total hospital and intensive care unit length of stay were significantly prolonged in the mNight group. Circulating IL-17A was elevated significantly in the mNight group from 24 h to 7 days post-injury. Circulating MIP-1α, IL-7, IL-15, GM-CSF, and sST2 were elevated in the mDay group. DyNA demonstrated elevated network complexity in the mNight vs. the mDay group. DyBN suggested that cortisol and sST2 were central nodes upstream of TGF-β1, chemokines, and Th17/protective mediators in both groups, with IL-6 being an additional downstream node in the mNight group only. Our results suggest that time of injury affects clinical outcomes in severely injured patients in a manner associated with an altered systemic inflammation program, possibly implying a role for diurnal or circadian variation in the response to traumatic injury.

Effect of Time of Day of Infection on Chlamydia Infectivity and Pathogenesis

Genital chlamydia infection in women causes complications such as pelvic inflammatory disease and tubal factor infertility, but it is unclear why some women are more susceptible than others. Possible factors, such as time of day of chlamydia infection on chlamydial pathogenesis has not been determined. We hypothesised that infections during the day, will cause increased complications compared to infections at night. Mice placed under normal 12:12 light: dark (LD) cycle were infected intravaginally with Chlamydia muridarum either at zeitgeber time 3, ZT3 and ZT15. Infectivity was monitored by periodic vaginal swabs and chlamydiae isolation. Blood and vaginal washes were collected for host immunologic response assessments. The reproductive tracts of the mice were examined histopathologically, and fertility was determined by embryo enumeration after mating. Mice infected at ZT3 shed significantly more C. muridarum than mice infected at ZT15. This correlated with the increased genital tract pathology observed in mice infected at ZT3. Mice infected at ZT3 were less fertile than mice infected at ZT15. The results suggest that the time of day of infection influences chlamydial pathogenesis, it indicates a possible association between complications from chlamydia infection and host circadian clock, which may lead to a better understanding of chlamydial pathogenesis.

Clocking in to immunity

Circadian rhythms are a ubiquitous feature of virtually all living organisms, regulating a wide diversity of physiological systems. It has long been established that the circadian clockwork plays a key role in innate immune responses, and recent studies reveal that several aspects of adaptive immunity are also under circadian control. We discuss the latest insights into the genetic and biochemical mechanisms linking immunity to the core circadian clock of the cell and hypothesize as to why the immune system is so tightly controlled by circadian oscillations. Finally, we consider implications for human health, including vaccination strategies and the emerging field of chrono-immunotherapy.

Characterizing and Comparing the Seasonality of Influenza-Like Illnesses and Invasive Pneumococcal Diseases Using Seasonal Waveforms

The seasonalities of influenza-like illnesses (ILIs) and invasive pneumococcal diseases (IPDs) remain incompletely understood. Experimental evidence indicates that influenza-virus infection predisposes to pneumococcal disease, so that a correspondence in the seasonal patterns of ILIs and IPDs might exist at the population level. We developed a method to characterize seasonality by means of easily interpretable summary statistics of seasonal shape-or seasonal waveforms. Nonlinear mixed-effects models were used to estimate those waveforms based on weekly case reports of ILIs and IPDs in 5 regions spanning continental France from July 2000 to June 2014. We found high variability of ILI seasonality, with marked fluctuations of peak amplitudes and peak times, but a more conserved epidemic duration. In contrast, IPD seasonality was best modeled by a markedly regular seasonal baseline, punctuated by 2 winter peaks in late December to early January and January to February. Comparing ILI and IPD seasonal waveforms, we found indication of a small, positive correlation. Direct models regressing IPDs on ILIs provided comparable results, even though they estimated moderately larger associations. The method proposed is broadly applicable to diseases with unambiguous seasonality and is well-suited to analyze spatially or temporally grouped data, which are common in epidemiology.

Perspectives on the relevance of the circadian time structure to workplace threshold limit values and employee biological monitoring

The circadian time structure (CTS) and its disruption by rotating and nightshift schedules relative to work performance, accident risk, and health/wellbeing have long been areas of occupational medicine research. Yet, there has been little exploration of the relevance of the CTS to setting short-term, time-weighted, and ceiling threshold limit values (TLVs); conducting employee biological monitoring (BM); and establishing normative reference biological exposure indices (BEIs). Numerous publications during the past six decades document the CTS substantially affects the disposition - absorption, distribution, metabolism, and elimination - and effects of medications. Additionally, laboratory animal and human studies verify the tolerance to chemical, biological (contagious), and physical agents can differ extensively according to the circadian time of exposure. Because of slow and usually incomplete CTS adjustment by rotating and permanent nightshift workers, occupational chemical and other contaminant encounters occur during a different circadian stage than for dayshift workers. Thus, the intended protection of some TLVs when working the nightshift compared to dayshift might be insufficient, especially in high-risk settings. The CTS is germane to employee BM in that large-amplitude predictable-in-time 24h variation can occur in the concentration of urine, blood, and saliva of monitored chemical contaminants and their metabolites plus biomarkers indicative of adverse xenobiotic exposure. The concept of biological time-qualified (for rhythms) reference values, currently of interest to clinical laboratory pathology practice, is seemingly applicable to industrial medicine as circadian time and workshift-specific BEIs to improve surveillance of night workers, in particular. Furthermore, BM as serial assessments performed frequently both during and off work, exemplified by employee self-measurement of lung function using a small portable peak expiratory flow meter, can easily identify intolerance before induction of pathology.

The innate immune cell response to bacterial infection in larval zebrafish is light-regulated

The circadian clock, which evolved to help organisms harmonize physiological responses to external conditions (such as the light/dark cycle, LD), is emerging as an important regulator of the immune response to infection. Gaining a complete understanding of how the circadian clock influences the immune cell response requires animal models that permit direct observation of these processes within an intact host. Here, we investigated the use of larval zebrafish, a powerful live imaging system, as a new model to study the impact of a fundamental zeitgeber, light, on the innate immune cell response to infection. Larvae infected during the light phase of the LD cycle and in constant light condition (LL) demonstrated enhanced survival and bacterial clearance when compared with larvae infected during the dark phase of the LD cycle and in constant dark condition (DD). This increased survival was associated with elevated expression of the zebrafish orthologues of the mammalian pro-inflammatory cytokine genes, Tumour necrosis factor-α, Interleukin-8 and Interferon-γ, and increased neutrophil and macrophage recruitment. This study demonstrates for the first time that the larval zebrafish innate immune response to infection is enhanced during light exposure, suggesting that, similar to mammalian systems, the larval zebrafish response to infection is light-regulated.

How Intraday Index Changes Influence Periodontal Assessment: A Preliminary Study

It is reputed that periodontal indices remain unchanged over a 24-hour period, with great clinical significance. This preliminary study analyzes daily index changes. In 56 selected patients, full-mouth plaque score (FMPS), full-mouth bleeding score (FMBS), periodontal screening and recording (PSR) indices, and periodontal risk assessment (PRA) were recorded at baseline and three times per day (check-I: 08.30, check-II: 11.30, and check-III: 14.30), after appropriate cause-related therapy. Correlation between variables was statistically analyzed by Stata. All periodontal indices improved at the examination phase. Statistical differences were detected for FMPS comparing all thrice daily checks. Statistical differences were detected for FMBS and PRA comparing check-III with check-I and check-II. PSR showed no significant changes. The worst baseline indices produced the widest daily fluctuation at the examination phase. Significant variation of indices is directly related to clinical severity of periodontal conditions at baseline. Patients affected by severe periodontal disease may show significantly greater index changes. As indices are routinely recorded only once per day, the index daily variation has clinical significance. This greatly affects therapeutic strategy as correct periodontal assessment requires multiple evaluations at standardized times, particularly when baseline conditions are severe.

Endogenous melatonin promotes rhythmic recruitment of neutrophils toward an injury in zebrafish

Neutrophil recruitment to injured tissue appears to be an evolutionarily conserved strategy for organisms to fight against exogenous insults. Recent studies have shown rhythmic migration of neutrophils and several factors, including melatonin, have been implicated in regulating this rhythmic migration. The mechanisms underlying how endogenous melatonin regulates rhythmic neutrophils migration, however, are unclear. Here we generated a zebrafish annat2 mutant that lacks endogenous melatonin and, subsequently, a Tg(lyz:EGFP);aanat2^−/− transgenic line that allows for monitoring neutrophils migration visually in live zebrafish. We observed that migrating neutrophils are significantly reduced in aanat2^−/− mutant zebrafish under a light/dark condition, and the disrupted migrating rhythmicity of neutrophils in aanat2^−/− zebrafish is independent of the circadian clock. Further, we also found that endogenous melatonin enhances neutrophils migration likely by inducing the expression of cytokines such as interleukin-8 and interleukin-1β. Together, our findings provide evidence that endogenous melatonin promotes rhythmic migration of neutrophils through cytokines in zebrafish.

Immunity around the clock

Immunity is a high-cost, high-benefit trait that defends against pathogens and noxious stimuli but whose overactivation can result in immunopathologies and sometimes even death. Because many immune parameters oscillate rhythmically with the time of day, the circadian clock has emerged as an important gatekeeper for reducing immunity-associated costs, which, in turn, enhances organismal fitness. This is mediated by interactions between extrinsic environmental cues and the intrinsic oscillators of immune cells, which together optimize immune responses throughout the circadian cycle. The elucidation of these clock-controlled immunomodulatory mechanisms might uncover new approaches for treating infections and chronic inflammatory diseases.

Impact of operation timing on post-operative infections following colorectal cancer surgery

BACKGROUND

To investigate the impact of operation timing on post-operative infections in a cohort of patients undergoing colorectal cancer surgery.

METHODS

We prospectively analysed surgical outcomes in patients who underwent colorectal cancer surgery at the First Affiliated Hospital, College of Medicine, Zhejiang University, from January to December in 2014. In this non-randomized trial, patients were divided into three groups according to the surgery start time: CT1 (07:00 to 12:00 h), CT2 (12:01 to 18:00 h), and CT3 (18:01 h to midnight). The primary outcome was the proportion of patients developing infections within 4 weeks of the surgical procedure.

RESULTS

Out of 756 patients that were enrolled in the study, 118 developed post-operative infections. The results from blood and pus culture showed 97.1% specimen as being pathogen-free. The overall incidence of post-operative infection was 14.5% (38 of 262), 15.3% (46 of 300) and 17.5% (34 of 194) in the CT1, CT2 and CT3 group, respectively, with no significant inter-group differences. However, white blood cell counts, C-reactive protein and glucose levels at 24 h after the surgical procedure showed significant differences between the three groups (one-way ANOVA, P < 0.05).

CONCLUSION

The occurrence of post-operative infection in patients undergoing colorectal cancer surgery was not associated with operation timing. The expression of several inflammatory markers, such as white blood cell counts, C-reactive protein and blood glucose levels tended to correlate with the surgery start time.

A matter of time: study of circadian clocks and their role in inflammation

Circadian rhythms regulate changes in physiology, allowing organisms to respond to predictable environmental demands varying over a 24 h period. A growing body of evidence supports a key role for the circadian clock in the regulation of immune functions and inflammatory responses, which influence the understanding of infections and inflammatory diseases and their treatment. A variety of experimental methods have been used to assess the complex bidirectional crosstalk between the circadian clock and inflammation. In this review, we summarize the organization of the molecular clock, experimental methods used to study circadian rhythms, and both the inflammatory and immune consequences of circadian disturbance.

Endogenous circadian regulation of pro-inflammatory cytokines and chemokines in the presence of bacterial lipopolysaccharide in humans

Various aspects of immune response exhibit 24-h variations suggesting that infection susceptibility and treatment efficacy may vary by time of day. Whether these 24-h variations are endogenous or evoked by changes in environmental or behavioral conditions is not known. We assessed the endogenous circadian control and environmental and behavioral influences on ex-vivo lipopolysaccharide stimulation of whole blood in thirteen healthy participants under 48h of baseline conditions with standard sleep-wake schedules and 40-50h of constant environmental and behavioral (constant routine; CR) conditions. Significant 24-h rhythms were observed under baseline conditions in Monocyte Chemotactic Protein, Granulocyte-Macrophage Colony-Stimulating Factor and Interleukin 8 but not Tumor Necrosis Factor alpha whereas significant 24-h rhythms were observed in all four immune factors under CR conditions. The rhythm amplitudes, expressed as a percentage of mean, were comparable between immune factors and across conditions. In contrast, the acrophase time (time of the fitted peak) was different between immune factors, and included daytime and nighttime peaks and changes across behavioral conditions. These results suggest that the endogenous circadian system underpins the temporal organization of immune responses in humans with additional effects of external environmental and behavioral cycles. These findings have implications for understanding the adverse effects of recurrent circadian disruption and sleep curtailment on immune function.

Circadian control of innate immunity in macrophages by miR-155 targeting Bmal1

The response to an innate immune challenge is conditioned by the time of day, but the molecular basis for this remains unclear. In myeloid cells, there is a temporal regulation to induction by lipopolysaccharide (LPS) of the proinflammatory microRNA miR-155 that correlates inversely with levels of BMAL1. BMAL1 in the myeloid lineage inhibits activation of NF-κB and miR-155 induction and protects mice from LPS-induced sepsis. Bmal1 has two miR-155-binding sites in its 3'-UTR, and, in response to LPS, miR-155 binds to these two target sites, leading to suppression of Bmal1 mRNA and protein in mice and humans. miR-155 deletion perturbs circadian function, gives rise to a shorter circadian day, and ablates the circadian effect on cytokine responses to LPS. Thus, the molecular clock controls miR-155 induction that can repress BMAL1 directly. This leads to an innate immune response that is variably responsive to challenges across the circadian day.

Widespread seasonal gene expression reveals annual differences in human immunity and physiology

Seasonal variations are rarely considered a contributing component to human tissue function or health, although many diseases and physiological process display annual periodicities. Here we find more than 4,000 protein-coding mRNAs in white blood cells and adipose tissue to have seasonal expression profiles, with inverted patterns observed between Europe and Oceania. We also find the cellular composition of blood to vary by season, and these changes, which differ between the United Kingdom and The Gambia, could explain the gene expression periodicity. With regards to tissue function, the immune system has a profound pro-inflammatory transcriptomic profile during European winter, with increased levels of soluble IL-6 receptor and C-reactive protein, risk biomarkers for cardiovascular, psychiatric and autoimmune diseases that have peak incidences in winter. Circannual rhythms thus require further exploration as contributors to various aspects of human physiology and disease.

The influence of biological rhythms on host-parasite interactions

Biological rhythms, from circadian control of cellular processes to annual cycles in life history, are a main structural element of biology. Biological rhythms are considered adaptive because they enable organisms to partition activities to cope with, and take advantage of, predictable fluctuations in environmental conditions. A flourishing area of immunology is uncovering rhythms in the immune system of animals, including humans. Given the temporal structure of immunity, and rhythms in parasite activity and disease incidence, we propose that the intersection of chronobiology, disease ecology, and evolutionary biology holds the key to understanding host-parasite interactions. Here, we review host-parasite interactions while explicitly considering biological rhythms, and propose that rhythms: influence within-host infection dynamics and transmission between hosts, might account for diel and annual periodicity in host-parasite systems, and can lead to a host-parasite arms race in the temporal domain.

Circadian Clocks in the Immune System

The immune system is a complex set of physiological mechanisms whose general aim is to defend the organism against non-self-bodies, such as pathogens (bacteria, viruses, parasites), as well as cancer cells. Circadian rhythms are endogenous 24-h variations found in virtually all physiological processes. These circadian rhythms are generated by circadian clocks, located in most cell types, including cells of the immune system. This review presents an overview of the clocks in the immune system and of the circadian regulation of the function of immune cells. Most immune cells express circadian clock genes and present a wide array of genes expressed with a 24-h rhythm. This has profound impacts on cellular functions, including a daily rhythm in the synthesis and release of cytokines, chemokines and cytolytic factors, the daily gating of the response occurring through pattern recognition receptors, circadian rhythms of cellular functions such as phagocytosis, migration to inflamed or infected tissue, cytolytic activity, and proliferative response to antigens. Consequently, alterations of circadian rhythms (e.g., clock gene mutation in mice or environmental disruption similar to shift work) lead to disturbed immune responses. We discuss the implications of these data for human health and the areas that future research should aim to address.

An epithelial circadian clock controls pulmonary inflammation and glucocorticoid action

The circadian system is an important regulator of immune function. Human inflammatory lung diseases frequently show time-of-day variation in symptom severity and lung function, but the mechanisms and cell types underlying these effects remain unclear. We show that pulmonary antibacterial responses are modulated by a circadian clock within epithelial club (Clara) cells. These drive circadian neutrophil recruitment to the lung via the chemokine CXCL5. Genetic ablation of the clock gene Bmal1 (also called Arntl or MOP3) in bronchiolar cells disrupts rhythmic Cxcl5 expression, resulting in exaggerated inflammatory responses to lipopolysaccharide and an impaired host response to Streptococcus pneumoniae infection. Adrenalectomy blocks rhythmic inflammatory responses and the circadian regulation of CXCL5, suggesting a key role for the adrenal axis in driving CXCL5 expression and pulmonary neutrophil recruitment. Glucocorticoid receptor occupancy at the Cxcl5 locus shows circadian oscillations, but this is disrupted in mice with bronchiole-specific ablation of Bmal1, leading to enhanced CXCL5 expression despite normal corticosteroid secretion. The therapeutic effects of the synthetic glucocorticoid dexamethasone depend on intact clock function in the airway. We now define a regulatory mechanism that links the circadian clock and glucocorticoid hormones to control both time-of-day variation and the magnitude of pulmonary inflammation and responses to bacterial infection.

Circadian clock proteins and immunity

Immune parameters change with time of day and disruption of circadian rhythms has been linked to inflammatory pathologies. A circadian-clock-controlled immune system might allow an organism to anticipate daily changes in activity and feeding and the associated risk of infection or tissue damage to the host. Responses to bacteria have been shown to vary depending on time of infection, with mice being more at risk of sepsis when challenged ahead of their activity phase. Studies highlight the extent to which the molecular clock, most notably the core clock proteins BMAL1, CLOCK, and REV-ERBα, control fundamental aspects of the immune response. Examples include the BMAL1:CLOCK heterodimer regulating toll-like receptor 9 (TLR9) expression and repressing expression of the inflammatory monocyte chemokine ligand (CCL2) as well as REV-ERBα suppressing the induction of interleukin-6. Understanding the daily rhythm of the immune system could have implications for vaccinations and how we manage infectious and inflammatory diseases.

Environmental circadian disruption elevates the IL-6 response to lipopolysaccharide in blood

The immune system is regulated by circadian clocks within the brain and immune cells. Environmental circadian disruption (ECD), consisting of a 6-h phase advance of the light:dark cycle once a week for 4 weeks, elevates the inflammatory response to lipopolysaccharide (LPS) both in vivo and in vitro. This indicates that circadian disruption adversely affects immune function; however, it remains unclear how the circadian system regulates this response under ECD conditions. Here, we develop an assay using ex vivo whole-blood LPS challenge to investigate the circadian regulation of immune responses in mice and to determine the effects of ECD on these rhythms. LPS-induced IL-6 release in whole blood was regulated in a circadian manner, peaking during subjective day under both entrained and free-running conditions. This LPS-induced IL-6 release rhythm was associated with daily variation in both white blood cell counts and immune cell responsiveness. ECD increased the overall level of LPS-induced IL-6 release by increasing immune cell responsiveness and not by affecting immune cell number or the circadian regulation of this rhythm. This indicates that ECD produces pathological immune responses by increasing the proinflammatory responses of immune cells. Also, this newly developed whole blood assay can provide a noninvasive longitudinal method to quantify potential health consequences of circadian disruption in humans.

Circadian gene Bmal1 regulates diurnal oscillations of Ly6C(hi) inflammatory monocytes

Circadian clocks have evolved to regulate physiologic and behavioral rhythms in anticipation of changes in the environment. Although the molecular clock is present in innate immune cells, its role in monocyte homeostasis remains unknown. Here, we report that Ly6C(hi) inflammatory monocytes exhibit diurnal variation, which controls their trafficking to sites of inflammation. This cyclic pattern of trafficking confers protection against Listeria monocytogenes and is regulated by the repressive activity of the circadian gene Bmal1. Accordingly, myeloid cell-specific deletion of Bmal1 induces expression of monocyte-attracting chemokines and disrupts rhythmic cycling of Ly6C(hi) monocytes, predisposing mice to development of pathologies associated with acute and chronic inflammation. These findings have unveiled a critical role for BMAL1 in controlling the diurnal rhythms in Ly6C(hi) monocyte numbers.

Circadian control of the immune system

Circadian rhythms, which have long been known to play crucial roles in physiology, are emerging as important regulators of specific immune functions. Circadian oscillations of immune mediators coincide with the activity of the immune system, possibly allowing the host to anticipate and handle microbial threats more efficiently. These oscillations may also help to promote tissue recovery and the clearance of potentially harmful cellular elements from the circulation. This Review summarizes the current knowledge of circadian rhythms in the immune system and provides an outlook on potential future implications.

Adenosine A2A receptor and TNF-α regulate the circadian machinery of the human monocytic THP-1 cells

Morning stiffness and increased symptoms of inflammatory arthritis are among the most common manifestations of rheumatoid arthritis (RA). Tumor necrosis alpha (TNF-α), an important mediator of inflammation in RA, regulates the circadian expression of clock proteins, and adenosine A(2A) receptors (A(2A)R) mediate many of the anti-inflammatory and antirheumatic actions of methotrexate, the cornerstone drug in the treatment of RA. We found that A(2A)R activation and TNF-α activated the clock core loop of the human monocytic THP-1 cell line. We further observed that interleukin (IL)-10, but not IL-12, mRNA expression fluctuates in a circadian fashion and that TNF-α and A(2A)R stimulation combined increased IL-10 expression. Interestingly, TNF-α, but not CGS21680, dramatically inhibited IL-12 mRNA expression. The demonstration that A(2A)R and TNF-α regulate the intrinsic circadian clock in immune cells provides an explanation for both the pathologic changes in circadian rhythms in RA and for the adverse circadian effects of methotrexate, such as fatigue.

Adrenergic nerves govern circadian leukocyte recruitment to tissues

The multistep sequence leading to leukocyte migration is thought to be locally regulated at the inflammatory site. Here, we show that broad systemic programs involving long-range signals from the sympathetic nervous system (SNS) delivered by adrenergic nerves regulate rhythmic recruitment of leukocytes in tissues. Constitutive leukocyte adhesion and migration in murine bone marrow (BM) and skeletal-muscle microvasculature fluctuated with circadian peak values at night. Migratory oscillations, altered by experimental jet lag, were implemented by perivascular SNS fibers acting on β-adrenoreceptors expressed on nonhematopoietic cells and leading to tissue-specific, differential circadian oscillations in the expression of endothelial cell adhesion molecules and chemokines. We showed that these rhythms have physiological consequences through alteration of hematopoietic cell recruitment and overall survival in models of septic shock, sickle cell vaso-occlusion, and BM transplantation. These data provide unique insights in the leukocyte adhesion cascade and the potential for time-based therapeutics for transplantation and inflammatory diseases.

Circadian variation of the response of T cells to antigen

Circadian clocks regulate many important aspects of physiology, and their disturbance leads to various medical conditions. Circadian variations have been found in immune system variables, including daily rhythms in circulating WBC numbers and serum concentration of cytokines. However, control of immune functional responses by the circadian clock has remained relatively unexplored. In this study, we show that mouse lymph nodes exhibit rhythmic clock gene expression. T cells from lymph nodes collected over 24 h show a circadian variation in proliferation after stimulation via the TCR, which is blunted in Clock gene mutant mice. The tyrosine kinase ZAP70, which is just downstream of the TCR in the T cell activation pathway and crucial for T cell function, exhibits rhythmic protein expression. Lastly, mice immunized with OVA peptide-loaded dendritic cells in the day show a stronger specific T cell response than mice immunized at night. These data reveal circadian control of the Ag-specific immune response and a novel regulatory mode of T cell proliferation, and may provide clues for more efficient vaccination strategies.

A circadian clock in macrophages controls inflammatory immune responses

Time of day-dependent variations of immune system parameters are ubiquitous phenomena in immunology. The circadian clock has been attributed with coordinating these variations on multiple levels; however, their molecular basis is little understood. Here, we systematically investigated the link between the circadian clock and rhythmic immune functions. We show that spleen, lymph nodes, and peritoneal macrophages of mice contain intrinsic circadian clockworks that operate autonomously even ex vivo. These clocks regulate circadian rhythms in inflammatory innate immune functions: Isolated spleen cells stimulated with bacterial endotoxin at different circadian times display circadian rhythms in TNF-alpha and IL-6 secretion. Interestingly, we found that these rhythms are not driven by systemic glucocorticoid variations nor are they due to the detected circadian fluctuation in the cellular constitution of the spleen. Rather, a local circadian clock operative in splenic macrophages likely governs these oscillations as indicated by endotoxin stimulation experiments in rhythmic primary cell cultures. On the molecular level, we show that >8% of the macrophage transcriptome oscillates in a circadian fashion, including many important regulators for pathogen recognition and cytokine secretion. As such, understanding the cross-talk between the circadian clock and the immune system provides insights into the timing mechanism of physiological and pathophysiological immune functions.

Seasonality of invasive pneumococcal disease: temporal relation to documented influenza and respiratory syncytial viral circulation

BACKGROUND

Seasonal fluctuation in the incidence of invasive pneumococcal disease has been attributed to winter virus exposure (e.g., influenza and respiratory syncytial virus [RSV]). Evidence of a direct correlation of invasive pneumococcal disease with laboratory-confirmed virus seasons, however, is limited. Using two prospective surveillance networks, the temporal relation between invasive pneumococcal disease and isolation of circulating winter viruses was explored.

METHODS

Episodes of invasive pneumococcal disease in five Tennessee counties were collected prospectively from January 1995 through June 2002. Virus seasons were defined using prospective laboratory-based surveillance. Correlation between weekly identification of invasive pneumococcal disease and laboratory isolation of RSV and influenza, as well as comparisons of the frequencies of invasive pneumococcal disease episodes during viral and nonviral seasons were determined.

RESULTS

A total of 4147 invasive pneumococcal disease episodes were identified. Weekly frequency of invasive pneumococcal disease correlated directly with the weekly frequency of isolation of RSV (r = 0.56, P <0.001) and influenza (r= 0.40, P <0.001). The average weekly frequency of invasive pneumococcal disease during RSV and influenza seasons was higher than during the nonviral seasons (P <0.001 for each year).

CONCLUSION

Weekly episodes of invasive pneumococcal disease correlated temporally with laboratory-confirmed weekly isolation of RSV and influenza, and the incidence of invasive pneumococcal disease was increased when these viruses were circulating in the community.

Comparison of methods of temperature measurement in swine

The purpose of these experiments was to test the equivalence of pulmonary artery, urinary bladder, tympanic, rectal and femoral artery methods of temperature measurement in healthy and critically ill swine under clinical intensive care unit (ICU) conditions using a prospective, time series design. First, sensors were tested for error and sensitivity to change in temperature with a precision-controlled water bath and a laboratory-certified digital thermometer for temperatures 34-42 degrees C. There was virtually no systematic (bias) or random (precision) error (<0.2 degrees C). The bladder sensor had the slowest response time to change in temperature (105-120 s). Next, testing was done in an experimental porcine ICU in a non-profit research institution with four male, sedated, and mechanically ventilated domestic farm pigs. The in vivo experiments were conducted over periods of 41-168 h with temperatures measured every 1-5 s. The bladder, tympanic and rectal methods had unacceptable bias (>or=0.5 degrees C) and/or precision (>or=0.2 degrees C). Response time varied from 7 s with the femoral artery method to 280 s (4.7 min) with the tympanic method. We concluded that equivalence of the methods was insufficient for them to be used interchangeably in the porcine ICU. Intravascular monitoring of core body temperature produces optimal measurement of porcine temperature under varying conditions of physiological stability.