Influence of circadian clocks on adaptive immunity and vaccination responses.

The adaptive immune response is under circadian control, yet, why adaptive immune reactions continue to exhibit circadian changes over long periods of time is unknown. Using a combination of experimental and mathematical modeling approaches, we show here that dendritic cells migrate from the skin to the draining lymph node in a time-of-day-dependent manner, which provides an enhanced likelihood for functional interactions with T cells. Rhythmic expression of TNF in the draining lymph node enhances BMAL1-controlled ICAM-1 expression in high endothelial venules, resulting in lymphocyte infiltration and lymph node expansion. Lymph node cellularity continues to be different for weeks after the initial time-of-day-dependent challenge, which governs the immune response to vaccinations directed against Hepatitis A virus as well as SARS-CoV-2. In this work, we present a mechanistic understanding of the time-of-day dependent development and maintenance of an adaptive immune response, providing a strategy for using time-of-day to optimize vaccination regimes.

Predictors of incident malnutrition-a nutritionDay analysis in 11,923 nursing home residents.

BACKGROUND/OBJECTIVES: Malnutrition (MN) in nursing home (NH) residents is associated with poor outcome. In order to identify those with a high risk of incident MN, the knowledge of predictors is crucial. Therefore, we investigated predictors of incident MN in older NH-residents. SUBJECTS/METHODS: NH-residents participating in the nutritionDay-project (nD) between 2007 and 2018, aged ≥65 years, with complete data on nutritional status at nD and after 6 months and without MN at nD. The association of 17 variables (general characteristics (n = 3), function (n = 4), nutrition (n = 1), diseases (n = 5) and medication (n = 4)) with incident MN (weight loss ≥ 10% between nD and follow-up (FU) or BMI (kg/m2) < 20 at FU) was analyzed in univariate generalized estimated equation (GEE) models. Significant (p < 0.1) variables were selected for multivariate GEE-analyses. Effect estimates are presented as odds ratios and their respective 99.5%-confidence intervals. RESULTS: Of 11,923 non-malnourished residents, 10.5% developed MN at FU. No intake at lunch (OR 2.79 [1.56-4.98]), a quarter (2.15 [1.56-2.97]) or half of the meal eaten (1.72 [1.40-2.11]) (vs. three-quarter to complete intake), the lowest BMI-quartile (20.0-23.0) (1.86 [1.44-2.40]) (vs. highest (≥29.1)), being between the ages of 85 and 94 years (1.46 [1.05; 2.03]) (vs. the youngest age-group 65-74 years)), severe cognitive impairment (1.38 [1.04; 1.84]) (vs. none) and being immobile (1.28 [1.00-1.62]) (vs. mobile) predicted incident MN in the final model. CONCLUSION: 10.5% of non-malnourished NH-residents develop MN within 6 months. Attention should be paid to high-risk groups, namely residents with poor meal intake, low BMI, severe cognitive impairment, immobility, and older age.

Circadian clocks guide dendritic cells into skin lymphatics.

Migration of leukocytes from the skin to lymph nodes (LNs) via afferent lymphatic vessels (LVs) is pivotal for adaptive immune responses1,2. Circadian rhythms have emerged as important regulators of leukocyte trafficking to LNs via the blood3,4. Here, we demonstrate that dendritic cells (DCs) have a circadian migration pattern into LVs, which peaks during the rest phase in mice. This migration pattern is determined by rhythmic gradients in the expression of the chemokine CCL21 and of adhesion molecules in both mice and humans. Chronopharmacological targeting of the involved factors abrogates circadian migration of DCs. We identify cell-intrinsic circadian oscillations in skin lymphatic endothelial cells (LECs) and DCs that cogovern these rhythms, as their genetic disruption in either cell type ablates circadian trafficking. These observations indicate that circadian clocks control the infiltration of DCs into skin lymphatics, a process that is essential for many adaptive immune responses and relevant for vaccination and immunotherapies.

Binding of Rap1 and Riam to Talin1 Fine-Tune ß2 Integrin Activity During Leukocyte Trafficking.

ß2 integrins mediate key processes during leukocyte trafficking. Upon leukocyte activation, the structurally bent ß2 integrins change their conformation towards an extended, intermediate and eventually high affinity conformation, which mediate slow leukocyte rolling and firm arrest, respectively. Translocation of talin1 to integrin adhesion sites by interactions with the small GTPase Rap1 and the Rap1 effector Riam precede these processes. Using Rap1 binding mutant talin1 and Riam deficient mice we show a strong Riam-dependent T cell homing process to lymph nodes in adoptive transfer experiments and by intravital microscopy. Moreover, neutrophils from compound mutant mice exhibit strongly increased rolling velocities to inflamed cremaster muscle venules compared to single mutants. Using Hoxb8 cell derived neutrophils generated from the mutant mouse strains, we show that both pathways regulate leukocyte rolling and adhesion synergistically by inducing conformational changes of the ß2 integrin ectodomain. Importantly, a simultaneous loss of both pathways results in a rolling phenotype similar to talin1 deficient neutrophils suggesting that ß2 integrin regulation primarily occurs via these two pathways.

Loss of direct adrenergic innervation after peripheral nerve injury causes lymph node expansion through IFN-γ.

Peripheral nerve injury can cause debilitating disease and immune cell-mediated destruction of the affected nerve. While the focus has been on the nerve-regenerative response, the effect of loss of innervation on lymph node function is unclear. Here, we show that the popliteal lymph node (popLN) receives direct neural input from the sciatic nerve and that sciatic denervation causes lymph node expansion. Loss of sympathetic, adrenergic tone induces the expression of IFN-γ in LN CD8 T cells, which is responsible for LN expansion. Surgery-induced IFN-γ expression and expansion can be rescued by ß2 adrenergic receptor agonists but not sensory nerve agonists. These data demonstrate the mechanisms governing the pro-inflammatory effect of loss of direct adrenergic input on lymph node function.

Detection of invasive Trichosporon asahii in patient blood by a fungal PCR array.

Rare invasive fungal infections are increasingly emerging in hosts with predisposing factors such as immunodeficiency. Their timely diagnosis remains difficult, as their clinical picture may initially mimic infections with more common fungal species and species identification may be difficult with routine methods or may require time-consuming subcultures. This often results in ineffective drug administration and fatal outcomes. We report on a patient in their early twenties with mixed cellularity classical Hodgkin lymphoma with a disseminated Trichosporon asahii (T. asahii) infection. Even though pathogen detection and identification was possible via the standard procedure consisting of culture followed by matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF) mass spectrometry, the patient passed away in the course of multi organ failure. Herein, we report on a retrospectively applied experimental diagnostic fungal PCR-analysis used on an EDTA blood sample and consisting of two pan-fungal reactions and seven branch-specific reactions. Regarding invasive T. asahii infection, this PCR array could considerably shorten time to diagnosis and switch to a targeted therapy with triazoles.

Determination of optimal time window for cortical mapping in awake craniotomy: assessment of intraoperative reaction speed.

Currently, there is no known time frame when the patients are the most responsive during awake craniotomy. The aim of this work is therefore to determine when the patient has the shortest reaction time and so to extrapolate the optimal time window for cortical mapping. In this analytic observational study, our group has recorded the reaction times of 35 patients undergoing an awake craniotomy and compared them with the preoperative baseline. The operations were performed according to a "sleep-awake-awake" protocol. Data collection was performed in parallel with standard methods for evaluation of language and cognitive functions. The preoperative reaction times of our patient cohort (average ± SD = 510 ± 124 ms) were significantly shorter than those measured during the operation 786 ± 280 ms, p < .001. A one-factor ANOVA within subjects showed a significant increase in reaction times; p < .001. Post hoc comparisons on a Bonferroni-corrected α-error level of .05 showed significant differences between the reaction speed during the 0-10 min time frame and the preoperative baseline, as well as the intraoperative reaction times during the 20-30 min, 30-40 min, and the t > 40 min time frames. In conclusion, measurement of intraoperative reaction speed seems to be a technically feasible method that is well tolerated by the patients. The intraoperative reaction speed performance was shown to be significantly slower than on the day before the operation. The patients seem to be the slowest directly after extubation and gradually wake up during the awake phase. The poorest wakefulness is demonstrated during the first 20 min after extubation.

Circadian Expression of Migratory Factors Establishes Lineage-Specific Signatures that Guide the Homing of Leukocyte Subsets to Tissues.

The number of leukocytes present in circulation varies throughout the day, reflecting bone marrow output and emigration from blood into tissues. Using an organism-wide circadian screening approach, we detected oscillations in pro-migratory factors that were distinct for specific vascular beds and individual leukocyte subsets. This rhythmic molecular signature governed time-of-day-dependent homing behavior of leukocyte subsets to specific organs. Ablation of BMAL1, a transcription factor central to circadian clock function, in endothelial cells or leukocyte subsets demonstrated that rhythmic recruitment is dependent on both microenvironmental and cell-autonomous oscillations. These oscillatory patterns defined leukocyte trafficking in both homeostasis and inflammation and determined detectable tumor burden in blood cancer models. Rhythms in the expression of pro-migratory factors and migration capacities were preserved in human primary leukocytes. The definition of spatial and temporal expression profiles of pro-migratory factors guiding leukocyte migration patterns to organs provides a resource for the further study of the impact of circadian rhythms in immunity.

Differential requirement of kindlin-3 for T cell progenitor homing to the non-vascularized and vascularized thymus.

The role of integrin-mediated adhesion during T cell progenitor homing to and differentiation within the thymus is ill-defined, mainly due to functional overlap. To circumvent compensation, we disrupted the hematopoietic integrin regulator kindlin-3 in mice and found a progressive thymus atrophy that is primarily caused by an impaired homing capacity of T cell progenitors to the vascularized thymus. Notably, the low shear flow conditions in the vascular system at midgestation allow kindlin-3-deficient fetal liver-derived T cell progenitors to extravasate via pharyngeal vessels and colonize the avascular thymus primordium. Once in the thymus, kindlin-3 promotes intrathymic T cell proliferation by facilitating the integrin-dependent crosstalk with thymic antigen presenting cells, while intrathymic T cell migration, maturation into single positive CD4 and CD8 T cells and release into the circulation proceed without kindlin-3. Thus, kindlin-3 is dispensable for integrin-mediated T cell progenitor adhesion and signalling at low and indispensable at high shear forces.

Control of Leukocyte Trafficking by Stress-Associated Hormones.

Leukocyte migration is a crucial process in both homeostatic and inflammatory conditions. The spatiotemporal distribution of immune cells is balanced between processes of cellular mobilization into the bloodstream, their adhesion to vascular beds and trafficking into tissues. Systemic regulation of leukocyte mobility is achieved by different signals including neuronal and hormonal cues, of which the catecholamines and glucocorticoids have been most extensively studied. These hormones are often associated with a stress response, however they regulate immune cell trafficking also in steady state, with effects dependent upon cell type, location, time-of-day, concentration, and duration of signal. Systemic administration of catecholamines, such as the sympathetic neurotransmitters adrenaline and noradrenaline, increases neutrophil numbers in the bloodstream but has different effects on other leukocyte populations. In contrast, local, endogenous sympathetic tone has been shown to be crucial for dynamic daily changes in adhesion molecule expression in the bone marrow and skeletal muscle, acting as a key signal to the endothelium and stromal cells to regulate immune cell trafficking. Conversely, glucocorticoids are often reported as anti-inflammatory, although recent data shows a more complex role, particularly under steady-state conditions. Endogenous changes in circulating glucocorticoid concentration induce redistribution of cells and potentiate inflammatory responses, and in many paradigms glucocorticoid action is strongly influenced by time of day. In this review, we discuss the current knowledge of catecholamine and glucocorticoid regulation of leukocyte migration under homeostatic and stimulated conditions.

A Systematic and Meta-Analysis of Mortality in Experimental Mouse Models Analyzing Delayed Cerebral Ischemia After Subarachnoid Hemorrhage.

Animal models are established to display the pathophysiological changes following subarachnoid hemorrhage (SAH). The aim of the present study was to determine case fatality in mouse delayed cerebral ischemia (DCI) models, to compare mortality in mouse DCI models to case fatality in human SAH patients, and to identify factors influencing mouse mortality. A systematic search of the PubMed database was performed to identify all studies that assessed mouse DCI models. Mortality rates and predictor variables were extracted and compared to the human case fatality after SAH as previously reported. Predictors for mouse mortality were identified through multivariate analysis. Forty-eight studies were included in the quantitative analysis. The mean overall mortality rate was 21% in mouse DCI models. However, the time period between induction of SAH and evaluation of mortality rates is a significant variable influencing the mortality rate in mouse SAH models. The experimental SAH model was the only significant predictor for mouse mortality after 48 h. In contrast, neither the genetic background nor the anesthetic changed the case fatality rate. Mouse mortality at 24, 48, and 72 h after experimental SAH in DCI models was significantly lower than human case fatality following aneurysmal SAH. The mean overall mortality rate in mouse DCI models is significantly lower than human case fatality following aneurysmal SAH. However, time between SAH induction and evaluation is a significant variable influencing the mortality rate in mouse SAH models. Further analyses will be required to establish whether and to which extent different DCI models affect mortality and reflect human pathophysiology.

Using testing to improve learning after severe traumatic brain injury.

OBJECTIVE: Recent work in cognitive psychology suggests that testing can increase memory for both previously and subsequently studied information. Here we examined whether these beneficial (backward and forward) effects of testing generalize to individuals with severe traumatic brain injury (TBI). METHOD: Twenty-four persons with severe TBI, 12.7 years postinjury, and 12 healthy controls participated in the study. Participants studied three lists of items in anticipation of a final cumulative recall test. They were tested immediately between the study of lists or not. RESULTS: Immediate testing of Lists 1 and 2 enhanced recall of both the previously studied information (Lists 1 and 2) and the subsequently studied information (List 3). The enhancement for the three lists arose for individuals with severe TBI and healthy controls, and did not differ in size between subject groups. CONCLUSION: The findings indicate that TBI persons show a very general benefit from testing, including both backward and forward effects of retrieval practice. Testing thus might be a powerful technique to improve learning and memory in persons with severe TBI.