The role of neutrophil chemotaxis activity as an immunologic biomarker to predict mortality in critically-ill patients with severe sepsis

Microfluidic device reveals new insights into impairment of neutrophil transmigration in patients with sepsis

Neutrophils need to migrate through tight tissue spaces to eliminate pathogens, but their movement is often hindered by their large and stiff nuclei. Neutrophil migration is impaired in sepsis patients, but it is unclear whether this defect is related to the deformability of their nuclei. Herein, we designed microfluidic devices with micron-scale narrow slits to simulate biological barriers. This setup allowed us to observe and record neutrophil movement and nuclear deformation in real-time. We also developed a method for morphological analysis to quantify nucleus deformation in numerous individual cells. Our studies showed that neutrophils from healthy individuals could adjust their nuclear shape to squeeze through these constrictions, whereas those from sepsis patients demonstrated less flexibility. Neutrophils with rigid nuclei struggled to pass through narrow gaps and were more likely to rupture under pressure. These findings suggest that the migration defects of neutrophils observed in sepsis may be attributed to the inability of neutrophils to deform their nuclei, highlighting the crucial role of microfluidic technologies in offering new insights into migration defects under pathological conditions.

Hypothermia or hyperthermia, which is associated with patient outcomes in critically ill children with sepsis? -A retrospective study

OBJECTIVES

In the early stage of sepsis, identifying high-risk paediatric patients with a poor prognosis and providing timely and adequate treatment are critical. This study aimed to evaluate the effect of average body temperature within 24 hours of admission on the short-term prognosis of paediatric patients with sepsis.

DESIGN

A retrospective cohort study.

SETTING

A single-centre, tertiary care hospital in China, containing patient data from 2010 to 2018.

PARTICIPANTS

1144 patients with sepsis were included.

INTERVENTION

None.

PRIMARY AND SECONDARY OUTCOME MEASURES

The main outcome measure was in-hospital mortality, which was defined as death from any cause during hospitalisation. The secondary outcome was the length of hospital stay.

RESULTS

The LOWESS method showed a roughly 'U'-shaped relationship between body temperature on the first day and in-hospital mortality. Multivariate logistic regression showed that severe hypothermia (OR 14.72, 95% CI 4.84 to 44.75), mild hypothermia (OR 3.71, 95% CI 1.26 to 10.90), mild hyperthermia (OR 3.41, 95% CI 1.17 to 9.90) and severe hyperthermia (OR 5.15, 95% CI 1.84 to 14.43) were independent risk factors for in-hospital mortality. Compared with other variables, the Wald χ² value of temperature on the first day minus the degree of freedom was the highest.

CONCLUSIONS

Whether hypothermic or hyperthermic, the more abnormal the temperature on the first day is, the higher the risk of in-hospital death in children with sepsis.

The Regulation of Neutrophil Migration in Patients with Sepsis: The Complexity of the Molecular Mechanisms and Their Modulation in Sepsis and the Heterogeneity of Sepsis Patients

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Common causes include gram-negative and gram-positive bacteria as well as fungi. Neutrophils are among the first cells to arrive at an infection site where they function as important effector cells of the innate immune system and as regulators of the host immune response. The regulation of neutrophil migration is therefore important both for the infection-directed host response and for the development of organ dysfunctions in sepsis. Downregulation of CXCR4/CXCL12 stimulates neutrophil migration from the bone marrow. This is followed by transmigration/extravasation across the endothelial cell barrier at the infection site; this process is directed by adhesion molecules and various chemotactic gradients created by chemotactic cytokines, lipid mediators, bacterial peptides, and peptides from damaged cells. These mechanisms of neutrophil migration are modulated by sepsis, leading to reduced neutrophil migration and even reversed migration that contributes to distant organ failure. The sepsis-induced modulation seems to differ between neutrophil subsets. Furthermore, sepsis patients should be regarded as heterogeneous because neutrophil migration will possibly be further modulated by the infecting microorganisms, antimicrobial treatment, patient age/frailty/sex, other diseases (e.g., hematological malignancies and stem cell transplantation), and the metabolic status. The present review describes molecular mechanisms involved in the regulation of neutrophil migration; how these mechanisms are altered during sepsis; and how bacteria/fungi, antimicrobial treatment, and aging/frailty/comorbidity influence the regulation of neutrophil migration.

Expert consensus on the monitoring and treatment of sepsis-induced immunosuppression

Emerged evidence has indicated that immunosuppression is involved in the occurrence and development of sepsis. To provide clinical practice recommendations on the immune function in sepsis, an expert consensus focusing on the monitoring and treatment of sepsis-induced immunosuppression was developed. Literature related to the immune monitoring and treatment of sepsis were retrieved from PubMed, Web of Science, and Chinese National Knowledge Infrastructure to design items and expert opinions were collected through an online questionnaire. Then, the Delphi method was used to form consensus opinions, and RAND appropriateness method was developed to provide consistency evaluation and recommendation levels for consensus opinions. This consensus achieved satisfactory results through two rounds of questionnaire survey, with 2 statements rated as perfect consistency, 13 as very good consistency, and 9 as good consistency. After summarizing the results, a total of 14 strong recommended opinions, 8 weak recommended opinions and 2 non-recommended opinions were produced. Finally, a face-to-face discussion of the consensus opinions was performed through an online meeting, and all judges unanimously agreed on the content of this consensus. In summary, this expert consensus provides a preliminary guidance for the monitoring and treatment of immunosuppression in patients with sepsis.

Predictors of in-hospital mortality in a cohort of people living with HIV (PLHIV) admitted to an academic medical intensive care unit from 2009 to 2014: A retrospective cohort study

Outcomes for critically ill people living with human immunodeficiency virus (PLHIV) have changed with the use of antiretroviral therapy (ART). To identify these outcomes and correlates of mortality in a contemporary critically ill cohort in an urban academic medical center in Baltimore, a city with a high burden of HIV, we conducted a retrospective cohort study of individuals admitted to a medical intensive care unit (MICU) at a tertiary care center between 2009 and 2014. PLHIV who were at least 18 years of age with an index MICU admission of ≥24 hours during the 5-year study period were included in this analysis. Data were obtained for participants from the time of MICU admission until hospital discharge and up to 180 days after MICU admission. Logistic regression was used to identify independent predictors of hospital mortality. Between June 2009 and June 2014, 318 PLHIV admitted to the MICU met inclusion criteria. Eighty-six percent of the patients were non-Hispanic Blacks. Poorly controlled HIV was very common with 70.2% of patients having a CD4 cell count <200 cells/mm3 within 3 months prior to admission and only 34% of patients having an undetectable HIV viral load. Hospital mortality for the cohort was 17%. In a univariate model, mortality did not differ by demographic variables, CD4 cell count, HIV viral load, or ART use. Regression analysis adjusted by relevant covariates revealed that MICU patients admitted from the hospital ward were 6.4 times more likely to die in hospital than those admitted from emergency department. Other positive predictors were a diagnosis of end-stage liver disease, cardiac arrest, ventilator-dependent respiratory failure, vasopressor requirement, non-Hodgkin lymphoma, and symptomatic cytomegalovirus disease. In conclusion, in this critically ill cohort with HIV infection, most predictors of mortality were not directly related to HIV and were similar to those for the general population.

Advances in Immune Monitoring Approaches for Sepsis-Induced Immunosuppression

Sepsis represents a life-threatening organ dysfunction due to an aberrant host response. Of note is that majority of patients have experienced a severe immune depression during and after sepsis, which is significantly correlated with the occurrence of nosocomial infection and higher risk of in-hospital death. Nevertheless, the clinical sign of sepsis-induced immune paralysis remains highly indetectable and ambiguous. Given that, specific yet robust biomarkers for monitoring the immune functional status of septic patients are of prominent significance in clinical practice. In turn, the stratification of a subgroup of septic patients with an immunosuppressive state will greatly contribute to the implementation of personalized adjuvant immunotherapy. In this review, we comprehensively summarize the mechanism of sepsis-associated immunosuppression at the cellular level and highlight the recent advances in immune monitoring approaches targeting the functional status of both innate and adaptive immune responses.

Multifactorial assessment of neutrophil chemotaxis efficiency from a drop of blood

Following injury and infection, neutrophils are guided to the affected site by chemoattractants released from injured tissues and invading microbes. During this process (chemotaxis), neutrophils must integrate multiple chemical signals, while also responding to physical constraints and prioritizing their directional decisions to generate an efficient immune response. In some clinical conditions, human neutrophils appear to lose the ability to chemotax efficiently, which may contribute both directly and indirectly to disease pathology. Here, a range of microfluidic designs is utilized to test the sensitivity of chemotaxing neutrophils to various perturbations, including binary decision-making in the context of channels with different chemoattractant gradients, hydraulic resistance, and angle of approach. Neutrophil migration in long narrow channels and planar environments is measured. Conditions in which neutrophils are significantly more likely to choose paths with the steepest chemoattractant gradient and the most direct approach angle, and find that migration efficiency across planar chambers is inversely correlated with chamber diameter. By sequential measurement of neutrophil binary decision-making to different chemoattractant gradients, or chemotactic index in sequential planar environments, data supporting a model of biased random walk for neutrophil chemotaxis are presented.

A Novel Microfluidic Device for the Neutrophil Functional Phenotype Analysis: Effects of Glucose and Its Derivatives AGEs

Neutrophil dysfunction is closely related to the pathophysiology of patients with diabetes mellitus, but existing immunoassays are difficult to implement in clinical applications, and neutrophil’s chemotaxis as a functional biomarker for diabetes mellitus prognostic remains largely unexplored. Herein, a novel microfluidic device consisted of four independent test units with four cell docking structures was developed to study the neutrophil chemotaxis, which allowed multiple cell migration observations under a single field of view (FOV) and guaranteed more reliable results. In vitro studies, the chemotaxis of healthy neutrophils to N-Formyl-Met-Leu-Phe (fMLP) gradient (0, 10, 100, and 1000 nM) was concentration-dependent. The distinct promotion or suppression in the chemotaxis of metformin or pravastatin pretreated cells were observed after exposure to 100 nM fMLP gradient, indicating the feasibility and efficiency of this novel microfluidic device for clinically relevant evaluation of neutrophil functional phenotype. Further, the chemotaxis of neutrophils pretreated with 25, 50, or 70 mM of glucose was quantitatively lower than that of the control groups (i.e., 5 mM normal serum level). Neutrophils exposed to highly concentrated advanced glycation end products (AGEs) (0.2, 0.5, or 1.0 μM; 0.13 μM normal serum AGEs level), a product of prolonged hyperglycemia, showed that the higher the AGEs concentration was, the weaker the migration speed became. Specifically, neutrophils exposed to high concentrations of glucose or AGEs also showed a stronger drifting along with the flow, further demonstrating the change of neutrophil chemotaxis. Interestingly, adding the N-benzyl-4-chloro-N-cyclohexylbenzamide (FPS-ZM1) (i.e., high-affinity RAGE inhibitor) into the migration medium with AGEs could hinder the binding between AGEs and AGE receptor (RAGE) located on the neutrophil, thereby keeping the normal chemotaxis of neutrophils than the ones incubated with AGEs alone. These results revealed the negative effects of high concentrations of glucose and AGEs on the neutrophil chemotaxis, suggesting that patients with diabetes should manage serum AGEs and also pay attention to blood glucose indexes. Overall, this novel microfluidic device could significantly characterize the chemotaxis of neutrophils and have the potential to be further improved into a tool for risk stratification of diabetes mellitus.

Endotoxemia and circulating bacteriome in severe COVID-19 patients

BACKGROUND

When severe, COVID-19 shares many clinical features with bacterial sepsis. Yet, secondary bacterial infection is uncommon. However, as epithelium is injured and barrier function is lost, bacterial products entering the circulation might contribute to the pathophysiology of COVID-19.

METHODS

We studied 19 adults, severely ill patients with COVID-19 infection, who were admitted to King Chulalongkorn Memorial Hospital, Bangkok, Thailand, between 13th March and 17th April 2020. Blood samples on days 1, 3, and 7 of enrollment were analyzed for endotoxin activity assay (EAA), (1 → 3)-β-D-glucan (BG), and 16S rRNA gene sequencing to determine the circulating bacteriome.

RESULTS

Of the 19 patients, 13 were in intensive care and 10 patients received mechanical ventilation. We found 8 patients with high EAA (≥ 0.6) and about half of the patients had high serum BG levels which tended to be higher in later in the illness. Although only 1 patient had a positive blood culture, 18 of 19 patients were positive for 16S rRNA gene amplification. Proteobacteria was the most abundant phylum. The diversity of bacterial genera was decreased overtime.

CONCLUSIONS

Bacterial DNA and toxins were discovered in virtually all severely ill COVID-19 pneumonia patients. This raises a previously unrecognized concern for significant contribution of bacterial products in the pathogenesis of this disease.