Early immunoneutralization of calcitonin precursors attenuates the adverse physiologic response to sepsis in pigs

Biomarkers for risk stratification and antibiotic stewardship in elderly patients

PURPOSE

Optimal treatment of infections in the elderly patients population is challenging because clinical symptoms and signs may be less specific potentially resulting in both, over- and undertreatment. Elderly patients also have a less pronounced immune response to infection, which may influence kinetics of biomarkers of infection.

METHODS

Within a group of experts, we critically reviewed the current literature regarding biomarkers for risk stratification and antibiotic stewardship in elderly patients with emphasis on procalcitonin (PCT).

RESULTS

The expert group agreed that there is strong evidence that the elderly patient population is particularly vulnerable for infections and due to ambiguity of clinical signs and parameters in the elderly, there is considerable risk for undertreatment. At the same time, however, this group of patients is particularly vulnerable for off-target effects from antibiotic treatment and limiting the use of antibiotics is therefore important. The use of infection markers including PCT to guide individual treatment decisions has thus particular appeal in geriatric patients. For the elderly, there is evidence that PCT is a valuable biomarker for assessing the risk of septic complications and adverse outcomes, and helpful for guiding individual decisions for or against antibiotic treatment. There is need for additional educational efforts regarding the concept of "biomarker-guided antibiotic stewardship" for health care providers caring for elderly patients.

CONCLUSION

Use of biomarkers, most notably PCT, has high potential to improve the antibiotic management of elderly patients with possible infection for improving both, undertreatment and overtreatment. Within this narrative review, we aim to provide evidence-based concepts for the safe and efficient use of PCT in elderly patients.

Procalcitonin and Adrenomedullin in Infectious Diseases

Calcitonin (CT) and adrenomedullin (ADM) are members of the CT family. Procalcitonin (PCT) is a prohormone of CT. Elevations in serum PCT and ADM levels are associated with severe sepsis and coronavirus disease 2019 (COVID-19). PCT enhances sepsis mortality and it binds to the CGRP receptor, which is a heterodimer of CT receptor-like receptor and receptor activity-modifying protein 1. The N-terminal truncated form of PCT, PCT3-116, is produced by the cleavage of PCT by dipeptidyl peptidase 4 (DPP-4) and is the main form of PCT in serum during sepsis, inducing microvascular permeability. Mid-regional pro-adrenomedullin (MR-proADM) is used instead of ADM as a biological indicator because ADM is rapidly degraded, and MR-proADM is released at the same rate as ADM. ADM reduces endothelial permeability and promotes endothelial stability. Endothelial dysfunction is responsible for multiple organ failure in sepsis and COVID-19 patients. Therefore, ADM may be an important molecule for improving the severity associated with sepsis and COVID-19. This review focuses on the current knowledge of PCT and ADM in sepsis and COVID-19.

Biomarkers of sepsis in pigs, horses and cattle: from acute phase proteins to procalcitonin

Sepsis is a complex clinical syndrome triggered by an inflammatory host response to an infection. It is usually complicated to detect and diagnose, and has severe consequences in human and veterinary health, especially when treatment is not started early. Therefore, efforts to detect sepsis accurately are needed. In addition, its proper diagnosis could reduce the misuse of antibiotics, which is essential fighting against antimicrobial resistance. This case is a particular issue in farm animals, as antibiotics have been traditionally given massively, but now they are becoming increasingly restricted. When sepsis is suspected in animals, the most frequently used biomarkers are acute phase proteins such as C-reactive protein, serum amyloid A and haptoglobin, but their concentrations can increase in other inflammatory conditions. In human patients, the most promising biomarkers to detect sepsis are currently procalcitonin and presepsin, and there is a wide range of other biomarkers under study. However, there is little information on the application of these biomarkers in veterinary species. This review aims to describe the general concepts of sepsis and the current knowledge about the biomarkers of sepsis in pigs, horses, and cattle and to discuss possible advances in the field.

Regulation and Dysregulation of Endothelial Permeability during Systemic Inflammation

Systemic inflammation can be triggered by infection, surgery, trauma or burns. During systemic inflammation, an overshooting immune response induces tissue damage resulting in organ dysfunction and mortality. Endothelial cells make up the inner lining of all blood vessels and are critically involved in maintaining organ integrity by regulating tissue perfusion. Permeability of the endothelial monolayer is strictly controlled and highly organ-specific, forming continuous, fenestrated and discontinuous capillaries that orchestrate the extravasation of fluids, proteins and solutes to maintain organ homeostasis. In the physiological state, the endothelial barrier is maintained by the glycocalyx, extracellular matrix and intercellular junctions including adherens and tight junctions. As endothelial cells are constantly sensing and responding to the extracellular environment, their activation by inflammatory stimuli promotes a loss of endothelial barrier function, which has been identified as a hallmark of systemic inflammation, leading to tissue edema formation and hypotension and thus, is a key contributor to lethal outcomes. In this review, we provide a comprehensive summary of the major players, such as the angiopoietin-Tie2 signaling axis, adrenomedullin and vascular endothelial (VE-) cadherin, that substantially contribute to the regulation and dysregulation of endothelial permeability during systemic inflammation and elucidate treatment strategies targeting the preservation of vascular integrity.

Targeting Procalcitonin Protects Vascular Barrier Integrity

RATIONALE

Capillary leakage frequently occurs during sepsis and after major surgery and is associated with microvascular dysfunction and adverse outcome. Procalcitonin is a well-established biomarker in inflammation without known impact on vascular integrity.

OBJECTIVE

We determined how procalcitonin induces endothelial hyperpermeability and how targeting procalcitonin protects vascular barrier integrity.

METHODS

In a prospective observational clinical study, procalcitonin levels were assessed in 50 cardiac surgery patients and correlated to postoperative fluid and vasopressor requirements along with sublingual microvascular functionality. Effects of the procalcitonin signaling pathway on endothelial barrier and adherens junctional integrity were characterized in vitro and verified in mice. Inhibition of procalcitonin activation by dipeptidyl-peptidase 4 (DPP4) was evaluated in murine polymicrobial sepsis and clinically verified in cardiac surgery patients chronically taking the DPP4 inhibitor sitagliptin.

MEASUREMENTS AND MAIN RESULTS

Elevated postoperative procalcitonin levels identified patients with 2-fold increased fluid requirements (P<0.01), 1.8-fold higher vasopressor demand (P<0.05) and compromised microcirculation (reduction to 63.5±2.8% of perfused vessels, P<0.05). Procalcitonin induced 1.4-fold endothelial and 2.3-fold pulmonary capillary permeability (both P<0.001) by destabilizing VE-cadherin. Procalcitonin effects were dependent on activation by DPP4 and targeting the procalcitonin receptor or DPP4 during sepsis-induced hyperprocalcitonemia reduced capillary leakage by 54±10.1% and 60.4±6.9% (both P<0.01), respectively. Sitagliptin prior to cardiac surgery was associated with augmented microcirculation (74.1±1.7% vs. 68.6±1.9% perfused vessels in sitagliptin non-medicated patients, P<0.05) and 2.3-fold decreased fluid (P<0.05) and 1.8-fold reduced vasopressor demand postoperatively (P<0.05).

CONCLUSION

Targeting procalcitonin's action on the endothelium is a feasible means to preserve vascular integrity during systemic inflammation associated with hyperprocalcitonemia.

Measurement of procalcitonin in saliva of pigs: a pilot study

Background

Procalcitonin (PCT) is a widely used biomarker of sepsis in human medicine and can have potential applications in the veterinary field. This study aimed to explore whether PCT could be measured in the saliva of pigs and whether its concentration changes in sepsis. Therefore, a specific assay was developed and analytically validated, and changes in PCT concentration were evaluated in two conditions: a) in an experimental model of sepsis produced by the administration of lipopolysaccharide (LPS) to pigs (n = 5), that was compared with a model of non-septic inflammation induced by turpentine oil (n = 4), and b) in healthy piglets (n = 11) compared to piglets with meningitis (n = 20), a disease that usually involves sepsis and whose treatment often requires large amounts of antibiotics in farms.

Results

The assay showed coefficients of variation within the recommended limits and adequate linearity after serial sample dilutions. The method's detection limit was set at 68 μg/L, and the lower limit of quantification was 414 μg/L. In the LPS experiment, higher concentrations of PCT were found after 24 h in the animals injected with LPS (mean = 5790 μg/L) compared to those treated with turpentine oil (mean = 2127 μg/L, P = 0.045). Also, animals with meningitis had higher concentrations of PCT (mean = 21515 μg/L) than healthy pigs (mean = 6096 μg/L, P value < 0.0001).

Conclusions

According to these results, this assay could be potentially used as a tool for the non-invasive detection of sepsis in pigs, which is currently a topic of high importance due to antibiotic use restriction.

Large animal models for translational research in acute kidney injury

While extensive research using animal models has improved the understanding of acute kidney injury (AKI), this knowledge has not been translated into effective treatments. Many promising interventions for AKI identified in mice and rats have not been validated in subsequent clinical trials. As a result, the mortality rate of AKI patients remains high. Inflammation plays a fundamental role in the pathogenesis of AKI, and one reason for the failure to translate promising therapeutics may lie in the profound difference between the immune systems of rodents and humans. The immune systems of large animals such as swine, nonhuman primates, sheep, dogs and cats, more closely resemble the human immune system. Therefore, in the absence of a basic understanding of the pathophysiology of human AKI, large animals are attractive models to test novel interventions. However, there is a lack of reviews on large animal models for AKI in the literature. In this review, we will first highlight differences in innate and adaptive immunities among rodents, large animals, and humans in relation to AKI. After illustrating the potential merits of large animals in testing therapies for AKI, we will summarize the current state of the evidence in terms of what therapeutics have been tested in large animal models. The aim of this review is not to suggest that murine models are not valid to study AKI. Instead, our objective is to demonstrate that large animal models can serve as valuable and complementary tools in translating potential therapeutics into clinical practice.

A risk score based on procalcitonin for predicting acute kidney injury in COVID-19 patients

Background

Acute kidney injury (AKI) has been reported developing commonly in coronavirus disease 2019 (COVID‐19) patients and could increase the risk of poor outcomes in these patients. We design this study to explore the value of serum procalcitonin (PCT) on predicting AKI and construct risk score for predicting AKI in COVID‐19 patients.

Methods

Patients diagnosed with COVID‐19 and hospitalized in Renmin Hospital of Wuhan University between January 30 and February 24, 2020, were included. The least absolute shrinkage and selection operator (LASSO) regression was performed to identify the strongest predictors of AKI. Multivariate logistic regression analysis was conducted to find independent risk factors for AKI and construct risk score using odds ratio (OR) value of those risk factors. Receiver operating characteristics (ROC) curves were plotted, and area under the ROC curve (AUC) value was calculated to evaluate the predictive value of single PCT level and the constructed risk score.

Results

Among 389 included COVID‐19 patients, 28 (7.2%) patients developed AKI. LASSO regression showed hypertension, saturation of arterial oxygen (SaO₂), PCT, and blood urea nitrogen (BUN) were the strongest predictors for AKI. After multivariate logistic regression analysis, only SaO₂ (<0.001), PCT (p = 0.004), and BUN (p = 0.005) were independently associated with development of AKI in COVID‐19 patients. The AUC of single PCT and constructed risk score was 0. 881 and 0.928, respectively.

Conclusion

PCT level is correlated with AKI in COVID‐19 patients. The efficient risk score consisted of SaO₂, PCT, and BUN is readily accessible for physicians to evaluate the possibility of AKI in COVID‐19 patients.

Serum Procalcitonin Level Predicts Acute Kidney Injury After Traumatic Brain Injury

BACKGROUND

A common non-neurologic complication after traumatic brain injury (TBI), acute kidney injury (AKI) is a risk factor of mortality. Some studies confirmed the predictive value of procalcitonin (PCT) on AKI in several clinical settings. We designed this study to explore the predictive value of PCT on AKI after TBI.

METHODS

We retrospectively enrolled patients with TBI admitted to our hospital from February 2015 to June 2019. Multivariate logistic regression analysis was performed to find the risk factors of AKI and construct a predictive model for AKI. Receiver operating characteristics curves were drawn to compare the predictive value of PCT and the constructed model.

RESULTS

A total of 214 patients were included in this study. The incidence of AKI after TBI was 25.70% in this study. Compared with the non-AKI group, the AKI group had higher age (P = 0.031), lower Glasgow Coma Scale (P < 0.001), and higher incidence of coagulopathy (P < 0.001) and shock (P < 0.001). Moreover, patients complicated with AKI had higher in-hospital mortality (P < 0.001) and worse 90-day outcome (P < 0.001). Multivariate logistic regression analysis indicated that age (P = 0.033), PCT (P = 0.002), serum chlorine (P = 0.011), and creatinine (P < 0.001) were independent risk factors of AKI. We constructed a predictive model using these 4 risk factors. The area under receiver operating characteristics curves of the predictive model was 0.928, which was significantly higher than that of a single PCT value (area under receiver operating characteristics curves = 0.833) (Z = 2.395, P < 0.05).

CONCLUSIONS

PCT is valuable in predicting AKI after TBI. To avoid AKI after TBI, physicians can adjust treatment strategies according to the level of PCT.

Overview of procalcitonin in pregnancy and in pre-eclampsia

Procalcitonin (PCT), a precursor for calcitonin, is a prohormone involved in the inflammatory processes, which has been poorly studied in the context of pregnancy. During severe inflammation, PCT derives from almost all cell types, including monocytes and parenchymal tissues, making it a good predictive and diagnostic marker of an inflammatory state with rapidly increased serum levels in inflammation or sepsis. In normal pregnancy, PCT is basally expressed at very low level by decidual cells, even if decidual macrophages, which in normal pregnancy are skewed to M2 macrophages, are resistant to lipopolysaccharide (LPS)-induced production of PCT. As PCT increase is associated with an inflammatory state, several research groups investigated whether PCT can be considered a marker of pre-eclampsia, a pregnancy disease characterized by systemic inflammation. The first aim of this review is to summarize what is already known about the tissues synthesizing PCT, about the stimuli that cause the increase of circulating PCT levels and how PCT acts as a proinflammatory stimulus by itself. Secondly, we will describe the role of this prohormone in normal pregnancy and in pregnancies complicated by pre-eclampsia, highlighting the involvement of the decidual macrophages and the proinflammatory cytokine tumor necrosis factor-α in the modulation of PCT expression in the decidual microenvironment.

Clinical value of procalcitonin for suspected nosocomial bloodstream infection

BACKGROUND/AIMS

Procalcitonin (PCT) may prove to be a useful marker to exclude or predict bloodstream infection (BSI). However, the ability of PCT levels to differentiate BSI from non-BSI episodes has not been evaluated in nosocomial BSI.

METHODS

We retrospectively reviewed the medical records of patients ≥ 18 years of age with suspected BSI that developed more than 48 hours after admission.

RESULTS

Of the 785 included patients, 105 (13.4%) had BSI episodes and 680 (86.6%) had non-BSI episodes. The median serum PCT level was elevated in patients with BSI as compared with those without BSI (0.65 ng/mL vs. 0.22 ng/mL, p = 0.001). The optimal PCT cut-off value of BSI was 0.27 ng/mL, with a corresponding sensitivity of 74.6% (95% confidence interval [CI], 66.4% to 81.7%) and a specificity of 56.5% (95% CI, 52.7% to 60.2%). The area under curve of PCT (0.692) was significantly larger than that of C-reactive protein (CRP; 0.526) or white blood cell (WBC) count (0.518). However, at the optimal cut-off value, PCT failed to predict BSI in 28 of 105 cases (26.7%). The PCT level was significantly higher in patients with an eGFR < 60 mL/min/1.73 m² than in those with an eGFR ≥ 60 mL/min/1.73 m² (0.68 vs. 0.17, p = 0.01).

CONCLUSIONS

PCT was more useful for predicting nosocomial BSI than CRP or WBC count. However, the diagnostic accuracy of predicting BSI remains inadequate. Thus, PCT is not recommended as a single diagnostic tool to avoid taking blood cultures in the nosocomial setting.

Procalcitonin Impairs Endothelial Cell Function and Viability

BACKGROUND

Procalcitonin is used as a diagnostic tool for the identification and risk stratification of septic patients. Procalcitonin plasma concentrations tightly correlate with the severity of the ongoing inflammatory reaction and can rise up to 10,000-fold. Impairment of endothelial cell function plays an important role in the pathogenesis of hypotension and disturbed organ perfusion during sepsis. We investigated the possible effects of procalcitonin itself on endothelial cell function and viability.

METHODS

Human endothelial cells were exposed to 0.01 to 100 ng/mL procalcitonin and investigated for endothelial permeability using transwells, migration in a scratch wound assay and new capillary formation on extracellular matrix in vitro. Tumor necrosis factor-α and vascular endothelial growth factor served as positive controls. Procalcitonin's impact on the response of endothelial cells toward ischemia was investigated in vivo in the murine model of unilateral femoral artery ligation. Procalcitonin-exposed endothelial cells were subjected to immunoblot for the investigation of vascular endothelial-cadherin expression and angiogenic signaling pathways. Flow cytometry was used for the detection of inflammatory activation and viability, and genomic analysis was performed. Data are presented as difference in means and 95% confidence intervals; statistical analyses were performed using analysis of variance/Bonferroni, and P values are reported as adjusted for multiple comparisons (Padjust).

RESULTS

Tumor necrosis factor-α and 0.1 ng/mL procalcitonin induced endothelial barrier disruption after incubation of endothelial monolayers for 6 hours (-2.53 [-4.16 to -0.89], P = .0008 and -2.09 [-3.73 to -0.45], Padjust = .0064 compared with vehicle-treated control, respectively). Procalcitonin beginning at concentrations of 0.02 ng/mL reduced endothelial cell migration (0.26 [0.06 to 0.47], Padjust = .0069) and new capillary formation in vitro (0.47 [0.28 to 0.66], Padjust < .0001) contrasting the proangiogenic action of vascular endothelial growth factor. Left ventricular injection of procalcitonin in mice on postoperative day 1, 3, and 5 after induction of ischemia impaired new capillary formation and recovery of hindlimb perfusion in vivo (number of capillaries/mm in the ischemic leg of vehicle-treated versus procalcitonin-treated mice, 852.6 [383.4-1322], Padjust = .0002). Twenty-four-hour incubation with procalcitonin reduced the expression of vascular endothelial-cadherin at 100 ng/mL (0.39 [0.06-0.71], Padjust = .0167) and induced endothelial cell death (apoptosis, -5.4 [-10.67 to -0.13], Padjust = .0431). No alteration in the expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1 or extracellular signal-regulated kinase 1/2, and AKT signaling pathways was observed. Genomic analysis revealed regulation of a variety of genes involved in inflammation, angiogenesis, and cell growth.

CONCLUSIONS

This study found that procalcitonin itself impaired several aspects of endothelial cell function. Procalcitonin-induced loss of endothelial barrier function may contribute to capillary leakage and therapy-refractory hypotension during sepsis. Anti-angiogenic properties of procalcitonin at low concentrations could also identify procalcitonin as a mediator of vascular disease associated with the metabolic syndrome. Future studies are needed to further test procalcitonin as a potential therapeutic target for preserving vascular dysfunction during acute and chronic inflammatory disorders.

Procalcitonin Impairs Liver Cell Viability and Function In Vitro: A Potential New Mechanism of Liver Dysfunction and Failure during Sepsis?

Purpose. Liver dysfunction and failure are severe complications of sepsis and result in poor outcome and increased mortality. The underlying pathologic mechanisms of hepatocyte dysfunction and necrosis during sepsis are only incompletely understood. Here, we investigated whether procalcitonin, a biomarker of sepsis, modulates liver cell function and viability. Materials and Methods. Employing a previously characterized and patented biosensor system evaluating hepatocyte toxicity in vitro, human hepatocellular carcinoma cells (HepG2/C3A) were exposed to 0.01-50 ng/mL procalcitonin for 2 × 72 h and evaluated for proliferation, necrosis, metabolic activity, cellular integrity, microalbumin synthesis, and detoxification capacity. Acetaminophen served as positive control. For further standardization, procalcitonin effects were confirmed in a cellular toxicology assay panel employing L929 fibroblasts. Data were analyzed using ANOVA/Tukey's test. Results. Already at concentrations as low as 0.25 ng/mL, procalcitonin induced HepG2/C3A necrosis (P < 0.05) and reduced metabolic activity, cellular integrity, synthesis, and detoxification capacity (all P < 0.001). Comparable effects were obtained employing L929 fibroblasts. Conclusion. We provide evidence for procalcitonin to directly impair function and viability of human hepatocytes and exert general cytotoxicity in vitro. Therapeutical targeting of procalcitonin could thus display a novel approach to reduce incidence of liver dysfunction and failure during sepsis and lower morbidity and mortality of septic patients.

Procalcitonin as a biomarker in equine chronic pneumopathies

BACKGROUND

Procalcitonin (PCT), a precursor protein of the hormone calcitonin, is a sensitive inflammatory marker in human medicine, which is primarily used for diagnosis of bacterial sepsis, but is also useful in diagnosis of exacerbation of asthma and COPD. In this study, PCT was evaluated as a potential biomarker for different chronic pneumopathies in the horse using an equine specific ELISA in comparison to established clinical markers and different interleukins. Sixty-four horses were classified as free of respiratory disease, recurrent airway obstruction (RAO), inflammatory airway disease (IAD) or chronic interstitial pneumopathy (CIP) using a scoring system. PCT concentrations were measured in plasma (n = 17) and in the cell-free supernatant of bronchoalveolar lavage (n = 64). PCT concentrations were correlated to interleukins IL-1ß and IL-6 in BALF, clinical findings and BALF cytology.

RESULTS

The median PCT concentrations in plasma were increased in respiratory disease (174.46 ng/ml, n = 7) compared to controls (13.94 ng/ml, n = 10, P = 0.05) and correlated to PCT in BALF supernatant (rs = 0.48). Compared to controls (5.49 ng/ml, n = 15), median PCT concentrations in BALF supernatant correlated to the overall clinical score (rs = 0.32, P = 0.007) and were significantly increased in RAO (13.40 ng/ml, n = 21) and IAD (16.89 ng/ml, n = 16), while no differences were found for CIP (12.02 ng/ml, n = 12). No significant increases were found for IL-1 and IL-6 between controls and respiratory disease in general as well as different disease groups.

CONCLUSIONS

Although some correlations were found between PCT in plasma, BALF supernatant and clinical scores, PCT in BALF does not seem to be a superior marker compared to established clinical markers. PCT in plasma seems to be more promising and a greater number of samples should be evaluated in further studies.

Immunoneutralization of procalcitonin as therapy of sepsis

Prior studies have demonstrated that the prohormone, procalcitonin (ProCT), and its component calcitonin precursors (CTpr) are increased in the serum of septic patients, correlate with the severity of the illness, and persist for relatively long periods of time. Animal studies in septic hamsters have revealed that the administration of ProCT is toxic and that immunoneutralization with IgG that is reactive to this molecule significantly improves survival. A large animal model of a very rapidly lethal polymicrobial sepsis has been developed in the pig in order to measure continuous physiological and metabolic parameters and also to compare the effects in this animal of an immunoneutralization, which is performed late in the course of the disease, to an identical, but early, therapy. Based upon the physiological and metabolic parameters, the late therapy, which was initiated during the fourth hour at a time when pigs were nearly moribund, was found to be as beneficial as early therapy. In both late and early therapy, the only animals to survive at the predetermined time of euthanasia were those which had received immunoneutralization therapy.

Procalcitonin: Is This the Promised Biomarker for Critically Ill Patients?

Objective Procalcitonin (PCT) has been increasingly used in the critical care setting to determine the presence of bacterial infection and also to guide antibiotic therapy. We reviewed PCT's physiologic role, as well as its clinical utility for the management of pediatric critically ill patients. Findings PCT is a precursor of the hormone calcitonin. Its production is induced by inflammatory conditions, especially bacterial infections. Literature shows that PCT is a moderately reliable diagnostic test for severe bacterial infection in children. Synthesis of available adult studies suggests that the use of PCT-based algorithms to support medical decision making reduces antibiotic exposure without compromising safety in critically ill patients. However, no study has addressed the usefulness and safety of PCT to guide antibiotic therapy in severely ill children. In pediatric patients with acute lower respiratory tract infections, the use of PCT-based algorithms also led to a safe decrease in antibiotic treatment duration. Conclusion PCT has demonstrated clinical utility in the pediatric critical care setting when used for the diagnosis of bacterial infections and to guide antibiotic use in children with acute lower respiratory tract infections. However, more research is needed in critically ill children to determine the utility of PCT-driven antibiotic therapy in this population.

Plasma concentrations of copeptin, C-reactive protein and procalcitonin are positively correlated with APACHE II scores in patients with sepsis

OBJECTIVE

To evaluate the correlation between Acute Physiology and Chronic Health Evaluation II (APACHE II) score and plasma concentrations of copeptin, C-reactive protein (CRP) and procalcitonin in patients with sepsis.

METHODS

Patients with sepsis were prospectively enrolled. APACHE II scores were determined during the first 24 h after admission to the intensive care unit. Plasma copeptin, CRP and procalcitonin were quantified at admission, 24 h, 48 h, and 72 h. Survival at 28 days after admission was recorded.

RESULTS

APACHE II score was significantly positively correlated with plasma copeptin, CRP and procalcitonin concentrations. Survivors (n = 15) had significantly lower APACHE II scores and copeptin, CRP and procalcitonin concentrations than nonsurvivors (n = 26). APACHE II score, copeptin at 72 h, CRP at 48 h and procalcitonin at 24 h were independent risk factors for death.

CONCLUSION

Plasma copeptin, CRP and procalcitonin concentrations were positively correlated with APACHE II score in patients with sepsis, and reflected disease severity.

Sandwich enzyme-linked immunosorbent assay for the quantification of human serum albumin fragment 408-423 in bodily fluids

Urinary levels of human serum albumin (hSA) fragment 408-423 have been proposed to represent an early marker for graft-versus-host disease (GvHD) and chronic kidney diseases. Here, we developed an enzyme-linked immunosorbent assay (ELISA) for the quantification of hSA(408-423). The sandwich ELISA has a detection limit of 0.5ng/ml and is highly specific for hSA(408-423) because it does not cross-react with other albumin fragments or the full-length precursor. This ELISA allows rapid and convenient quantification of hSA(408-423) in bodily fluids, further clarifying the prognostic and diagnostic value of this peptide in GvHD, kidney disease, and other disorders.

Host response biomarkers in sepsis: the role of procalcitonin

Procalcitonin is the prohormone of calcitonin and present in minute quantities in health. However, during infection, its levels rise considerably and are correlated with the severity of the infection. Several assays have been developed for measurement of procalcitonin levels; in this article, we will briefly present the PCT-sensitive Kryptor(®) test (Brahms, Hennigsdorf, Germany), one of the most widely used assays for procalcitonin in recent studies. Many studies have demonstrated the value of procalcitonin levels for diagnosing sepsis and assessing disease severity. Procalcitonin levels have also been successfully used to guide antibiotic administration. However, procalcitonin is not specific for sepsis, and values need to be interpreted in the context of a full clinical examination and the presence of other signs and symptoms of sepsis.

A new ELISA for the quantification of equine procalcitonin in plasma as potential inflammation biomarker in horses

In human medicine, procalcitonin (PCT) is a very common and well-established biomarker for sepsis. Even though sepsis is also a leading cause of death in foals and adult horses, up to now, no data about the role of equine PCT in septic horses has been available. Based on monoclonal antibodies targeted against human PCT, we report here the development of a sandwich ELISA for the quantification of equine PCT in equine plasma samples. The ELISA was characterized for intra- and interassay variance and a working range from 25 to 1,000 ng mL(-1) was defined as within this range; both intra- and interassay variances were below 15 %. The target recovery ranged between 73 and 106 %. The ELISA was used to determine the equine PCT concentration in 24 healthy and 5 septic horses to show the potential for clinical evaluation of equine PCT. Significantly different (P = 0.0006) mean equine PCT concentrations were found for the healthy control group and the sepsis group (47 and 8,450 ng mL(-1)).

Procalcitonin predicts mortality in HIV-infected Ugandan adults with lower respiratory tract infections

BACKGROUND AND OBJECTIVE

In low and middle-income countries where HIV infection is prevalent, identifying patients at high risk of dying from lower respiratory tract infections is challenging and validated prognostic models are lacking. Serum procalcitonin may be a useful prognostic tool in these settings. We sought to determine if elevated serum procalcitonin is associated with increased in-hospital mortality and to combine serum procalcitonin with available clinical characteristics to create a clinically useful prognostic model.

METHODS

We conducted a prospective, nested case-control study of 241 HIV-infected adults admitted to Mulago Hospital in Kampala, Uganda with cough ≥2 weeks in duration. We collected demographic and clinical information, baseline serum for procalcitonin analysis, and followed patients to determine in-hospital mortality.

RESULTS

Serum procalcitonin was a strong and independent predictor of inpatient mortality (aOR = 7.69, p = 0.01, sensitivity = 93%, negative predictive value = 97%). Best subset multivariate analysis identified 3 variables that were combined into a prognostic model to risk stratify patients; these variables included respiratory rate ≥30 breaths/minute (aOR = 2.07, p = 0.11), oxygen saturation <90% (aOR = 3.07, p = 0.02), and serum procalcitonin >0.5 ng/ml (aOR = 7.69, p = 0.01). The predicted probability of inpatient mortality ranged from 1% when no variables were present, to 42% when all variables were present.

CONCLUSIONS

Elevated serum procalcitonin >0.5 ng/ml is an independent predictor of in-hospital mortality. Elevated serum procalcitonin, tachypnea, and hypoxemia may be combined into a prognostic model to identify patients at high risk of dying in the hospital. This model may be used to estimate the probability of death and to guide triage and treatment decisions.

Procalcitonin levels predict acute kidney injury and prognosis in acute pancreatitis: a prospective study

Background

Acute kidney injury (AKI) has been proposed as a leading cause of mortality for acute pancreatitis (AP) patients admitted to the intensive care unit (ICU). This study investigated the predictive value of procalcitonin (PCT) for AKI development and relevant prognosis in patients with AP, and compared PCT’s predictive power with that of other inflammation-related variables.

Methods

Between January 2011 and March 2013, we enrolled 305 cases with acute pancreatitis admitted to ICU. Serum levels of PCT, serum amyloid A (SAA), interleukin-6 (IL-6), and C reactive protein (CRP) were determined on admission. Serum PCT was tested in patients who developed AKI on the day of AKI occurrence and on either day 28 after occurrence (for survivors) or on the day of death (for those who died within 28 days).

Results

Serum PCT levels were 100-fold higher in the AKI group than in the non-AKI group on the day of ICU admission (p<0.05). The area under the receiver-operating characteristic (ROC) curve of PCT for predicting AKI was 0.986, which was superior to SAA, CRP, and IL-6 (p<0.05). ROC analysis revealed all variables tested had lower predictive performance for AKI prognosis. The average serum PCT level on day 28 (2.67 (0.89, 7.99) ng/ml) was significantly (p<0.0001) lower than on the day of AKI occurrence (43.71 (19.24,65.69) ng/ml) in survivors, but the serum PCT level on death (63.73 (34.22,94.30) ng/ml) was higher than on the day of AKI occurrence (37.55 (18.70,74.12) ng/ml) in non-survivors, although there was no significant difference between the two days in the latter group (p = 0.1365).

Conclusion

Serum PCT is superior to CRP, IL-6, and SAA for predicting the development of AKI in patients with AP, and also can be used for dynamic evaluation of AKI prognosis.

Deletion of the gene encoding calcitonin and calcitonin gene-related peptide α does not affect the outcome of severe infection in mice

Procalcitonin (PCT) is expressed in nonthryoidal tissues of humans during severe infections. Serum PCT levels are measured to diagnose and guide therapy, and there is some evidence that PCT may also contribute to the pathogenesis of sepsis. We tested whether disruption of the gene encoding PCT in mice affected the course of sepsis. Mice with exons 2-5 of the gene encoding calcitonin/calcitonin gene-related polypeptide α (Calca) knocked out and congenic C57BL/6J control mice were challenged with aerosolized Streptococcus pneumoniae or Pseudomonas aeruginosa, or injected intraperitoneally with S. pneumoniae. There were no significant differences in the survival of knockout and control mice in the two pneumonia models, and no significant differences in weight loss, splenic bacterial counts, or blood leukocyte levels in the peritoneal sepsis model. To verify disruption of the Calca gene in knockout mice, the absence of calcitonin in the serum of knockout mice and its presence and inducibility in control mice were confirmed. To evaluate PCT expression in nonthyroidal tissues of control mice, transcripts were measured in multiple organs. PCT transcripts were not significantly expressed in liver or spleen of control mice challenged with aerosolized P. aeruginosa or intraperitoneal endotoxin, and were expressed in lung only at low levels, even though serum IL-6 rose 3,548-fold. We conclude that mice are not an ideal loss-of-function model to test the role of PCT in the pathogenesis of sepsis because of low nonendocrine PCT expression during infection and inflammation. Nonetheless, our studies demonstrate that nonendocrine PCT expression is not necessary for adverse outcomes from sepsis.

Procalcitonin as a biomarker of acute lower respiratory tract infections

BACKGROUND

Procalcitonin (PCT) has emerged as a promising 'acute phase' biomarker used for diagnosis of acute bacterial infections of the respiratory tract. The introduction of new sensitive PCT assays has facilitated implementation of a new clinical approach to reduce antibiotic use in acute lower respiratory tract infections (LRTIs), without compromising patient safety.

OBJECTIVE

Current state of knowledge on the clinical usefulness of serum PCT measurements for the evaluation of acute LRTIs is presented herein, together with basic information on available rapid diagnostic tests for PCT measurement.

METHODS

During the literature search the emphasis was on PCT use as a diagnostic, monitoring and prognostic tool for acute LRTIs. The acute LRTIs have been defined as acute bronchitis, acute exacerbations of chronic obstructive pulmonary disease or asthma, and pneumonia. Original studies involving patients with these conditions have been considered, and recent articles documenting interventional trials on PCT use for guidance of antimicrobial treatment in LRTIs have been reviewed in particular.

RESULTS/CONCLUSION

When measured with sensitive and rapid assays, PCT has proved to be a good biomarker for acute bacterial LRTIs, which enables an early diagnosis, facilitates therapeutic decisions, and can inform clinicians about the course of disease and prognosis. PCT can become a particularly suitable tool for implementation in an emergency and acute medical care setting.

Should heparin-binding protein levels be routinely monitored in patients with severe sepsis and septic shock?

Heparin-binding protein (HBP), also known as azurocidin, has multiple functions in the inflammatory process, especially during severe infections. Beside its antimicrobial properties, HBP may induce vascular leakage leading to extravascular efflux, which is an important pathophysiologic event in the development of septic shock. Not surprisingly, high HBP plasma levels are found in severe sepsis patients and in septic shock patients as well as in serious infections associated with endothelial damage. In the present issue of Critical Care, Linder and colleagues demonstrate new aspects of HBP daily monitoring in ICU patients. The authors observed that high HBP plasma levels are associated with an increased mortality rate in both septic and nonseptic critically ill patients, indicating that HBP may be a reliable prognostic biomarker. However, there are some limitations hindering rapid translation of these interesting findings into the daily routine. First, the group of nonseptic critically ill patients (n = 28) enrolled in the study was rather small as compared with the septic group (n = 151). Moreover, 50% of nonseptic patients developed infection while hospitalized in the ICU, and to classify them as truly nonseptic patients is problematic. Second, there is a lack of a routine diagnostic method for HBP analysis. Nevertheless, if the results of the present study are validated in large clinical trials in different ICU populations and cost-effectiveness data become available, the serial HBP measurements will have a promising future.

Immune regulation of procalcitonin: a biomarker and mediator of infection

Procalcitonin (PCT) has recently emerged as a powerful biomarker for an early and accurate diagnosis of bacterial infection. Here we summarize our current understanding of the expression pathways of PCT, its potential cellular sources including immune cells, and factors inducing its secretion. Also addressed is the significance of increased blood PCT concentration, which may allow this molecule not only to act as a clinical biomarker but also as an active participant in the development and progression of infectious processes. Experimental approaches to delineate a better understanding of PCT functions, molecular pathways that modulate its expression and therapeutic opportunities to curtail its biological actions are discussed, as well.

Intravenous immunoglobulin prevents release of proinflammatory cytokines in human monocytic cells stimulated with procalcitonin

OBJECTIVE

The aim of this study was to investigate whether the stimulation of monocytic cells with procalcitonin (PCT) results in the release of proinflammatory cytokines. The effects of intravenous immunoglobulin (IVIG) on the production of cytokines from the cells stimulated with PCT were also studied.

MATERIALS AND METHODS

Cultured monocytic cells [THP-1 cells treated with phorbol myristate acetate or peripheral blood mononuclear cells (PBMCs)] were stimulated with PCT. The protein levels of proinflammatory cytokines [tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and high mobility group box-1] in the culture supernatants were determined by ELISA kits. The concentration of PCT-specific IgG antibody in IVIG was measured using a specific ELISA.

RESULTS

PCT induced the release of cytokines from THP-1 cells in a time- and dose-dependent manner. IVIG inhibited the release of cytokines from the cells stimulated with PCT. It was confirmed that IVIG also inhibited TNF-α release in the same dose range for PBMCs stimulated with PCT. The presence of PCT-specific IgG antibody was detected in the tested IVIG, which might be one of the mechanisms.

CONCLUSIONS

PCT induced the release of proinflammatory cytokines from THP-1 cells and PBMCs. The function of PCT was prevented by the presence of IVIG.

Procalcitonin gene expression after LPS stimulation in the porcine animal model

Procalcitonin (PCT), recognised as a marker of sepsis, was investigated in a porcine model of endotoxic shock. The results showed that continuous IV infusion (1-4 h) of LPS (40 μg/kg) in pigs was able to induce a generalised increase of PCT expression in lung, heart, kidney and liver. The increase in PCT was significant only in kidney and was accompanied by an increase in IL-6 gene expression. In vitro results demonstrated that peripheral blood mononuclear cells (PBMCs), as well as endothelial cells, were potentially capable of contributing to in vivo extrathyroidal PCT production. These findings support previous data from pigs concerning the occurrence of widespread activation of PCT extrathyroidal gene expression during endotoxic shock in pigs. Nevertheless, the levels of PCT detected were very low, suggesting the need for additional studies to validate the pig as a reliable animal model for investigating the role of PCT in sepsis.

Immunoneutralization of the aminoprocalcitonin peptide of procalcitonin protects rats from lethal endotoxaemia: neuroendocrine and systemic studies

Severe sepsis and septic shock are an important cause of mortality and morbidity. These illnesses can be triggered by the bacterial endotoxin LPS (lipopolysaccharide) and pro-inflammatory cytokines, particularly TNF-α (tumour necrosis factor-α) and IL (interleukin)-1β. Severity and mortality of sepsis have also been associated with high concentrations of N-PCT (aminoprocalcitonin), a 57-amino-acid neuroendocrine peptide derived from ProCT (procalcitonin). Previous studies in a lethal model of porcine polymicrobial sepsis have revealed that immunoneutralization with IgG that is reactive to porcine N-PCT significantly improves short-term survival. To explore further the pathophysiological role of N-PCT in sepsis, we developed an antibody raised against a highly conserved amino acid sequence of human N-PCT [N-PCT-(44-57)]. This sequence differs by only one amino acid from rat N-PCT. First, we demonstrated the specificity of this antibody in a well-proven model of anorexia induced in rats by central administration of human N-PCT-(1-57). Next we explored further the therapeutic potential of anti-N-PCT-(44-57) in a rat model of lethal endotoxaemia and determined how this immunoneutralization affected LPS-induced lethality and cytokine production. We show that this specific antibody inhibited the LPS-induced early release of TNF-α and IL-1β and increased survival, even if treatment began after the cytokine response had occurred. In addition, anti-N-PCT-(44-57) may increase long-term survival in LPS-treated rats by up-regulating the late production of counter-regulatory anti-inflammatory mediators such as ACTH (adrenocorticotropic hormone) and IL-10. In conclusion, these results support N-PCT as a pro-inflammatory factor in both the early and the late stages of lethal endotoxaemia, and suggest anti-N-PCT as a candidate for septic shock therapy.

Immunoneutralization of procalcitonin or its component peptides: a promising treatment of sepsis

Sepsis and the severe systemic response syndrome are very common illnesses that are responsible for a great amount of morbidity and death. These closely related conditions are characterized by a remarkable increase in the prohormone ProCT (procalcitonin). ProCT is both a marker of sepsis and a harmful mediator of the disease. In the present issue of Clinical Science, in a study in rats with endotoxin shock, Tavares and Miñano used an antibody to a segment of N-ProCT (aminoprocalcitonin) that is part of the ProCT molecule, and confirmed that immunoneutralization of ProCT saves the animals from this severe illness. Furthermore, they extensively studied the epiphenomena associated with this immunoneutralization.

Procalcitonin for guidance of antibiotic therapy

Procalcitonin is a surrogate biomarker for estimating the likelihood of a bacterial infection. Procalcitonin-guided initiation and termination of antibiotic therapy is a novel approach utilized to reduce antibiotic overuse. This is essential to decrease the risk of side effects and emerging bacterial multiresistance. Interpretation of procalcitonin levels must always comprise the clinical setting and knowledge about assay characteristics. Only highly sensitive procalcitonin assays should be used in clinical practice and cut-off ranges must be adapted to the disease and setting. Highly sensitive procalcitonin measurements, embedded in diagnosis-specific clinical algorithms, have been shown to markedly reduce the overuse of antibiotic therapy without increasing risk to patients in 11 randomized controlled trials including over 3500 patients from different European countries. In primary care and emergency department patients with mild and mostly viral respiratory infections (acute bronchitis), the initial prescription of antibiotics was reduced by 30-80%. In hospitalized and more severely ill patients with community-acquired pneumonia and sepsis, the main effect was a reduction of the duration of antibiotic courses by 25-65%. This review aims to provide physicians with an overview of the strengths and limitations of procalcitonin guidance for antibiotic therapy when used in different clinical settings and in patients with different underlying infections.

Procalcitonin in sepsis and systemic inflammation: a harmful biomarker and a therapeutic target

The worldwide yearly mortality from sepsis is substantial, greater than that of cancer of the lung and breast combined. Moreover, its incidence is increasing, and its response to therapy has not appreciably improved. In this condition, the secretion of procalcitonin (ProCT), the prohormone of calcitonin, is augmented greatly, attaining levels up to thousands of fold of normal. This hypersecretion emanates from multiple tissues throughout the body that are not traditionally viewed as being endocrine. The serum values of ProCT correlate with the severity of sepsis; they recede with its improvement and worsen with exacerbation. Accordingly, as highlighted in this review, serum ProCT has become useful as a biomarker to assist in the diagnosis of sepsis, as well as related infectious or inflammatory conditions. It is also a useful monitor of the clinical course and prognosis, and sensitive and specific assays have been developed for its measurement. Moreover, it has been demonstrated that the administration of ProCT to septic animals greatly increases mortality, and several toxic effects of ProCT have been elucidated by in vitro experimental studies. Antibodies have been developed that neutralize the harmful effects of ProCT, and their use markedly decreases the symptomatology and mortality of animals that harbour a highly virulent sepsis analogous to that occurring in humans. This therapy is facilitated by the long duration of serum ProCT elevation, which allows for a broad window of therapeutic opportunity. An experimental groundwork has been established that suggests a potential applicability of such therapy in septic humans.

Procalcitonin as a marker of severe bacterial infection in children in the emergency department

Procalcitonin, the prohormone of calcitonin, is a relatively new and innovative marker of bacterial infection that has multiple potential applications in the pediatric emergency department. In healthy individuals, circulating levels of procalcitonin are generally very low (<0.05 ng/mL), but in the setting of severe bacterial infection and sepsis, levels can increase by hundreds to thousands of fold within 4 to 6 hours. Although the exact physiologic function of procalcitonin has not been determined, the consistent response and rapid rise of this protein in the setting of severe bacterial infection make procalcitonin a very useful biomarker for invasive bacterial disease. In Europe, serum procalcitonin measurements are frequently used in the diagnosis and the management of patients in a variety of clinical settings. To date, the use of procalcitonin has been limited in the United States, but this valuable biomarker has many potential applications in both the pediatric emergency department and the intensive care unit. The intent of this article is to review the history of procalcitonin, describe the kinetics of the molecule in response to bacterial infection, describe the laboratory methods available for measuring procalcitonin, examine the main causes of procalcitonin elevation, and evaluate the potential applications of procalcitonin measurements in pediatric patients.

Method for the Selective Measurement of Amino-Terminal Variants of Procalcitonin

Background: Procalcitonin (PCT) is an established marker for diagnosing and monitoring bacterial infections. Full-length PCT [116 amino acids that make up procalcitonin (PCT1–116)] can be truncated, leading to des-Ala-Pro-PCT (des-Alanin-Prolin-Procalcitonin; PCT3–116). Current immunoassays for PCT (“total PCT”) use antibodies directed against internal epitopes and are unable to distinguish amino-terminal PCT variants. Here we describe the development of monoclonal antibodies recognizing the amino-termini of PCT1–116 and PCT3–116 and their use in the selective measurement of these PCT species.

Methods: With newly developed monoclonal antibodies against the amino-termini of PCT1–116 and PCT3–116, and an antibody against the katacalcin moiety of PCT, we developed and characterized immunoluminometric assays for the 2 PCT peptides. We comparatively assessed the kinetics of PCT variants in a human endotoxemia model.

Results: Monoclonal antibodies against the amino-termini of PCT1–116 and PCT3–116 showed &lt;1% cross-reactivity with other PCT-related peptides. The sandwich assays for PCT1–116 and PCT3–116 had functional assay sensitivities of 5 and 1.2 pmol/L, respectively, and exhibited recoveries within 20% of expected values. Plasma PCT1–116 was stable for 6 h at 22 °C and 24 h at 4 °C, and PCT3–116 was stable for at least 24 h at both temperatures. During experimental endotoxemia in healthy people, both PCT1–116 and PCT3–116 increased early in parallel with total PCT, but further increases in PCT1–116 were significantly slower than for PCT3–116 (P = 0.0049) and total PCT (P = 0.0024).

Conclusions: The new assays selectively measure PCT1–116 and PCT3–116. Both PCT species increase early during endotoxemia but differ in their kinetics thereafter. The selective measurement of PCT species with different in vivo kinetics may be useful in improving PCT-guided therapies.

No association between CALCA polymorphisms and clinical outcome or serum procalcitonin levels in German polytrauma patients

PURPOSE

Procalcitonin (PCT) is accepted to be a relevant prognostic marker for the development of clinical complications in multiple trauma patients. Therefore, a prospective cohort study was conducted to investigate whether polymorphisms in the calcitonin (CALCA) gene are associated with PCT levels and posttraumatic complications.

METHODS

During a 14day observation period, blood samples were drawn once daily for systemic PCT concentrations in multiple trauma patients (Injury Severity Score >16). For analysis of allele frequencies, genotype distribution and PCT concentrations polytraumatized patients were separated, according to the development of SIRS, sepsis, septic shock, ARDS, MODS and mortality. Furthermore, association between CALCA polymorphisms and PCT plasma concentrations was assessed.

RESULTS

One hundred thirty seven patients with a mean ISS of 29.2+/-12.1 were included. When trauma patients were grouped according to different posttraumatic complications no association with CALCA SNPs was observed. Additionally, no association was found between CALCA polymorphisms and systemic PCT levels.

CONCLUSION

CALCA polymorphisms are unlikely to influence clinical outcome in polytraumatized patients. Effects of microbial and inflammatory mediators, as well as other risk factors (gender, age, etc.) seem to have a more significant influence on the transcriptional regulation of CALCA and on PCT plasma concentrations than CALCA polymorphisms.

Serum concentrations of procalcitonin after cardiac surgery

BACKGROUND AND AIM

Monitoring of complications in patients undergoing cardiac surgery may be difficult because cardiopulmonary bypass (CPB) can lead to a systemic inflammatory response syndrome because of exposure of blood to nonphysiological surfaces. The purpose of the study was to establish the baseline levels of procalcitonin (PCT) after cardiac surgery in our population in order to analyze a possible induction of the inflammatory response that might interfere with the diagnosis of infection by PCT.

METHODS

Serum samples from patients undergoing coronary artery bypass grafting or valve replacement were collected at the time of admission to intensive care unit, after surgery as well as in the first and second postoperative days. Patients were followed for the development of postoperative complications. PCT levels were measured by immunoluminometric assay.

RESULTS

The mean PCT values were significantly higher in the first postoperative day in all the groups except the control group. No increased PCT levels were found related neither to duration of CPB, nor to time of aortic clamping. Only patients who presented complications had significantly increased PCT values immediately after surgery (p = 0.004), in the first postoperative day (p < 0.0001), and in the second postoperative day (p < 0.0001) with respect to those who recovered uneventfully.

CONCLUSIONS

A slight and transient increase in PCT levels was observed in the first postoperative day after cardiac surgery. Significant elevation of PCT was only observed when complications were present.

Biomarkers: diagnosis and risk assessment in sepsis

Prompt diagnosis, intervention, and risk assessment are critical in caring for septic patient but remain difficult with currently available methods. Biomarkers may become useful adjuncts to clinicians and ultimately serve as targets for future therapeutic trials in sepsis. The most relevant markers are reviewed in this article, including interleukin-6, C-reactive protein, procalcitonin, triggering receptor expressed on myeloid cells-1, and biomarker panels.