Labeled TEMPO-Oxidized Mannan Differentiates Binding Profiles within the Collectin Families.

Establishing the rapid and accurate diagnosis of sepsis is a key component to the improvement of clinical outcomes. The ability of analytical platforms to rapidly detect pathogen-associated molecular patterns (PAMP) in blood could provide a powerful host-independent biomarker of sepsis. A novel concept was investigated based on the idea that a pre-bound and fluorescent ligand could be released from lectins in contact with high-affinity ligands (such as PAMPs). To create fluorescent ligands with precise avidity, the kinetically followed TEMPO oxidation of yeast mannan and carbodiimide coupling were used. The chemical modifications led to decreases in avidity between mannan and human collectins, such as the mannan-binding lectin (MBL) and human surfactant protein D (SP-D), but not in porcine SP-D. Despite this effect, these fluorescent derivatives were captured by human lectins using highly concentrated solutions. The resulting fluorescent beads were exposed to different solutions, and the results showed that displacements occur in contact with higher affinity ligands, proving that two-stage competition processes can occur in collectin carbohydrate recognition mechanisms. Moreover, the fluorescence loss depends on the discrepancy between the respective avidities of the recognized ligand and the fluorescent mannan. Chemically modulated fluorescent ligands associated with a diversity of collectins may lead to the creation of diagnostic tools suitable for multiplex array assays and the identification of high-avidity ligands.

Surfactant protein D (SP-D) as a biomarker of SARS-CoV-2 infection.

BACKGROUND: Surfactant protein-D (SP-D) is a lung-resident protein that has emerged as a potential biomarker for COVID-19. Previous investigations on acute respiratory distress syndrome patients demonstrated a significant increment of SP-D serum levels in pathological conditions. Since SP-D is not physiologically permeable to alveoli-capillary membrane and poorly expressed by other tissues, this enhancement is likely due to an impairment of the pulmonary barrier caused by prolonged inflammation. METHODS: A retrospective study on a relatively large cohort of patients of Hospital Pio XI of Desio was conducted to assess differences of the hematic SP-D concentrations among COVID-19 patients and healthy donors and if SP-D levels resulted a risk factor for disease severity and mortality. RESULTS: The first analysis, using an ANOVA-model, showed a significant difference in the mean of log SP-D levels between COVID-19 patients and healthy donors. Significant variations were also found between dead vs survived patients. Results confirm that SP-D concentrations were significantly higher for both hospitalized COVID-19 and dead patients, with threshold values of 150 and 250 ng/mL, respectively. Further analysis conducted with Logistic Mixed models, highlighted that higher SP-D levels at admission and increasing differences among follow-up and admission values resulted the strongest significant risk factors of mortality (model predictive accuracy, AUC = 0.844). CONCLUSIONS: The results indicate that SP-D can be a predictive marker of COVID-19 disease and its outcome. Considering its prognostic value in terms of mortality, the early detection of SP-D levels and its follow-up in hospitalized patients should be considered to direct the therapeutic intervention.

Coronavirus disease 2019 (COVID-19) in patients before, during, or after lung irradiation, and serum SP-A and SP-D levels.

BACKGROUND: The correlation between COVID-19 and RT has not been determined to date and remains a clinical question. The aim of this study was to evaluate coronavirus disease 2019 (COVID-19) pneumonia before, during, and after radiation therapy (RT) regarding the radiation doses, radiation pneumonitis, and surfactant protein levels. METHODS: We evaluated patients diagnosed with COVID-19 before, during, or after RT for the lung between August 2020 and April 2022. In patients with breast cancer, the RT dose to the ipsilateral lung was determined. In all other patients, bilateral lung RT doses were determined. Patients diagnosed with COVID-19 after RT were evaluated to determine whether radiation pneumonitis had worsened compared with before RT. The serum levels of the surfactant proteins SP-A and SP-D were measured before, during, and after RT. RESULTS: The patients included in the study comprised three men (27.3%) and eight women (72.7%). The primary cancer sites were the breast (n = 7; 63.7%), lung (n = 2; 18.1%), esophagus (n = 1; 9.1%), and tongue (9.1%). COVID-19 was diagnosed before RT in four patients, during RT in two patients, and after RT in five patients. Six (54.5%) patients developed COVID-19 pneumonia. Radiation pneumonitis grade ≥2 was not identified in any patient, and radiation pneumonitis did not worsen after RT in any patient. No rapid increases or decreases in SP-A and SP-D levels occurred after the diagnosis of COVID-19 in all patients regardless of RT timing. CONCLUSIONS: COVID-19 did not appear to result in lung toxicity and surfactant protein levels did not change dramatically.

Correlation of Surfactant Protein-D (SP-D) Serum Levels with ARDS Severity and Mortality in Covid-19 Patients in Indonesia.

OBJECTIVE: The purpose of this research was to investigate the correlation between serum levels of surfactant protein-D (SPD) with acute respiratory distress syndrome (ARDS) severity and mortality in COVID-19. MATERIALS AND METHOD: This was a prospective cohort research study that included 76 patients in the period from July to October 2020. SP-D serum levels were taken upon admission to the hospital, the diagnosis of ARDS and its grade were confirmed according to the WHO criteria, and then patients were observed for 28-day mortality. RESULTS: The mean SP-D serum levels from 76 patients were 39.33 ng/ml (SD±31.884 ng/ml). The statistical analysis showed that there was a significant correlation between SP-D serum levels and the severity of ARDS upon admission to the hospital (P=0.04, Spearman's rank correlation coefficient (rs)=0.26), but the correlation between serum levels of SP-D and mortality was not statistically significant (P=0.89; rs=-0.016). CONCLUSION: SP-D serum levels had a significant but weak correlation with ARDS severity, but were not significant for mortality.

Serum stratifin and presepsin as candidate biomarkers for early detection of COVID-19 disease progression.

The prognosis of patients with severe cases of COVID-19 is poor; thus, biomarkers for earlier prediction of COVID-19 progression are vital. We measured levels of five lung injury-related biomarkers, SP-D, KL-6, presepsin, kallistatin and stratifin, in serum samples collected serially during hospitalization from 31 patients with mild/moderate or severe/critical COVID-19 pneumonia, and their predictive performances were compared. Like the previously reported presepsin, a new biomarker candidate, stratifin, was significantly elevated with the onset of severe or critical symptoms in COVID-19 patients and decreased with symptom improvement. Notably, changes in stratifin and presepsin levels were distinctly earlier than those in SP-D, KL-6 and even SpO2/FiO2 values. Furthermore, serum levels of these biomarkers were significantly higher at the pre-severe stage (before the start of oxygen support) of patients who eventually advanced to severe/critical stages than in the patients who remained at the mild/moderate stage. These results were confirmed in an independent cohort, including 71 mild/moderate and 14 severe/critical patients, for whom the performance of stratifin and presepsin in discriminating between mild/moderate and pre-severe conditions of COVID-19 patients was superior to that of the SpO2/FiO2 ratio. Therefore, we concluded that stratifin and presepsin could be used as prognostic biomarkers for severe COVID-19 progression.

Serum surfactant protein D in COVID-19 is elevated and correlated with disease severity.

BACKGROUND: The serum surfactant protein D (SP-D) level is suggested to be a useful biomarker for acute lung injuries and acute respiratory distress syndrome. Whether the serum SP-D level could identify the severity of coronavirus disease 2019 (COVID-19) in the early stage has not been elucidated. METHODS: We performed an observational study on 39 laboratory-confirmed COVID-19 patients from The Fourth People's Hospital of Yiyang, Hunan, China. Receiver operating characteristic (ROC) curve analysis, correlation analysis, and multivariate logistic regression model analysis were performed. RESULTS: In the acute phase, the serum levels of SP-D were elevated significantly in severe COVID-19 patients than in mild cases (mean value ± standard deviation (SD), 449.7 ± 125.8 vs 245.9 ± 90.0 ng/mL, P<0.001), while the serum levels of SP-D in the recovery period were decreased dramatically than that in the acute phase (mean value ± SD, 129.5 ± 51.7 vs 292.9 ± 130.7 ng/ml, P<0.001), and so were for the stratified patients. The chest CT imaging scores were considerably higher in the severe group compared with those in the mild group (median value, 10.0 vs 9.0, P = 0.011), while markedly lower in the recovery period than those in the acute phase (median value, 2.0 vs 9.0, P<0.001), and so were for the stratified patients. ROC curve analysis revealed that areas under the curve of lymphocyte counts (LYM), C-reaction protein (CRP), erythrocyte sedimentation rate (ESR), interleukin-6 (IL-6), and SP-D for severe COVID-19 were 0.719, 0.833, 0.817, 0.837, and 0.922, respectively. Correlation analysis showed that the SP-D levels were negatively correlated with LYM (r = - 0.320, P = 0.047), while positively correlated with CRP (r = 0.658, P<0.001), IL-6 (r = 0.471, P = 0.002), the duration of nucleic acid of throat swab turning negative (r = 0.668, P<0.001), chest CT imaging score on admission (r = 0.695, P<0.001) and length of stay (r = 0.420, P = 0.008). Multivariate logistic regression model analysis showed that age (P = 0.041, OR = 1.093) and SP-D (P = 0.008, OR = 1.018) were risk factors for severe COVID-19. CONCLUSIONS: Elevated serum SP-D level was a potential biomarker for the severity of COVID-19; this may be useful in identifying patients whose condition worsens at an early stage.

Expression of Surfactant Protein D Distinguishes Severe Pandemic Influenza A(H1N1) from Coronavirus Disease 2019.

The differentiation between influenza and coronavirus disease 2019 (COVID-19) could constitute a diagnostic challenge during the ongoing winter owing to their clinical similitude. Thus, novel biomarkers are required to enable making this distinction. Here, we evaluated whether the surfactant protein D (SP-D), a collectin produced at the alveolar epithelium with known immune properties, was useful to differentiate pandemic influenza A(H1N1) from COVID-19 in critically ill patients. Our results revealed high serum SP-D levels in patients with severe pandemic influenza but not those with COVID-19. This finding was validated in a separate cohort of mechanically ventilated patients with COVID-19 who also showed low plasma SP-D levels. However, plasma SP-D levels did not distinguish seasonal influenza from COVID-19 in mild-to-moderate disease. Finally, we found that high serum SP-D levels were associated with death and renal failure among severe pandemic influenza cases. Thus, our studies have identified SP-D as a unique biomarker expressed during severe pandemic influenza but not COVID-19.

Full-Length Recombinant hSP-D Binds and Inhibits SARS-CoV-2.

SARS-CoV-2 infection of host cells is driven by binding of the SARS-CoV-2 spike-(S)-protein to lung type II pneumocytes, followed by virus replication. Surfactant protein SP-D, member of the front-line immune defense of the lungs, binds glycosylated structures on invading pathogens such as viruses to induce their clearance from the lungs. The objective of this study is to measure the pulmonary SP-D levels in COVID-19 patients and demonstrate the activity of SP-D against SARS-CoV-2, opening the possibility of using SP-D as potential therapy for COVID-19 patients. Pulmonary SP-D concentrations were measured in bronchoalveolar lavage samples from patients with corona virus disease 2019 (COVID-19) by anti-SP-D ELISA. Binding assays were performed by ELISAs. Protein bridge and aggregation assays were performed by gel electrophoresis followed by silver staining and band densitometry. Viral replication was evaluated in vitro using epithelial Caco-2 cells. Results indicate that COVID-19 patients (n = 12) show decreased pulmonary levels of SP-D (median = 68.9 ng/mL) when compared to levels reported for healthy controls in literature. Binding assays demonstrate that SP-D binds the SARS-CoV-2 glycosylated spike-(S)-protein of different emerging clinical variants. Binding induces the formation of protein bridges, the critical step of viral aggregation to facilitate its clearance. SP-D inhibits SARS-CoV-2 replication in Caco-2 cells (EC90 = 3.7 µg/mL). Therefore, SP-D recognizes and binds to the spike-(S)-protein of SARS-CoV-2 in vitro, initiates the aggregation, and inhibits viral replication in cells. Combined with the low levels of SP-D observed in COVID-19 patients, these results suggest that SP-D is important in the immune response to SARS-CoV-2 and that rhSP-D supplementation has the potential to be a novel class of anti-viral that will target SARS-CoV-2 infection.

The role of angiopoietin-2 and surfactant protein-D levels in SARS-CoV-2-related lung injury: A prospective, observational, cohort study.

INTRODUCTION: Coronavirus disease-2019 (COVID-19) is a respiratory disease whose clinical manifestation ranges from asymptomatic to severe respiratory failure. The purpose of this study was to investigate the place of serum surfactant-D (SP-D) and angiopoetin-2 (Ang-2) levels in predicting severity of disease in patients diagnosed with COVID-19. METHODS: Sixty-four patients diagnosed with COVID-19 between September 2020 and February 2021, 50 patients diagnosed with community-acquired pneumonia and a 50-member healthy control group were included in the study. Plasma samples and clinical data were collected within 72 h after admission, during hospital stay. Serum SP-D and Ang-2 concentrations were measured using the enzyme-linked immunosorbent assay. RESULTS: SP-D and Ang-2 levels were significantly higher in the mild-moderate pneumonia and severe/critical patient groups compared to the asymptomatic and noncomplicated COVID-19 patients (p < 0.001 for all groups). Serum SP-D and Ang-2 levels of severe-critical COVID-19 patients were significantly higher than CAP patients (p < 0.001). Powerful correlation was present between clinical severity of COVID-19 and SP-D and Ang-2 levels (r = 0.885 p < 0.001 and r = 0.913 p < 0.001, respectively). Cut-off values of 37.7 ng/ml (AUC = 0.763, p < 0.001, 95% confidence interval [CI] = 0.667-0.860) for SP-D and 4208.3 pg/ml (AUC = 0.659, p = 0.004, 95% CI = 0.554-0.763) for Ang-2 were identified as predictors of COVID-19 disease at receiver operating characteristic curve analysis. CONCLUSION: SP-D and Ang-2 are predictive factors in differentiating COVID-19 patients and determining severity of disease. These data may be important for the initiation of treatment in the early stage of the disease in patients with COVID-19.

Human Surfactant Protein D Binds Spike Protein and Acts as an Entry Inhibitor of SARS-CoV-2 Pseudotyped Viral Particles.

Human SP-D is a potent innate immune molecule whose presence at pulmonary mucosal surfaces allows its role in immune surveillance against pathogens. Higher levels of serum SP-D have been reported in the patients with severe acute respiratory syndrome coronavirus (SARS-CoV). Studies have suggested the ability of human SP-D to recognise spike glycoprotein of SARS-CoV; its interaction with HCoV-229E strain leads to viral inhibition in human bronchial epithelial (16HBE) cells. Previous studies have reported that a recombinant fragment of human SP-D (rfhSP-D) composed of 8 Gly-X-Y repeats, neck and CRD region, can act against a range of viral pathogens including influenza A Virus and Respiratory Syncytial Virus in vitro, in vivo and ex vivo. In this context, this study was aimed at examining the likely protective role of rfhSP-D against SARS-CoV-2 infection. rfhSP-D showed a dose-responsive binding to S1 spike protein of SARS-CoV-2 and its receptor binding domain. Importantly, rfhSP-D inhibited interaction of S1 protein with the HEK293T cells overexpressing human angiotensin converting enzyme 2 (hACE2). The protective role of rfhSP-D against SARS-CoV-2 infection as an entry inhibitor was further validated by the use of pseudotyped lentiviral particles expressing SARS-CoV-2 S1 protein; ~0.5 RLU fold reduction in viral entry was seen following treatment with rfhSP-D (10 µg/ml). These results highlight the therapeutic potential of rfhSP-D in SARS-CoV-2 infection and merit pre-clinical studies in animal models.

Downregulation of type III interferons in patients with severe COVID-19.

Coronavirus disease 2019 (COVID-19) is globally rampant, and to curb the growing burden of this disease, in-depth knowledge about its pathophysiology is needed. This was an observational study conducted at a single center to investigate serum cytokine and chemokine levels of COVID-19 patients, based on disease severity. We included 72 consecutive COVID-19 patients admitted to our hospital from March 21 to August 31, 2020. Patients were divided into Mild-Moderate I (mild) and Moderate II-Severe (severe) groups based on the COVID-19 severity classification developed by the Ministry of Health, Labor and Welfare (MHLW) of Japan. We compared the patient characteristics as well as the serum cytokine and chemokine levels on the day of admission between the two groups. Our findings indicated that the severe group had significantly higher levels of serum fibrinogen, d-dimer, lactate dehydrogenase, C-reactive protein, ferritin, Krebs von den Lungen-6, surfactant protein (SP)-D, and SP-A than the mild group. Strikingly, the levels of interleukin (IL)-28A/interferon (IFN)-λ2 were significantly lower in the severe group than in the mild group. We believe that reduced levels of type III interferons (IFN-λs) and alterations in the levels of other cytokines and chemokines may impact the severity of the disease.

A Recombinant Fragment of Human Surfactant Protein D Binds Spike Protein and Inhibits Infectivity and Replication of SARS-CoV-2 in Clinical Samples.

Coronavirus disease (COVID-19) is an acute infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human SP-D (surfactant protein D) is known to interact with the spike protein of SARS-CoV, but its immune surveillance against SARS-CoV-2 is not known. The current study aimed to examine the potential of a recombinant fragment of human SP-D (rfhSP-D) as an inhibitor of replication and infection of SARS-CoV-2. The interaction of rfhSP-D with the spike protein of SARS-CoV-2 and human ACE-2 (angiotensin-converting enzyme 2) receptor was predicted via docking analysis. The inhibition of interaction between the spike protein and ACE-2 by rfhSP-D was confirmed using direct and indirect ELISA. The effect of rfhSP-D on replication and infectivity of SARS-CoV-2 from clinical samples was assessed by measuring the expression of RdRp gene of the virus using quantitative PCR. In silico interaction studies indicated that three amino acid residues in the receptor-binding domain of spike protein of SARS-CoV-2 were commonly involved in interacting with rfhSP-D and ACE-2. Studies using clinical samples of SARS-CoV-2-positive cases (asymptomatic, n = 7; symptomatic, n = 8) and negative control samples (n = 15) demonstrated that treatment with 1.67 µM rfhSP-D inhibited viral replication by ∼5.5-fold and was more efficient than remdesivir (100 µM) in Vero cells. An approximately two-fold reduction in viral infectivity was also observed after treatment with 1.67 µM rfhSP-D. These results conclusively demonstrate that the rfhSP-D mediated calcium independent interaction between the receptor-binding domain of the S1 subunit of the SARS-CoV-2 spike protein and human ACE-2, its host cell receptor, and significantly reduced SARS-CoV-2 infection and replication in vitro.

Histone H4 potentiates neutrophil inflammatory responses to influenza A virus: Down-modulation by H4 binding to C-reactive protein and Surfactant protein D.

Neutrophils participate in the early phase of the innate response to uncomplicated influenza A virus (IAV) infection but also are a major component in later stages of severe IAV or COVID 19 infection where neutrophil extracellular traps (NETs) and associated cell free histones are highly pro-inflammatory. It is likely that IAV interacts with histones during infection. We show that histone H4 binds to IAV and aggregates viral particles. In addition, histone H4 markedly potentiates IAV induced neutrophil respiratory burst responses. Prior studies have shown reactive oxidants to be detrimental during severe IAV infection. C reactive protein (CRP) and surfactant protein D (SP-D) rise during IAV infection. We now show that both of these innate immune proteins bind to histone H4 and significantly down regulate respiratory burst and other responses to histone H4. Isolated constructs composed only of the neck and carbohydrate recognition domain of SP-D also bind to histone H4 and partially limit neutrophil responses to it. These studies indicate that complexes formed of histones and IAV are a potent neutrophil activating stimulus. This finding could account for excess inflammation during IAV or other severe viral infections. The ability of CRP and SP-D to bind to histone H4 may be part of a protective response against excessive inflammation in vivo.

Are Serum Interleukin 6 and Surfactant Protein D Levels Associated with the Clinical Course of COVID-19?

PURPOSE: SARS-CoV-2 (COVID-19) has infected more than 7 million people worldwide in the short time since it emerged in Wuhan, China in December 2019. The aim of this study was to investigate the relationship between serum interleukin 6 (IL-6) and surfactant protein D (SP-D) levels and the clinical course and prognosis of COVID-19. MATERIALS AND METHODS: The study included a total of 108 individuals: 88 patients who were diagnosed with COVID-19 by real-time PCR of nasopharyngeal swab samples and admitted to the Atatürk University Pulmonary Diseases and the Erzurum City Hospital Infectious Diseases department between March 24 and April 15, and 20 asymptomatic healthcare workers who had negative real-time PCR results during routine COVID-19 screening in our hospital. RESULTS: Patients who developed macrophage activation syndrome had significantly higher IL-6 and SP-D levels at the time of admission and on day 5 of treatment compared to the other patients (IL-6: p = 0.001 for both; SP-D: p = 0.02, p = 0.04). Patients who developed acute respiratory distress syndrome had significantly higher IL-6 and SP-D levels at both time points compared to those who did not (p = 0.001 for all). Both parameters at the time of admission were also significantly higher among nonsurvivors compared to survivors (IL-6: p = 0.001, SP-D: p = 0.03). CONCLUSION: In addition to IL-6, which has an important role in predicting course and planning treatment in COVID-19, SP-D may be a novel pneumoprotein that can be used in the clinical course, follow-up, and possibly in future treatments.

S1P lyase inhibition protects against sepsis by promoting disease tolerance via the S1P/S1PR3 axis.

BACKGROUND: One-third of all deaths in hospitals are caused by sepsis. Despite its demonstrated prevalence and high case fatality rate, antibiotics remain the only target-oriented treatment option currently available. Starting from results showing that low-dose anthracyclines protect against sepsis in mice, we sought to find new causative treatment options to improve sepsis outcomes. METHODS: Sepsis was induced in mice, and different treatment options were evaluated regarding cytokine and biomarker expression, lung epithelial cell permeability, autophagy induction, and survival benefit. Results were validated in cell culture experiments and correlated with patient samples. FINDINGS: Effective low-dose epirubicin treatment resulted in substantial downregulation of the sphingosine 1-phosphate (S1P) degrading enzyme S1P lyase (SPL). Consequent accumulation and secretion of S1P in lung parenchyma cells stimulated the S1P-receptor type 3 (S1PR3) and mitogen-activated protein kinases p38 and ERK, reducing tissue damage via increased disease tolerance. The protective effects of SPL inhibition were absent in S1PR3 deficient mice. Sepsis patients showed increased expression of SPL, stable expression of S1PR3, and increased levels of mucin-1 and surfactant protein D as indicators of lung damage. INTERPRETATION: Our work highlights a tissue-protective effect of SPL inhibition in sepsis due to activation of the S1P/S1PR3 axis and implies that SPL inhibitors and S1PR3 agonists might be potential therapeutics to protect against sepsis by increasing disease tolerance against infections. FUNDING: This study was supported by the Center for Sepsis Control and Care (CSCC), the German Research Foundation (DFG), RTG 1715 (to M. H. G. and I. R.) and the National Institutes of Health, Grant R01GM043880 (to S. S.).