key: cord-0934742-s6z3z35n authors: d'Alessandro, Miriana; Cameli, Paolo; Refini, Rosa Metella; Bergantini, Laura; Alonzi, Valerio; Lanzarone, Nicola; Bennett, David; Rana, Giuseppe Domenico; Montagnani, Francesca; Scolletta, Sabino; Franchi, Federico; Frediani, Bruno; Valente, Serafina; Mazzei, Maria Antonietta; Bonella, Francesco; Bargagli, Elena title: Serum KL‐6 concentrations as a novel biomarker of severe COVID‐19 date: 2020-06-09 journal: J Med Virol DOI: 10.1002/jmv.26087 sha: be25a5844f3d820a1bb0a3a8e7f20ee63651e884 doc_id: 934742 cord_uid: s6z3z35n Severe acute respiratory syndrome coronavirus 2–induced direct cytopathic effects against type I and II pneumocytes mediate lung damage. Krebs von den Lungen‐6 (KL‐6) is mainly produced by damaged or regenerating alveolar type II pneumocytes. This preliminary study analyzed serum concentrations of KL‐6 in patients with coronavirus disease (COVID‐19) to verify its potential as a prognostic biomarker of severity. Twenty‐two patients (median age [interquartile range] 63 [59‐68] years, 16 males) with COVID‐19 were enrolled prospectively. Patients were divided into mild‐moderate and severe groups, according to respiratory impairment and clinical management. KL‐6 serum concentrations and lymphocyte subset were obtained. Peripheral natural killer (NK) cells/µL were significantly higher in nonsevere patients than in the severe group (P = .0449) and the best cut‐off value was 119 cells/µL. KL‐6 serum concentrations were significantly higher in severe patients than the nonsevere group (P = .0118). Receiver operating characteristic analysis distinguished severe and nonsevere patients according to KL‐6 serum levels and the best cut‐off value was 406.5 U/mL. NK cell analysis and assay of KL‐6 in serum can help identify severe COVID‐19 patients. Increased KL‐6 serum concentrations were observed in patients with severe pulmonary involvement, revealing a prognostic value and supporting the potential usefulness of KL‐6 measurement to evaluate COVID‐19 patients' prognosis. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan (China) in December 2019 and was declared pandemic by the World Health Organization (WHO) in March 2020. It has been hypothesized that CD4-and CD8-positive cells play a crucial role in defence against coronavirus, together with activated B cells producing specific antibodies and proinflammatory cytokines. Elevated serum concentrations of proinflammatory cytokines and oxidative stress mediators participate in lung injury, facilitating acute respiratory distress syndrome (ARDS) in severe patients. Host susceptibility and virus-induced direct cytopathic effects against type I and II pneumocytes mediate lung damage. Krebs von den Lungen-6 (KL-6) is a high molecular weight glycoprotein, elevated in serum of patients with interstitial lung diseases (ILDs), such as idiopathic pulmonary fibrosis and hypersensitivity pneumonitis. It is mainly produced by damaged or regenerating alveolar type II pneumocytes. 1 This mucin protein is recognized as a prognostic bioindicator of ILDs, predicting response to antifibrotic therapies. [2] [3] [4] It has also been proposed as a prognostic marker of ARDS: high KL-6 concentrations have been demonstrated in ventilated patients and showed a correlation with risk of mortality. 5 KL-6 serum levels in ARDS may reflect the alveolar epithelial cell damage induced by mechanical ventilatory support. 5 High peripheral levels of this protein have also been reported in Legionella, Pneumocystis jivorecii infections, 6,7 and measles-associated pneumonia, 8 as well as in viral pneumonia. 9 This preliminary study analyzed serum concentrations of KL-6 for the first time in a population of hospitalized coronavirus disease (COVID-19) patients to verify its potential as a prognostic biomarker of severity. years, six males) were also enrolled. They had no history of concomitant pathologies and were not on any medication. They had normal lung function test parameters and normal chest X-ray. All patients gave their written informed consent to the study. The study was approved by our local ethics committee (BIOBANCA-MIU-2010). Serum samples were obtained from all patients at hospital admission before any biological treatment or infusion of high-dose intravenous steroids or invasive ventilation. Serum concentrations of KL-6 (sKL-6) were measured by KL-6 reagent assay (Fujirebio Europe, UK), as previously reported. 2, 4, 10 The principle of the assay is agglutination of sialylated carbohydrate antigen in samples with KL-6 monoclonal antibody by antigen-antibody reaction. The change in absorbance was measured to determine KL-6 concentrations, which were expressed in U/mL. The data did not show a normal distribution. One-way analysis of variance nonparametric test (Kruskal-Wallis test) and Dunn test were used for multiple comparisons. The Mann-Whitney test was used to compare pairs of variables. The χ 2 test was used for categorical variables as appropriate. Immunological data were also compared between the severe and nonsevere groups, assessing areas under the receiver operating characteristic (ROC) curves (AUC). 55-100; P = .0425; Figure 1A ) and the best cut-off value was 119 cells/µL (71% sensitivity and 92% specificity). In this study, KL-6 was analyzed for the first time in a population of patients with COVID-19. Serum concentrations of KL-6 were only elevated in severe patients admitted to the ICU and requiring intubation and mechanical ventilation for diffuse interstitial pneumonia, and not in mild-moderate patients with less severe respiratory impairment. Patients with mild-moderate COVID interstitial pneumonia showed serum concentrations of KL-6 similar to those of healthy controls. Although these results are preliminary (this was a monocentric study with a limited number of patients), they are of interest because KL-6 emerged as a potential prognostic biomarker readily detected in serum of COVID-19 patients and helpful for phenotyping patients according to disease severity. This mucin protein has been widely studied in idiopathic pulmonary fibrosis and patients with ARDS but limited data have so far been available on its prognostic potential in infective pneumonia. 1, 5, 9 No data have hitherto been available on its pattern in coronavirus-induced interstitial pneumonia. Our interest was aroused by the observation that Severe cases (n = 12) Nonsevere cases (n = 10) P-value This study was generated within the European Reference Network for Rare Respiratory Diseases (ERN-LUNG). The study was performed at Siena University. Serum KL-6 levels reflect the severity of interstitial lung disease associated with connective tissue disease Serum KL-6 levels in pulmonary Langerhans' cell histiocytosis Receiver operating characteristic (ROC) analysis of natural killer cells/µL between severe and nonsevere coronavirus disease (COVID-19) patients. B, Krebs von den Lungen-6 (KL-6) concentrations in COVID-19 patients and healthy controls. (P < .05). C, ROC analysis of serum KL-6 concentrations between severe Serial KL-6 analysis in patients with idiopathic pulmonary fibrosis treated with nintedanib BAL biomarkers' panel for differential diagnosis of interstitial lung diseases KL-6 levels are elevated in plasma from patients with acute respiratory distress syndrome Clinical utility of serum beta-D-glucan and KL-6 levels in Pneumocystis jirovecii pneumonia Serial change in serum biomarkers during treatment of non-HIV Pneumocystis pneumonia Clinical significance of the serum surfactant protein D and KL-6 levels in patients with measles complicated by interstitial pneumonia Serum KL-6 levels as a biomarker of lung injury in respiratory syncytial virus bronchiolitis Bronchoalveolar lavage and serum KL-6 concentrations in chronic hypersensitivity pneumonitis: correlations with radiological and immunological features Peripheral lymphocyte subset monitoring in COVID19 patients: a prospective Italian real-life case series The authors declare that there are no conflict of interests.