Background: The colloidal gold immunochromatography assay (GICA) is a rapid diagnostic tool for novel coronavirus disease 2019 (COVID-19) infections. However, with significant numbers of false negatives, improvements to GICA are needed. Methods: Six recombinant HCoV-19 nucleocapsid and spike proteins were prepared and evaluated. The optimal proteins were employed to develop a sandwich-format GICA strip to detect total antibodies (IgM and IgG) against HCoV-19. GICA’s performance was assessed with comparison of viral RNA detection. Results: Recombinant HCoV-19 proteins were obtained, including three prokaryotically expressed rN, rN1, rN2 nucleocapsid proteins, and three eukaryotically expressed rS1, rS-RBD, rS-RBD-mFc spike proteins. The recombinant proteins with the highest ELISA titers (rS1 and rS-RBD-mFc) against coronavirus-specific IgM and IgG were chosen for GICA development. The GICA has a sensitivity and specificity of 86.89% (106/122) and 99.39% (656/660), respectively. Furthermore, 65.63% (21/32) of the clinically confirmed but RT-PCR negative samples were GICA positive. Conclusions: The eukaryotically-expressed spike proteins (rS1and rS-RBD-mFc) are more suitable than the prokaryotically expressed nucleocapsid proteins for HCoV-19 serological diagnosis. The GICA sandwich used to detect total antibodies is a powerful complement to the current standard RNA-based tests.

We have previously reported that high-alcohol-producing Klebsiella pneumoniae (HiAlc Kpn) in the gut can cause endo-alcoholic fatty liver disease. Here, we discover that 91.2% of Kpn isolates from pulmonary disease samples also produce excess ethanol, which may be associated with respiratory disease severity. To further explore the potential mechanism, a murine model is established with high-dose bacteria. Kpn stimulates granular neutrophils (G0), subsequently transforming them into phagocytic neutrophils (G1). HiAlc Kpn also causes dysfunction of pyrimidine metabolism, leading to neutrophil apoptosis. These changes inhibit phagocytosis of neutrophils and possibly suppress inflammasome-dependent innate immunity. In a persistent infective murine model, HiAlc Kpn induces lung fibrosis and production of reactive oxygen species (ROS), possibly affecting epithelial cell apoptosis and lung function. The results suggest that the subtype of neutrophil is a potential biomarker for the severity of lung injury caused by HiAlc Kpn.