Numbers of patients with coronavirus disease 2019 (COVID-19) have increased rapidly worldwide. Plasma levels of full-length galectin-9 (FL-Gal9) and osteopontin (FL-OPN) as well as their truncated forms (Tr-Gal9, Ud-OPN, respectively), are representative inflammatory biomarkers. Here, we measured FL-Gal9, FL-OPN, Tr-Gal9, and Ud-OPN in 94 plasma samples obtained from 23 COVID-19-infected patients with mild clinical symptoms (CV), 25 COVID-19 patients associated with pneumonia (CP), and 14 patients with bacterial infection (ID). The four proteins were significantly elevated in the CP group when compared with healthy individuals. ROC analysis between the CV and CP groups showed that C-reactive protein had the highest ability to differentiate, followed by Tr-Gal9 and ferritin. Spearman’s correlation analysis showed that Tr-Gal9 and Ud-OPN but not FL-Gal9 and FL-OPN, had a significant association with laboratory markers for lung function, inflammation, coagulopathy, and kidney function in CP patients. CP patients treated with tocilizumab had reduced levels of FL-Gal9, Tr-Gal9, and Ud-OPN. It was suggested that OPN is cleaved by interleukin-6-dependent proteases. These findings suggest that the cleaved forms of OPN and galectin-9 can be used to monitor the severity of pathological inflammation and the therapeutic effects of tocilizumab in CP patients.

Acquired immunodeficiency syndrome (AIDS) complicated with tuberculosis (TB) is a global public issue. Due to the paucity of bacteria in AIDS/TB, blood-based biomarkers that reflect disease severity are desired. Plasma levels of matricellular proteins, such as osteopontin (OPN) and galectin-9 (Gal-9), are known to be elevated in AIDS and TB. Therefore, full-length (FL)-Gal9 and FL-OPN, and their truncated forms (Tr-Gal9, Ud-OPN), and 38 cytokines/chemokines were measured in the plasma of 24 AIDS (other than TB), 49 TB, and 33 AIDS/TB patients. Receiver-operating characteristic analysis was used to screen molecules that could distinguish either between disease and normal group, among each disease group, or between deceased patients and survivors. Selected molecules were further analyzed for significant differences. Tr-Gal9 had the highest ability to differentiate TB from AIDS or AIDS/TB, while Ud-OPN distinguished multidrug resistance (MDR)-TB from non-MDR TB, and extra-pulmonary TB from pulmonary TB. Molecules significantly elevated in deceased patients included; FL-Gal9, Tr-Gal9, interleukin (IL)-1 receptor antagonist, IL-17A and transforming growth factor-α in AIDS; IL-6, granulocyte colony-stimulating factor and monocyte chemotactic protein-1 in TB; and macrophage inflammatory protein-1β in AIDS/TB. From the sensitivity, specificity, and significant elevation, Tr-Gal9 is the best biomarker of inflammation and severity in AIDS and AIDS/TB.

Galectin-9 (Gal-9) is known to contribute to antiviral responses in coronavirus disease 2019 (COVID-19). Increased circulating Gal-9 in COVID-19 is associated with COVID-19 severity. In a while, the linker-peptide of Gal-9 is susceptible to proteolysis that can cause the change or loss of Gal-9 activity. Here, we measured plasma levels of N-cleaved-Gal9, which is Gal9 carbohydrate-recognition domain at the N-terminus (NCRD) with attached truncated linker peptide that differs in length depending on the type of proteases, in COVID-19. We also investigated the time course of plasma N-cleaved-Gal9 levels in severe COVID-19 treated with tocilizumab (TCZ). As a result, we observed an increase in plasma N-cleaved-Gal9 levels in COVID-19 and its higher levels in COVID-19 with pneumonia compared to the mild cases (healthy: 326.1 pg/mL, mild: 698.0 pg/mL, and with pneumonia: 1570 pg/mL). N-cleaved-Gal9 levels were associated with lymphocyte counts, C-reactive protein (CRP), soluble interleukin-2 receptor (sIL-2R), D-dimer, and ferritin levels, and ratio of percutaneous oxygen saturation to fraction of inspiratory oxygen (S/F ratio) in COVID-19 with pneumonia and discriminated different severity groups with high accuracy (area under the curve (AUC): 0.9076). Both N-cleaved-Gal9 and sIL-2R levels were associated with plasma matrix metalloprotease (MMP)-9 levels in COVID-19 with pneumonia. Furthermore, a decrease in N-cleaved-Gal9 levels was associated with a decrease of sIL-2R levels during TCZ treatment. N-cleaved-Gal9 levels showed a moderate accuracy (AUC: 0.8438) for discriminating the period before TCZ from the recovery phase. These data illustrate that plasma N-cleaved-Gal9 is a potential surrogate marker for assessing COVID-19 severity and the therapeutic effects of TCZ.