Analysis of Leukocyte Subpopulations by Flow Cytometry during Hospitalization Depending on the Severity of COVID-19 Course

The Association of Blood Eosinophils and Neutrophils Expressing Eosinophilic Surface Markers with the Severity and Outcome of COVID-19

(1) Background: The implication of type 2 (T2) inflammatory response in COVID-19 remains controversial. This study aimed to evaluate the association of eosinophils, neutrophils expressing eosinophilic surface markers and T2 cytokines with the severity and outcome of COVID-19. (2) Methods: Patients who were admitted to hospital due to COVID-19 from 18 December 2022 to 31 January 2023 were enrolled. Peripheral blood WBC and differentials, T2 cellular markers (subsets of eosinophils and neutrophils expressing eosinophilic surface markers) and cytokines at admission were measured and compared between subjects with different disease severities and outcomes. (3) Results: Ten mild-to-moderate and 22 severe-to-very severe cases were enrolled for analysis. Of these patients, seven died of severe-to-very severe disease. The severe-to-very severe patients showed a higher number of neutrophils, but lower numbers of eosinophils, lymphocytes cells and neutrophils expressing eosinophilic surface markers. Similarly, deceased cases were also characterized by increased neutrophils, but decreased eosinophils and neutrophils expressing eosinophilic surface markers. The levels of T2 cytokines failed to demonstrate a significant correlation with the severity or outcome of COVID-19. (4) Conclusions: Eosinophils and neutrophils expressing eosinophilic surface markers were associated with milder disease and better outcomes of COVID-19, suggesting that a T2 inflammatory response may confer a potential protective effect against the disease.

High Serum S100A12 as a Diagnostic and Prognostic Biomarker for Severity, Multidrug-Resistant Bacteria Superinfection and Herpes Simplex Virus Reactivation in COVID-19

Neutrophils are critical immune cells in severe coronavirus disease 2019 (COVID-19). S100 calcium-binding protein A12 (S100A12) is highly expressed in neutrophils during acute inflammation. The aim of this study was to evaluate serum S100A12 levels as a diagnostic and prognostic tool in COVID-19. Serum samples of patients with moderate and severe COVID-19 were collected during 2020 to 2024. Enzyme-linked immunosorbent assay was used to measure serum S100A12 levels in 63 patients with moderate COVID-19, 60 patients with severe disease and 33 healthy controls. Serum S100A12 levels were elevated in moderate COVID-19 compared to controls and were even higher in severe cases. In moderate disease, serum S100A12 levels positively correlated with immune cell counts. While C-reactive protein and procalcitonin are established inflammation markers, they did not correlate with serum S100A12 levels in either patient cohort. Patients with severe COVID-19 and vancomycin-resistant enterococcus (VRE) infection had increased S100A12 levels. Elevated S100A12 levels were also observed in patients with herpes simplex reactivation. Fungal superinfections did not alter S100A12 levels. These data show that serum S100A12 increases in moderate and severe COVID-19 and is further elevated by VRE bloodstream infection and herpes simplex reactivation. Therefore, S100A12 may serve as a novel biomarker for severe COVID-19 and an early diagnostic indicator for bacterial and viral infections.

Lack of S1PR2 in Macrophage Ameliorates Sepsis-associated Lung Injury through Inducing IL-33-mediated Type 2 Immunity

The function of type 2 immunity and mechanisms underlying the initiation of type 2 immunity after sepsis-induced lung injury remain unclear. Sphingosine-1-phosphate receptor 2 (S1PR2) has been demonstrated to modulate type 2 immunity in the context of asthma and pulmonary fibrosis. Thus, this study aims to investigate the role of type 2 immunity and whether and how S1PR2 regulates type 2 immunity in sepsis. Peripheral type 2 immune responses in patients with sepsis and healthy control subjects were assessed. The impact of S1PR2 on type 2 immunity in patients with sepsis and in a murine model of sepsis was further investigated. The type 2 innate immune responses were significantly increased in the circulation of patients 24 hours after sepsis, which was positively related to clinical complications and negatively correlated with S1PR2 mRNA expression. Animal studies showed that genetic deletion or pharmacological inhibition of S1PR2 induced type 2 innate immunity accumulation in the post-septic lungs. Mechanistically, S1PR2 deficiency promoted macrophage-derived interleukin (IL)-33 increase and the associated type 2 response in the lung. Furthermore, S1PR2-regulated IL-33 from macrophages mitigated lung injury after sepsis in mice. In conclusion, a lack of S1PR2 modulates the type 2 immune response by upregulating IL-33 release from macrophages and alleviates sepsis-induced lung injury. Targeting S1PR2 may have potential therapeutic value for sepsis treatment.