Elevated Calprotectin and Abnormal Myeloid Cell Subsets Discriminate Severe from Mild COVID-19

Area of Science:

• Immunology
• Hematology
• Virology

Background:

• Dysregulation of blood myeloid cells is observed in COVID-19.
• The relationship between innate myeloid response, disease severity, and high-risk patient discrimination in COVID-19 remains unclear.

Purpose of the Study:

• To investigate differences in innate myeloid cell response based on COVID-19 severity.
• To determine if innate immunity markers can identify high-risk COVID-19 patients.

Main Methods:

• High-dimensional flow cytometry and single-cell RNA sequencing were used on peripheral blood cells from COVID-19 patients.
• Analysis focused on monocyte and neutrophil populations and their associated markers.

Main Results:

• Severe COVID-19 cases showed decreased non-classical monocytes (CD14LowCD16High) and accumulated HLA-DRLow classical monocytes.
• Massive calprotectin release (S100A8/S100A9) and immature, immunosuppressive neutrophils (CD10LowCD101-CXCR4+/-) were detected in severe cases, suggesting emergency myelopoiesis.
• Calprotectin plasma levels and reduced non-classical monocyte frequencies could distinguish severe COVID-19 patients.

Conclusions:

• Specific alterations in myeloid cell populations and calprotectin levels characterize severe COVID-19.
• Calprotectin and monocyte frequency show potential as predictive biomarkers for severe COVID-19, warranting further prospective studies.