Monitoring Macrophage Polarization in Infectious Disease, Lesson From SARS‐CoV‐2 Infection

ABSTRACT The concept of macrophage polarization has been largely used in human diseases to define a typology of activation of myeloid cells reminiscent of lymphocyte functional subsets. In COVID‐19, several studies have investigated myeloid compartment dysregulation and macrophage polarization as an indicator of disease prognosis and monitoring. SARS‐CoV‐2 induces an in vitro activation state in monocytes and macrophages that does not match the polarization categories in most studies. In COVID‐19 patients, monocytes and macrophages are activated but they do not show a polarization profile. Therefore, the investigation of polarization under basic conditions was not relevant to assess monocyte and macrophage activation. The analysis of monocytes and macrophages with high‐throughput methods has allowed the identification of new functional subsets in the context of COVID‐19. This approach proposes an innovative stratification of myeloid cell activation. These new functional subsets of myeloid cells would be better biomarkers to assess the risk of complications in COVID‐19, reserving the concept of polarization for pharmacological programme evaluation. This review reappraises the polarization of monocytes and macrophages in viral infections, particularly in COVID‐19.