Abstract
Macrophages are professional antigen-presenting cells and serve as the first line of defense against invading pathogens. Macrophages are polarized toward the proinflammatory classical (M1) or anti-inflammatory alternative (M2) phenotype upon viral infections. M1-polarized macrophages exert critical roles in antiviral responses via different mechanisms. Within the long competitive history between viruses and hosts, viruses have evolved various immune evasion strategies, inhibiting macrophage acquisition of an antiviral phenotype, impairing the antiviral responses of activated macrophages, and/or exploiting macrophage phenotypes for efficient replication. This review focuses on the sophisticated regulation of macrophage polarization utilized by viruses and is expected to provide systematic insights into the regulatory mechanisms of macrophage polarization by viruses and further facilitate the design of therapeutic targets for antivirals.
Highlights
In the battle against viruses, immune cells, including macrophages, are essential fighters that directly kill viruses or secrete antiviral factors
This review presents an overview of the sophisticated regulation of macrophage polarization and focuses on the multiple immune evasion and exploitation mechanisms leveraged by various viruses against the antiviral responses of polarized macrophages
Macrophages are polarized into the proinflammatory (M1) or anti-inflammatory (M2) phenotype upon exposure to diverse stimuli
Summary
In the battle against viruses, immune cells, including macrophages, are essential fighters that directly kill viruses or secrete antiviral factors. Upon inflammation, circulating monocytes in peripheral blood migrate into different tissues and are differentiated into several types of macrophages, such as microglia (central nervous system), alveolar macrophages (lung), Kupffer cells (liver), histocytes (spleen), and osteoclasts (bone marrow) (Epelman et al, 2014; Shapouri-Moghaddam et al, 2018). Macrophage activation is known as polarization (Sang et al, 2015). Viruses have evolved multiple strategies to counteract the antiviral responses elicited by M1 macrophages and take advantage of M2-polarized macrophages for efficient replication (Sang et al, 2015)
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