Role of plant-derived natural compounds in macrophage polarization

Macrophages are important cells of the immune system and are sufficiently plastic to polarize either an M1 state or M2 state. Depending on the signals received from different intrinsic or extrinsic factors, the macrophage polarity is determined. These cells are distributed in every tissue of the body and are also found as circulating cells in the bloodstream called ‘monocytes’. Natural products may be one extrinsic factor to modulate macrophage polarization. It is important to understand the mechanism by which natural products drive the polarization of macrophages. Based on recent advancements in the understanding of immunology, macrophages are classified as classically activated and alternatively activated, also designated as M1 and M2 macrophages respectively. The resident brain macrophages (microglia) get activated under stress and attain the M1 macrophage phenotype which is related to inflammatory mechanisms leading to neurodegeneration while treatment with plant-derived natural compounds drives the M1 microglia towards the M2 type which prevents the inflammatory response and protects the neurons. Understanding the mechanism of polarization of macrophages by natural compounds will be useful in treating different types of inflammatory diseases including Alzheimer’s and Parkinson’s. In this review, we summarized the current understanding of macrophage polarization using plant-derived natural compounds and their ability to regulate the pathophysiology of the tissues.