Monoamine oxidase A (MAO-A): a signature marker of alternatively activated monocytes/macrophages.

Monocytes/macrophages are versatile cells centrally involved in host defense and immunity. Th1 cytokines induce a classical activation program in monocytes/macrophages leading to a proinflammatory M1 macrophage phenotype while Th2 cytokines IL-4 and IL-13 promote monocyte differentiation into an alternatively activated, anti-inflammatory M2 macrophage phenotype. Although monoamine oxidase A (MAO-A) is primarily known for its action in the nervous system, several recent studies have identified MAO-A as a signature marker of alternative activation of monocytes/macrophages. In this brief review we explore the signaling pathways/molecules that regulate MAO-A expression in alternatively activated monocytes/macrophages. We further discuss the contribution of MAO-A to the resolution of inflammation and identify potential therapeutic targets for controlling inflammation. Altogether this review provides deeper insight into the role of MAO-A in alternative activation of monocytes/macrophages and their participation in the inflammatory response.