**Abstract**

Macrophages are immune cells functioning primarily as antigen-presenting cells. They are professional phagocytes and patrol tissues within the body contributing to immunological surveillance. The majority of circulating macrophages and to some extend tissue-resident macrophages differentiate from monocytes. A few of resident macrophages do however originate from embryo during fetal development and remain capable of self-renewal even in adulthood. Macrophages are highly plastic seeing that they play a dual function in inflammatory conditions: either proinflammatory or anti-inflammatory. Depending on state of the body, whether disease, healing or homeostatic state, macrophages can be polarized to either one of two phenotypes-M1 macrophages or M2 macrophages. The former phenotype is associated with pro-inflammatory processes, while the latter mediates anti-inflammatory process. Metabolic process and intermediate substrates influence macrophage activation, polarization and functioning within the body. Moreover, within macrophages themselves, the metabolic pathways activated also influences their polarization. As such inflammatory conditions from either infectious agents or metabolic diseases are a major drive for macrophage activation that determines disease severity and prognosis seemingly because macrophages also activate other immune cells. This interplay between immune system and metabolism is of interest especially in development newer treatment strategies for metabolic diseases and infectious agents.

**Keywords:** immune response, infections, metabolic diseases, metabolism, polarization
