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A macrophage is a type of white blood cell that plays a crucial role in the immune system. These large phagocytic cells are derived from monocytes, which are produced in the bone marrow and circulate in the bloodstream before migrating into tissues where they mature into macrophages.

The primary function of macrophages is to engulf and digest cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the specific markers of healthy body cells. This process, known as phagocytosis, helps maintain tissue homeostasis and provides a first line of defense against pathogens. Macrophages can吞噬 dead or damaged cells, bacteria, viruses, and other harmful particles, breaking them down using enzymes within specialized compartments called lysosomes.

These versatile immune cells are found throughout the body in various tissues, where they are given specific names based on their location. For example, Kupffer cells in the liver, microglia in the brain, and alveolar macrophages in the lungs. Tissue-resident macrophages can self-renew and maintain their populations independently of circulating monocytes under steady-state conditions.

Beyond their phagocytic abilities, macrophages serve as important antigen-presenting cells that help activate other components of the immune system. They process foreign antigens and display them on their surface to T cells, bridging innate and adaptive immunity. Macrophages also produce various signaling molecules called cytokines that regulate inflammation and immune responses.

Macrophages exhibit remarkable plasticity and can adapt their functional phenotype based on environmental cues. They are broadly classified into two main activation states: classically activated (M1) macrophages that promote inflammation and pathogen killing, and alternatively activated (M2) macrophages that support tissue repair and resolution of inflammation.

Dysfunction or improper activation of macrophages has been implicated in various diseases including chronic inflammation, autoimmune disorders, cancer, and metabolic diseases like atherosclerosis and diabetes.