Understanding the Mysterious Macrophages

Macrophages are a type of white blood cells located in peripheral blood and inflamed tissues. In animals, it mainly participates in non-specific immune regulation (innate immunity) through phagocytosis of bacteria, dead cells and cell debris, and then digests the phagocytized material and presents its characteristics to subsequent lymphocytes and other immune cells to participate in specific immunity modulation (acquired immunity).

The precursors of macrophages are monocytes that hail from the bone marrow, traveling all around the bloodstream, waiting to migrate to the tissues to differentiate into macrophages. These macrophages are omnipresent, found in every nook and cranny of the body. However, they prefer to flock around the body's external areas, such as the lungs, the gastrointestinal tract, and the skin.

Classification of Macrophages

Macrophages can be classified based on their location and function. The two main types of macrophages are resident and inflammatory macrophages. Resident macrophages, as the name suggests, are a permanent fixture of tissues and organs throughout the body, helping out with tissue maintenance, repair, and removing the unsightly dead cells and debris that nobody wants to see. On the other hand, inflammatory macrophages are produced in response to infections or injuries, kind of like a specialized task force.

Inflammatory macrophages have their own subtypes, namely classically activated macrophages (M1) and alternatively activated macrophages (M2). M1 macrophages mainly function in the body to phagocytize foreign substances such as bacteria and endogenous substances such as apoptotic cell debris, and to protect tissues and organs from foreign substances. In inflammatory diseases, M1 macrophages are enriched in early inflammatory sites and activated by pro-inflammatory factors such as LPS, TNFα, IFNγ, and then promote the occurrence and development of inflammation by secreting inflammatory factors such as IL12 to protect the body's immune system. Invasion by foreign substances.

In the late stage of inflammation, M2 macrophages play a role in inhibiting inflammation, repairing tissue, and rebuilding tissue structure. During the inflammatory response, the M1/M2 macrophage population ratio changes over time, eventually eliminating the effects of inflammation completely. In some chronic inflammation and specific acute inflammatory processes, the ratio of M1/M2 cell populations is out of balance, and excessive activation of M1 cell populations can lead to severe tissue damage and subsequent adverse symptoms such as more severe inflammatory factor storms.

Identification and Characterization of Macrophages

Macrophages are highly plastic, capable of changing their phenotype in response to environmental cues. This results in distinct subpopulations of macrophage types, each with distinct gene expression profiles and cellular functions. Macrophages can be identified using a variety of markers, including cell surface receptors and intracellular proteins. One of the most commonly used markers for macrophages is CD68, which is a glycoprotein that is found on the surface of macrophages and other phagocytic cells. The table below lists other common markers that can be used to identify and characterize macrophages.