CD68 is a highly glycosylated type I transmembrane glycoprotein predominantly expressed in cells of the monocyte-macrophage lineage, such as macrophages, microglia, and monocytes. It is also known as macrosialin in mice. This protein is mainly localized within the endosomal/lysosomal compartments of these cells and serves as a reliable marker for them. CD68 plays a crucial role in various immune processes, including phagocytosis, antigen presentation, and the regulation of immune responses. It is involved in the clearance of cellular debris, foreign substances, microbes, and even cancer cells. In different tissues, CD68-positive cells perform diverse functions. For example, in the liver, CD68 is expressed in Kupffer cells that filter blood and remove pathogens; in the lungs, alveolar macrophages with high CD68 levels maintain pulmonary homeostasis. Additionally, CD68 is notable in the central nervous system, where microglia express this marker to maintain neural health by clearing debris and modulating inflammatory responses.