Primitive Macrophages (ExBI)

Primitive macrophages are large, round white blood cells, , which help the body fight off infections by ingesting the disease-causing organism. Primitive macrophages function in phagocytosis and pinocytosis, and serve as antigen presenting cells. Primitive macrophages possess an euchromatic nucleus with large nucleoli, a poorly developed Golgi apparatus, few cytoplasmic organelles, and an abundance of polyribosomes, but are negative for peroxidase activity. They are found in the vascular lumen and in the extravascular mesenchymal layer of the yolk sac.