Macrophage. Coloured transmission electron micrograph (TEM) of a macrophage cell. The cell's nucleus is bright green. Mitochondria (green) in the cell's cytoplasm produce energy for the cell. Lysosomes (red) contain enzymes for digesting foreign particles. Macrophages are a type of large white blood cell that are found in tissues rather than circulating in the blood. They recognise foreign particles, including bacteria, pollen and dust, and phagocytose (engulf) and digest them.