Alveolar macrophage, coloured scanning electron micrograph (SEM). Sucrose fix of a rat alveolar macrophage and three micrometre particle phagocytosis. A tissue macrophage is a large, mature phagocyte that can ingest and destroy invading microbes, foreign particles, cancerous or diseased cells and cellular debris. Alveolar (lung pleural cavity) macrophages are part of the reticuloendothelial system. Magnification: x1,400 when shortest axis printed at 25 millimetres.