Most cells can take up small volumes of culture medium by a process termed pinocytosis.
Some cells can take up small particulate matter by surrounding the particle with extrusions of the cell membrane by a process termed phagocytosis.
Macrophages excel at phagocytosis. Macrophages in culture will phagocytose a whole range of different particles from small latex beads to polymer beads twice their own diameter.
Macrophages recognise and take up apoptotic and necrotic cells, bringing about their efficient removal.
Macrophage phagocytosis of micro-organisms is important in host immunity and activated macrophages kill ingested pathogens by production of reactive oxygen and nitrogen metabolites. Medically important pathogens including the mycobacteria which cause tuberculosis and leprosy evade immune destruction by surviving inside the macrophage. Survival of pathogens in macrophages is central to the pathogenesis and tissue injury in these important human diseases.
The photomicrographs below show a human macrophage engulfing and internalising the yeast Candida albicans.
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