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Phagocytosis is a process by which phagocytic cells of innate immunity (macrophages, neutrophils, dendritic cells) destroy foreign bodies and therefore invading pathogens.

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For this, they must first recognize the pathogen through receptors [ PRRs: Pattern Recognition Receptors] (in the shape of a mouth on the gif). These receptors recognize molecular patterns of pathogens [PAMPs: Pathogen Associated Molecular Patterns]. Once the foreign body is recognized, the phagocytic cells must adhere to the pathogens and enclose it in order to ingest it. The pathogen is then trapped in an intracellular vacuole (phagosome). Inside, these cells have lysosomes (small blue spheres on the gif) which are cell organelles containing digestive enzymes. When these lysosomes fuse with the vacuole containing the ingested pathogen (phagolysosome), the enzymes digest the pathogen. Subsequently, the phagocytic cell will present on its surface a small piece (antigen) of the pathogen. They therefore become antigen presenting cells. This will, if necessary, activate other immune cells to strengthen our defences. Finally, they eliminate what cannot be digested. This is how these innate immune cells manage to rid us of these dangers, at least most of the time.

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Immunoglobulins are proteins able to recognise antigens from pathogens and their toxic products. They either form B cell receptors or are secreted (antibodies) by differentiated B cells (plasmocytes). The main roles of antibodies are (i) recognise and neutralise pathogens (ii) activate other immune cells.

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