Phagocytes are a major component of the innate immune response, identifying cells with non-self antigens present and ‘phagocytosing’ those cells. This is a highly effective response to pathogens in small numbers, however where a larger dose is administered (or present), this response would be too slow. The activation of complement at the site of infection induces chemotaxis in phagocytic cells, causing them to migrate towards the infection.
Neutrophils can release cytoplasmic granules at the site of infection (containing antimicrobial compounds), phagocytose opsonised cells, and can release neutrophil extracellular traps (NETS, large DNA fibres coated with antimicrobial compounds that are ‘thrown’ around pathogens).
Macrophages are phagocytic cells, engulfing cells not presenting specific self-antigens. Also recruited to the site of infection by chemotaxis, macrophages can release cytokines to recruit other immune cells. Macrophages differentiate into specific cell types in different tissues (monocytes in blood; Kupffer cells in liver; tissue resident macrophages; …).
Phagocytic cells play a crucial role in the initial response to an invading pathogen, helping to combat the initial dose of pathogen and recruit other immune cells through the release of cytokines.