White blood cells that are produced continuously in the bone marrow and are responsible for removing dead cells and invasive microorganisms
Phagocytes
They carry out a non-specific immune response
There are three main types: neutrophils, macrophages, dendritic cells
Phagocytosis
Recognising and engulfing a pathogen
Neutrophils
Short-lived cells that often leave the blood by squeezing through capillary walls to 'patrol the body tissues
Neutrophil mode of action
1. Chemicals attract neutrophils to site of pathogens
2. Neutrophils move towards pathogens with antibodies attached
3. Neutrophil cell surface membrane extends and engulfs pathogen
4. Neutrophil secretes digestive enzymes into vacuole to destroy pathogen
5. Neutrophils die after killing and digesting pathogens
Macrophages
Larger and longer-lived cells than neutrophils, travel in blood as monocytes then develop into macrophages
Macrophage mode of action
Carry out phagocytosis but do not destroy pathogens completely, instead cut them up and display antigens on their surface as part of an MHC complex to be recognised by lymphocytes
Dendritic cells
Large phagocytic cells with lengthy extensions to interact with pathogens and lymphocytes, transport ingested foreign material to lymph nodes
Antigen-presenting cells
Cells that display antigens from toxins, foreign cells and ingested pathogens on their surface to be recognised by T cells, can be macrophages or body cells invaded by pathogens
Phagosome formation and digestion
Pathogen is engulfed into a phagosome, a lysosome fuses with the phagosome to form a phagolysosome and releases digestive enzymes to destroy the pathogen
