Expansion
Neutrophils first, macrophages next, lymphocytes for the long term
Expansion
The sequence
- Neutrophils - arrive within minutes to hours, peak at 24 hours, and are short lived. Phagocytosis and the respiratory burst
- Macrophages - dominate after 48 hours. Phagocytosis, antigen presentation, cytokine release, and orchestration of repair. Become epithelioid cells and giant cells in granulomas
- Lymphocytes and plasma cells - the hallmark of chronic inflammation. Plasma cells produce antibody
- Eosinophils - parasites and allergy
- Mast cells and basophils - histamine, immediate hypersensitivity
“Neutrophils are the infantry, macrophages the engineers, lymphocytes the occupation.”
Neutrophil emigration follows four steps: margination, rolling (selectins), adhesion (integrins) and transmigration, then chemotaxis along a gradient of C5a, LTB4, IL-8 and bacterial peptides.
Leucocyte adhesion deficiency proves the sequence: defective integrins mean neutrophils cannot adhere, so there is a marked neutrophilia in the blood with no pus at the site of infection, and delayed umbilical cord separation.
Granulomatous inflammation is a distinct chronic pattern in which macrophages become epithelioid and wall off a stimulus that cannot be eliminated.