Monocytes emigrate from the blood to a site of injury within 24 to 48 hours after the onset of acute inflammation

and transform into activated macrophages

• Mediate tissue destruction (elastase, collagenase, NO., TNF)

• Phagocytose necrotic cell debris

• Induce fibrosis

Activation of macrophages

Classical pathway

By bacterial endotoxin, T-cell derived signals (IFN-γ), crystals and particulate matter:

- phagocytosis and killing of mycobacteria, borrelia, etc., fungi;

- induction of tissue destruction

Alternative pathway

By cytokines such as IL-4 and IL-13, produced by helper T cells, mast cells and eosinophils:

- fibrosis via elaboration of growth factors (TGF-ß, PDGF, FGF, etc.) which activate fibroblasts ⇒

collagen production

- TGF-ß suppresses acute inflammation

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