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Chronic inflammation is inflammation which has been of prolonged duration. It is the simultaneous occurrence of active inflammation, tissue destruction and attempts at repair.
Chronic inflammation can either follow on from acute inflammation or it can begin insidiously (a lack of symptoms, the patient is unaware of the onset of the disease with a subtle and cumulative harmfulness) e.g. tuberculosis
Chronic inflammation arises with the following conditions:
- Persistent infections such as those from mycobacteria or certain fungi/parasites. This may cause type IV hypersensitity (delayed-type) but has low toxicity. This is a granulomatous inflammation
- Prolonged exposure to exogenous or endogenous (potentially toxic) agents
- Autoimmunity where auto-antigens evoke a self-perpetuating immune reaction which results in chronic inflammation
The histological features of chronic inflammation:
- Tissue section infiltrated with mononuclear cells (macrophages, lymphocytes, plasma cells)
- There is tissue destruction which has been mainly induced by inflammatory cells
- There are attempts at repair of this tissue, characterised by; connective tissue replacing the damaged tissue, proliferation of small blood vessels (angiogenesis – formation of new blood vessels) and fibrosis