Overview
The acute phase response is a facet of the innate immune system that occurs in response to infection, trauma or other insults. Certain mediators, known as acute phase reactants, are increased or decreased in the context of acute inflammation. These markers are commonly measured in clinical practice as indicators of acute illness.
Pathogenesis
The acute phase response is predominantly mediated by the pro-inflammatory cytokines tumour necrosis factor (TNF), interleukin 1 (IL-1) and interleukin 6 (IL-6) secreted by macrophages and other immune cells.
Causes of Acute Phase Response
- Infection - bacterial, viral, fungal, parasitic
- Tissue infarction - e.g. myocardial infarction, renal infarction, splenic infarction, acute limb ischaemia
- Exogenous substances (i.e. foreign bodies)
- Endogenous substances - uric acid crystals, calcium pyrophosphate crystals
- Autoimmune disease
- Allergies
- Neoplasia
- Trauma
- Surgery
- Burns
Manifestations
Clinical Features
- Fever
- Rigors
- Tachycardia
Severe Cases
- Distributive shock
- Disseminated intravascular coagulation
Acute Phase Reactants
Positive Acute Phase Reactants (increase)
- C-reactive protein (CRP)
- Fibrinogen
- Ferritin
- Hepcidin
- Haptoglobin
- Caeruloplasmin
- Complement proteins C3 / C4
- Serum amyloid A (not measured)
Negative Acute Phase Reactants (decrease)
- Serum albumin
- Transferrin
- Alpha-foetoprotein
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