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What causes redness, swelling, pain, and fever during inflammation?
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immune system
Stimulation of immune response by activated helper T cells. Activated by complex interaction with molecules on the surface of a macrophage or some other antigen-presenting cell, a helper T cell proliferates into two general subtypes, TH1 and TH2. These in turn stimulate the complex pathways of the cell-mediated immune response and the humoral immune response, respectively.
The four cardinal signs of inflammationāredness, heat, swelling, and paināalong with fever, are driven by complex vascular and chemical responses to tissue injury.1
- Redness and Heat: These occur due to the dilation of small blood vessels and increased blood flow to the site of injury.123
- Swelling (Edema): This is caused by increased blood vessel permeability, which allows fluid, proteins, and white blood cells to accumulate in the tissue outside the blood vessels.12
- Pain: This results from the physical distortion of tissues caused by swelling, as well as the action of chemical mediators such as bradykinin, serotonin, and prostaglandins.14
- Fever: This is a systemic response triggered by chemical mediators, such as pyrogens or interleukins (like IL-1 and IL-6), which act on the hypothalamus in the brain to raise the body's temperature set point.156
These processes are coordinated by various chemical mediators, including histamine, which is released immediately upon injury to trigger vasodilation and increase vascular permeability.4