I got a tiny cut on my finger and within half an hour it was warm and it hurt. The following day it was fine but it set me wondering: how fast can our bodies detect an infective agent and slam into defensive action?
• Tissues, such as the epithelium found in skin, have immune cells within them called . These specialised cells can remain in the tissue for years and are activated by tissue damage or invasion by infectious agents. When this occurs, they secrete cytokines which induce inflammation, causing redness, swelling, pain, heat and loss of function in the tissue. This is to help destroy potential pathogens, form a margin around affected areas and recruit more immune cells. The immune response in this regard is instantaneous, although it is also fairly non-specific and the body takes longer (about three days) to start initiating a more specific response to a pathogen.
Jack Leitch, Portsmouth, Hampshire, UK
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• The finger may not have been infected at all. After injury, the body mounts an inflammatory response to initiate healing. The classic signs of inflammation are rubor (redness), dolor (pain) and calor (heat), as recognised by the ancients, and experienced by your correspondent.
Andrew Cooper, Walls, Shetland, UK