We compare three similar but different biological effects: provocation-neutralisation treatment of non-antibody-mediated hypersensitivities, hormesis and low-level effects in radiation biology. All three have not yet been fully explained but share some common and interesting properties: non-linear concentration dependence, typical stress pattern and typical immune response. We try to make a generalisation of the three phenomena in terms of the informational properties of the low concentrations, and imply the possible common mechanism.
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