Induction and duration of immunological tolerance depend on the dose and repetition of antigen exposure.
Dose-dependent induction
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Tolerance is not induced below a threshold antigen dose. Further increases in dose increase the duration of tolerance.
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For certain antigens, both high and low doses induce tolerance, termed high zone and low zone tolerance respectively. Intermediate doses produce immunity instead.
Forms and persistence
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Felton’s immunological paralysis is a special type of high zone tolerance.
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The duration of tolerance is variable and can be prolonged by repeated tolerogenic stimuli.