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Understanding the differences between passive and active immunity is crucial for students preparing for USMLE Step 1. Below is a comparison of these two immune responses, highlighting key features and examples.
Feature | Passive Immunity | Active Immunity |
---|---|---|
Means of Acquisition | Receiving preformed antibodies | Exposure to exogenous antigens (e.g., infection, vaccination) |
Onset | Rapid (immediate protection) | Slow (takes time to develop immune response) |
Duration | Short-lasting (antibodies have a short half-life, ~3 weeks) | Long-lasting (includes memory, providing long-term protection) |
Examples | IgA in breast milk, maternal IgG crossing placenta, antitoxins, humanized monoclonal antibodies | Natural infection, vaccines, toxoids |
Special Notes | After exposure to certain toxins (e.g., tetanus, rabies), preformed antibodies can be administered | Natural infections or vaccines induce the body’s immune system to produce antibodies |