What is the difference between active immunity and passive immunity?

Question

The other day our teacher was asking about how our immune system works, and I read in a paper that active immunity is when your body produces its own defense against infections, while passive immunity is when you receive ready-made antibodies from another source. This explanation clearly outlines the differences in how each type is acquired, how long they last, and their roles in protecting against diseases.

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Aino 2025-06-08T06:01:07+00:00 1 Answer 2 views
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  1. fleming
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    2025-06-08T06:04:44+00:00
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    Active Immunity

    Definition:

    Active immunity results when an individual’s own immune system is stimulated to produce antibodies and specialized immune cells (like memory T and B cells) in response to exposure to a specific antigen (e.g., from a pathogen or a vaccine).

    Acquisition:

    Active immunity can be acquired in two ways:

    1. Naturally Acquired Active Immunity: Develops after recovering from a natural infection. The immune system encounters the pathogen, mounts a response, eliminates the infection, and retains immunological memory.
    2. Artificially Acquired Active Immunity: Develops after receiving a vaccine. Vaccines contain antigens (killed or weakened pathogens, subunits, or toxoids) that stimulate an immune response without causing the disease, leading to the production of antibodies and memory cells.

    Mechanism:

    • The individual’s immune system actively participates in generating the response.
    • Involves antigen presentation, T cell activation, B cell activation, antibody production, and the formation of memory lymphocytes.

    Key Characteristics:

    • Requires Exposure to Antigen: Immunity develops only after encountering the specific antigen.
    • Lag Period: There is a delay (typically days to weeks) between initial exposure and the development of protective immunity while the immune response is mounted.
    • Long-Lasting Protection: Immunity is generally durable, often lasting for years or even a lifetime, due to the generation of immunological memory.
    • Memory Response: Subsequent exposure to the same antigen triggers a faster, stronger, and more effective secondary immune response.
    • Self-Generated: Protection is produced by the individual’s own body.

    Examples:

    • Immunity to chickenpox after having the disease.
    • Immunity to measles after receiving the MMR vaccine.

    Passive Immunity

    Definition:

    Passive immunity results from the transfer of pre-formed antibodies or activated immune cells from one individual (or animal) to another, providing immediate but temporary protection without stimulating the recipient’s own immune system.

    Acquisition:

    Passive immunity can also be acquired in two ways:

    1. Naturally Acquired Passive Immunity: Occurs when antibodies are transferred from mother to fetus/infant. IgG antibodies cross the placenta during pregnancy, and IgA antibodies are transferred through breast milk (colostrum), providing protection to the newborn during the first few months of life.
    2. Artificially Acquired Passive Immunity: Involves the administration of pre-formed antibodies (immunoglobulins) obtained from immune humans or animals. This is often used for post-exposure prophylaxis or treatment.

    Mechanism:

    • The recipient’s immune system is passive; it does not generate the antibodies.
    • Protection is conferred directly by the transferred antibodies binding to and neutralizing pathogens or toxins.

    Key Characteristics:

    • No Exposure to Antigen Required (by recipient): Protection is immediate upon transfer of antibodies.
    • Immediate Protection: Immunity is conferred almost instantly.
    • Short-Lived Protection: Protection is temporary, lasting only as long as the transferred antibodies persist (typically weeks to months), as the recipient’s body did not produce them and will eventually degrade them.
    • No Immunological Memory: The recipient’s immune system is not stimulated, so no memory cells are formed, and protection disappears once the transferred antibodies are gone.
    • Externally Generated: Protection comes from an external source.

    Examples:

    • Protection of infants from certain infections due to maternal antibodies.
    • Administration of rabies immunoglobulin after a potential rabies exposure.
    • Use of antitoxin (e.g., diphtheria antitoxin) to treat specific toxin-mediated diseases.
    • Monoclonal antibody therapy for certain viral infections or autoimmune diseases.

    Summary of Key Differences

    Feature Active Immunity Passive Immunity
    Source of Protection Individual’s own immune response Pre-formed antibodies from external source
    Acquisition Method Natural infection or vaccination Maternal transfer or antibody administration
    Onset of Protection Delayed (days/weeks) Immediate
    Duration Long-lasting (years/lifetime) Temporary (weeks/months)
    Immunological Memory Yes, memory cells are generated No, memory cells are not generated
    Recipient’s Role Immune system actively involved Immune system is passive
    Use Case Long-term prevention (vaccination) Immediate protection/treatment (post-exposure)

    Both active and passive immunity play vital roles in protecting individuals from infectious diseases. Active immunity provides durable, long-term protection and is the goal of vaccination programs. Passive immunity offers immediate but temporary protection, crucial in situations where rapid defense is needed or when an individual cannot mount their own effective immune response.

    Source: Janeway’s Immunobiology; Abbas Basic Immunology.

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