Types of Adaptive Immunity
Adaptive immunity can be classified into two main types: active and passive. Both types can be acquired either naturally or artificially.
Active Immunity
Active immunity occurs when the immune system is exposed to a pathogen and produces its own antibodies and memory cells. This can happen through natural exposure to an infection or through vaccination.
Naturally Acquired Active Immunity:
- Mechanism: The body encounters a pathogen naturally (e.g., through infection) and mounts an immune response.
- Process: The immune system produces antibodies and activates memory cells specific to the pathogen.
- Duration: Generally long-lasting; memory cells remain in the body for years, providing prolonged protection against future infections by the same pathogen.
- Examples: Recovery from diseases like chickenpox or measles.
Artificially Acquired Active Immunity:
- Mechanism: Immunity is gained through vaccination. Vaccines contain antigens that stimulate the immune system to produce antibodies and memory cells without causing the disease.
- Process: The vaccine introduces a weakened or inactivated form of the pathogen or its components to elicit an immune response.
- Duration: Long-lasting, similar to natural active immunity, with booster doses sometimes required to maintain immunity.
- Examples: Vaccines for polio, influenza and COVID-19.
Passive Immunity
Passive immunity occurs when antibodies are transferred from one individual to another, providing temporary protection. This can happen naturally through maternal transfer or artificially through antibody injections.
Naturally Acquired Passive Immunity:
- Mechanism: Antibodies are transferred from mother to infant during pregnancy or breastfeeding.
- Process: Immunoglobulins (antibodies) cross the placenta or are present in breast milk and provide immediate protection to the infant.
- Duration: Short-lived; typically lasts for a few months to a year, as the transferred antibodies gradually degrade and are not replaced by the infant’s immune system.
- Examples: Antibodies from the mother protecting the newborn from infections.
Artificially Acquired Passive Immunity:
- Mechanism: Antibodies are injected into an individual, often as part of a treatment for specific infections or conditions.
- Process: Antiserum or immune globulin containing preformed antibodies is administered to provide immediate protection or treatment.
- Duration: Short-term; immunity lasts until the injected antibodies are broken down by the body.
- Examples: Administration of antivenom for snake bites, immune globulin injections for hepatitis exposure.
