Explain that passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual, including across the placenta and in breast milk

Passive immunity is a short-term defense mechanism against pathogens that occurs when antibodies are acquired from another individual rather than being produced by the recipient’s own immune system. This type of immunity can occur naturally or artificially and is characterized by its immediate but temporary protective effects.

Key Features of Passive Immunity

1. Acquisition of Antibodies:
   • Natural Passive Immunity: This occurs when antibodies are transferred from one individual to another through natural means. A common example is the transfer of maternal antibodies to a fetus during pregnancy. Antibodies, particularly Immunoglobulin G (IgG), cross the placenta and provide the unborn child with protection against infections during the early months of life.
   • Breast Milk: After birth, antibodies are also transferred through breast milk, especially in the form of colostrum, which is rich in antibodies. This provides infants with additional protection against pathogens they may encounter.
2. Immediate Protection:
   • Passive immunity offers immediate defense against pathogens because the antibodies are pre-formed and ready to act upon introduction into the body. This is particularly beneficial in situations where rapid protection is necessary, such as after exposure to certain infectious diseases or toxins.
3. Short Duration:
   • The protection provided by passive immunity is temporary, typically lasting only a few weeks to a few months. This is because the recipient’s immune system does not produce memory cells or generate a lasting immune response; instead, the borrowed antibodies gradually degrade over time.
4. Examples of Passive Immunity:
   • Maternal Transfer: As mentioned, maternal antibodies are passed to the fetus through the placenta and to infants through breast milk, offering crucial early-life protection.
   • Artificial Passive Immunity: This can be achieved through medical interventions, such as administering immunoglobulin therapy, where antibodies derived from human or animal sources are given to individuals at risk of infection or those unable to produce their own antibodies.