Passive acquired immunity
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Understanding Passive Acquired Immunity
Introduction to Passive Acquired Immunity
Passive acquired immunity refers to the process where antibodies are transferred from one individual to another, providing immediate but temporary protection against pathogens. Unlike active immunity, which involves the body's own immune response to an antigen, passive immunity does not require the recipient's immune system to respond to the antigen directly Marcotte2015Miki1964.
Natural Passive Immunity
Natural passive immunity occurs when antibodies are transferred from mother to child. This can happen in two primary ways:
- Transplacental Transfer: During pregnancy, maternal antibodies cross the placenta to the fetus, providing protection against various infections Marcotte2015Moore2019.
- Breastfeeding: After birth, antibodies present in breast milk, particularly colostrum, are transferred to the infant, offering protection against gastrointestinal pathogens Marcotte2015Moore2019.
These maternal antibodies provide critical protection during the early months of life when the infant's immune system is still developing Marcotte2015Moore2019.
Artificial Passive Immunity
Artificial passive immunity involves the administration of pre-formed antibodies to an individual. This can be achieved through:
- Antibody Preparations: Antibodies derived from the serum or secretions of immunized donors are administered to non-immune individuals. This method is particularly useful for providing immediate protection against specific pathogens Marcotte2015Miki1964.
- Immune Sera: For example, immune sera from virus-like particle (VLP) vaccinated mice have been shown to confer protection against Toxoplasma gondii by inducing a strong antibody response and reducing parasite load .
Artificial passive immunity is especially valuable in cases where individuals are exposed to new or drug-resistant microorganisms, or when they have an impaired immune system that cannot respond effectively to vaccines Marcotte2015Miki1964.
Applications in Disease Protection
Passive immunity has been explored in various contexts:
- Tularemia: Studies have shown that transferring immune tissues, such as spleen cells or peritoneal leucocytes, from recovered donors to normal mice can provide resistance against virulent strains of P. tularensis .
- Listeria monocytogenes: Passive transfer of cells and serum from immune donors has been shown to protect mice against Listeria infection, although the protection was primarily observed with intact living cells from immune donors .
- West Nile Virus (WNV): In a study involving semi-feral ponies, passive transfer of naturally acquired immunity from seroconverted mares to foals was demonstrated, with a significant correlation between mare and foal antibody titers .
Mechanisms and Efficacy
The efficacy of passive immunity depends on several factors:
- Compatibility and Persistence: The transferred antibodies or immune cells must be compatible with the recipient's tissues, and the protection lasts only as long as the antibodies remain active, typically a few months Marcotte2015Moore2019.
- Immune Cell Transfer: The degree of protection can vary based on the immune status of the donor and the number of viable immune cells transferred .
- Immunoglobulin Classes: In the case of Taenia taeniaeformis infection in rats, the protective capacity was found in specific immunoglobulin fractions, particularly 7S immunoglobulins, while other fractions like γM were ineffective .
Conclusion
Passive acquired immunity provides a crucial, albeit temporary, defense mechanism against various pathogens. It can be naturally acquired through maternal antibody transfer or artificially through the administration of pre-formed antibodies. This form of immunity is particularly beneficial in situations where immediate protection is needed, such as exposure to new pathogens, drug-resistant infections, or in individuals with compromised immune systems. Understanding the mechanisms and applications of passive immunity continues to be a vital area of research in immunology.
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