Passive immunity

Type of immunity acquired by the transfer of antibodies

Passive immunity
Diphtheria antitoxin, an example of passive immunity
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Passive immunity is a form of immunity that occurs when antibodies are transferred from one individual to another. This type of immunity provides immediate protection against disease, but it is temporary, as the antibodies are eventually degraded and not replaced. Passive immunity can be acquired naturally or artificially.

Types of Passive Immunity

Natural Passive Immunity

Natural passive immunity occurs when antibodies are transferred from mother to child. This can happen in two main ways:

• Transplacental Transfer: During pregnancy, maternal antibodies are transferred to the fetus through the placenta. This provides the newborn with protection against infections during the early months of life.
• Breastfeeding: Antibodies, particularly IgA, are present in breast milk and can provide additional protection to the infant against gastrointestinal infections.

Artificial Passive Immunity

Artificial passive immunity involves the transfer of antibodies from an external source. This can be achieved through:

• Antiserum or Antitoxin Administration: Antibodies are collected from the serum of immune individuals or animals and administered to a non-immune person. For example, diphtheria antitoxin is derived from horse serum and used to treat diphtheria infections.

Administration of diphtheria antitoxin derived from horse serum

• Monoclonal Antibodies: These are laboratory-produced molecules engineered to serve as substitute antibodies. They can restore, enhance, or mimic the immune system's attack on cells.

Applications of Passive Immunity

Passive immunity is used in several clinical situations:

• Post-exposure Prophylaxis: After exposure to certain diseases, such as rabies or hepatitis B, passive immunity can provide immediate protection.
• Immunocompromised Patients: Individuals with weakened immune systems may receive passive immunity to help fight infections.
• Treatment of Acute Infections: In some cases, passive immunity is used to treat acute infections, such as tetanus or botulism.

Advantages and Disadvantages

Advantages

• Provides immediate protection against pathogens.
• Useful in individuals who cannot produce an adequate immune response.

Disadvantages

• Temporary protection, as antibodies are eventually degraded.
• Risk of allergic reactions or serum sickness, especially with animal-derived antibodies.

Also see

• Active immunity
• Immunization
• Antibody
• Immune system