Introduction
- Passive immunity is unique in that the recipient does not produce an immune response or generate their antibodies or sensitized cells.
- Instead, they receive preformed antibodies or sensitized lymphocytes from an immunized host.
- This mode of immunity does not involve the production of memory cells or the establishment of primary or secondary responses.
Types of Passive Immunity
- Passive immunity can be classified into two main types: natural and artificial.
Natural Passive Immunity
- Natural passive immunity refers to the development of resistance in a fetus or newborn through the transfer of antibodies from the mother. In human beings, this transfer predominantly occurs via the placenta during the later stages of pregnancy.
- The antibodies that cross the placenta are primarily immunoglobulin G (IgG), while other immunoglobulin subtypes such as A, D, E, and M do not traverse the placental barrier.
- In addition to placental transfer, other mammals, such as pigs, transfer antibodies orally through colostrum—the first milk produced by the mother after giving birth.
- Colostrum is rich in IgA antibodies, which can protect newborns against intestinal infections.
- Breastfed babies can directly absorb these immunoglobulins through the gastrointestinal system, further enhancing their passive immunity.
- It is important to note that bottle-fed babies do not benefit from this natural mechanism and are thus encouraged to be breastfed.
- During the first three months of life, the baby’s immune system is not fully developed.
- However, the maternal antibodies acquired through the placenta offer protection against various infections until the baby can synthesize IgM, which typically occurs around five months of age.
- Notably, if the mother undergoes active immunization during pregnancy, the passive immunity acquired by the child is significantly enhanced.
- For instance, pregnant mothers in areas where neonatal tetanus is prevalent receive tetanus toxoids to ensure the newborn is immune to tetanus.
Artificial Passive Immunity
- Artificial passive immunity involves the development of resistance in a patient through the transfer of antibodies or immunized lymphocytes from a donor.
- This type of immunity is therapeutically used to treat conditions such as tetanus, diphtheria, gas gangrene, snake bites, and immunodeficiency diseases.
- Artificial passive immunity can be achieved through several methods:
- Hyperimmune Serum of Animal or Human Origin:
- Hyperimmune serum is derived from immunized humans or animals by repeatedly injecting an antigen.
- For example, anti-tetanus serum (ATS) is prepared by administering tetanus toxoid to horses and collecting their serum.
- The antibodies in the serum are then concentrated and purified for use.
- ATS can be administered subcutaneously for prophylaxis or intravenously for the treatment of tetanus.
- However, due to potential severe hypersensitivity reactions, the use of animal-derived antisera has been limited.
- To mitigate this, human ATS is now prepared by hyperimmunizing human volunteers with tetanus toxoid, resulting in longer-lasting immunity compared to horse serum.
- Convalescent Serum:
- Convalescent serum is collected from individuals who have recovered from a particular infectious disease.
- This serum contains a high concentration of antibodies specific to the antigen responsible for the disease.
- Convalescent serum is commonly used for passive immunization against viral infections such as measles and rubella.
- Pooled Sera from Different Healthy Individuals:
- Healthy adults’ sera contain antibodies against common infectious microorganisms in the community.
- Pooled sera from a large number of healthy individuals are collected, and the antibody fraction is used for passive immunization against prevalent infectious diseases in that community.
- Combined Immunization:
- Combined immunization involves the simultaneous use of both active and passive methods to achieve immediate and long-lasting protection.
- This approach is employed in emergency situations where immediate defense is necessary.
- For instance, if a non-immune person sustains a tetanus-prone wound, they may receive ATS for immediate protection while simultaneously receiving a course of tetanus toxoid to induce active immunity for sustained defense.
- Adoptive Immunity:
- Adoptive immunity involves the injection of immunologically competent lymphocytes to confer passive immunity.
- This method is used in the treatment of tuberculosis and leprosy.
Conclusion
- Passive immunity plays a significant role in protecting individuals from infections and diseases. Whether acquired naturally through the transfer of antibodies from mother to child or artificially through medical interventions, passive immunity offers immediate defense in critical situations. However, it is essential to remember that passive immunity is temporary and cannot provide long-term protection. Active immunity, achieved through vaccinations, is the key to establishing a robust and enduring defense against pathogens. By understanding the intricacies of passive immunity and its applications, we can make informed decisions to protect ourselves and others from infectious diseases.
FAQs
Q1: How long does passive immunity last? Passive immunity is temporary and typically lasts for a few days or weeks.
Q2: Can passive immunity be transferred through breast milk? Yes, breastfeeding provides natural passive immunity to newborns as they receive immunoglobulins from their mother’s colostrum.
Q3: Is passive immunity better than active immunity? Passive immunity offers immediate protection but is temporary. Active immunity, achieved through vaccinations, provides long-term and robust defense against infections.
Q4: What are some examples of diseases treated with artificial passive immunity? Artificial passive immunity is used to treat diseases such as tetanus, diphtheria, gas gangrene, snake bites, and immunodeficiency diseases.
Q5: How is artificial passive immunity achieved? Artificial passive immunity can be achieved through methods such as hyperimmune serum, convalescent serum, pooled sera from different individuals, combined immunization, and adoptive immunity.