Passive Immunity – Definition, Types, Characteristics, Examples

What is Passive Immunity?

• Passive immunity refers to the acquisition of temporary protection against infectious diseases through the introduction of antibodies produced outside the body. Unlike active immunity, which is developed by the body’s own immune system, passive immunity involves the administration of pre-formed antibodies from an external source, such as through vaccines or immune serum.
• The antibodies provided in passive immunity act as a form of therapy, offering immediate defense against specific pathogens. These antibodies can be thought of as “loaned” antibodies since they are not produced by the individual’s own immune system. The borrowed antibodies help prevent or fight certain infectious diseases, providing a quick response to the infection.
• One common example of passive immunity is the emergency use of immune serum for treating snake or scorpion bite victims. The immune serum contains antibodies specifically targeted against the venom, offering immediate protection until the individual’s immune system can generate its own response. In this case, passive immunity is transferred between individuals because the person receiving the treatment does not produce their own immune response against the pathogen.
• Passive immunity also plays a significant role in newborn infants. Maternal antibodies are transferred to the developing fetus during pregnancy, providing temporary protection against various infections. These maternal antibodies circulate in the newborn’s system, safeguarding them until their own immune system matures.
• Passive immunity can also be used as a preventive measure, known as prophylaxis, for individuals with compromised immune systems or those who anticipate future exposure to a particular microbe. By introducing antibodies from an external source, the immune potential of these individuals can be boosted, offering them temporary protection.
• It’s important to note that passive immunity has limitations. The protection it provides is short-lived, typically lasting a few weeks or months, as the administered antibodies are gradually cleared from the body. Unlike active immunity, where the body’s immune cells produce antibodies continuously, passive immunity does not transfer the cells responsible for antibody production. Therefore, the individual does not develop a long-term immune response to the pathogen.
• In summary, passive immunity involves the introduction of pre-formed antibodies from an external source to provide immediate protection against specific pathogens. It is a temporary form of immunity that can be beneficial in certain situations, such as emergency treatments or providing temporary protection to newborns or individuals with compromised immune systems. However, its effects are limited in duration, as the borrowed antibodies are gradually eliminated from the body, and it does not stimulate the individual’s own immune system to produce long-term protection.

Definition of Passive Immunity 

Passive immunity is the temporary protection against infectious diseases provided by the introduction of pre-formed antibodies from an external source, rather than the body’s own immune response.

Characteristics of Passive Immunity

Passive immunity possesses several distinct characteristics that differentiate it from active immunity:

1. Exogenous Source: Passive immunity is acquired from an external source, such as through the administration of pre-formed antibodies or immune serum. It does not require the individual to be exposed to the infectious agent or its antigen directly. This makes passive immunity particularly useful in situations where immediate protection is needed.
2. Immediate Response: One of the key advantages of passive immunity is its rapid action. Since pre-formed antibodies are introduced into the body, there is no delay in the immune response. The antibodies are already available to recognize and neutralize the pathogens, providing immediate defense against infection.
3. Temporary Protection: While passive immunity offers quick protection, its effects are temporary and short-lived compared to active immunity. The borrowed antibodies gradually diminish or get cleared from the body over time. Depending on the specific circumstances, passive immunity can last for a few days, weeks, or months. After this period, the individual’s own immune system needs to generate a response for sustained protection.
4. Serum Sickness: One potential drawback of passive immunity is the risk of serum sickness. Serum sickness can occur when the individual’s immune system reacts to the foreign antibodies introduced into the body. This immune reaction can lead to symptoms such as fever, rash, joint pain, and even more severe complications in some cases. It’s important to monitor for such reactions and administer passive immunity treatments under appropriate medical supervision.

Types of Passive Immunity

Passive immunity may be natural or artificial. 

1. Natural passive immunity

• Natural passive immunity refers to the transfer of antibodies from a mother to her offspring during pregnancy or through breastfeeding. This transfer of antibodies provides temporary protection to the newborn against certain infections. There are two primary mechanisms through which natural passive immunity occurs: the transfer of IgG antibodies during pregnancy and the transfer of IgA antibodies through breastfeeding.
• During pregnancy, maternal antibodies of the IgG class pass from the mother’s bloodstream into the fetal bloodstream through the placenta. This transfer is crucial in providing immune protection to the developing fetus. One notable example is the prevention of neonatal tetanus. To achieve this, pregnant mothers are actively immunized by administering tetanus toxoid. This vaccination induces the mother’s immune system to produce high levels of antibodies against the tetanus toxin. These antibodies are then transmitted to the fetus through the placenta, offering protection against tetanus after birth. In the case of first-time mothers, multiple doses of the tetanus toxoid are typically administered during pregnancy, while for second-time mothers, it is often given during the last trimester.
• In addition to IgG transfer during pregnancy, natural passive immunity is also observed through the passing of IgA antibodies from the mother to the newborn through breastfeeding. IgA antibodies are present in breast milk and play a vital role in providing localized protection against infections in the mucosal surfaces of the baby, primarily in the respiratory and gastrointestinal tracts. These antibodies help defend the newborn against pathogens they may encounter during breastfeeding, reducing the risk of infections.
• Natural passive immunity is an important natural defense mechanism that helps protect newborns during their early stages of life. The transfer of maternal antibodies, both during pregnancy and through breastfeeding, provides temporary immune protection to the infant until their own immune system matures and can generate its own immune responses.

2. Artificial passive immunity

Artificial passive immunity refers to the deliberate administration of pre-formed antibodies to provide immediate protection against specific pathogens or toxins. Here are some key points about artificial passive immunity:

1. Administration: Artificial passive immunization is typically carried out through injection. The pre-formed antibodies, in the form of antiserum, are directly introduced into the individual’s bloodstream.
2. Outbreak Response and Emergency Treatment: Artificial passive immunity is employed in situations such as recent disease outbreaks or as an emergency treatment for toxicity. It provides immediate protection while the individual’s own immune system mounts a response.
3. Preformed Antibodies: In artificial passive immunity, preformed antibodies raised against a specific infecting agent are administered. These antibodies can be produced in animals, known as serum therapy, but there is a risk of anaphylactic shock due to an immune response against animal serum. Whenever possible, humanized antibodies produced in vitro through cell culture are used to mitigate this risk.
4. Neutralizing Toxins and Preventing Replication: The administration of antisera containing preformed antibodies allows a large quantity of antibodies to be available in the recipient’s body. These antibodies can neutralize the action of toxins produced by pathogens. In the case of viral infections such as rabies, hepatitis A and B, administration of specific antibodies during the incubation period can prevent viral replication and alter the course of the infection.
5. Advantages and Disadvantages: The main advantage of artificial passive immunity is the immediate availability of a large number of antibodies, providing instant protection. However, there are two notable disadvantages. First, the lifespan of these preformed antibodies is relatively short, so their protective effects are temporary. Second, there is a possibility of hypersensitivity reactions, particularly if antibodies derived from other animal species are given to individuals who are hypersensitive to those animals’ globulins. This can lead to conditions such as serum sickness.

Applications of Passive Immunity

Passive immunity, utilizing antibody therapy, has various applications in the field of medicine. Some key applications include:

1. Treatment of Specific Diseases: Antibodies can be used to treat patients who are already sick with certain diseases. For example, patients with diphtheria or cytomegalovirus can be treated with specific antibodies to neutralize the pathogen and aid in recovery.
2. Prevention of Infectious Diseases: Passive immunization can serve as a preventive measure when individuals are exposed to pathogens. By administering antibodies, the development of an illness can be halted or mitigated. This approach is commonly used for diseases such as respiratory syncytial virus (RSV), measles, tetanus, hepatitis A and B, rabies, and chickenpox.
3. Benefits for High-Risk Individuals: While passive immunization can be beneficial for all individuals, it holds particular value for high-risk individuals, especially those with immune deficiencies. These individuals may have compromised immune systems, making it difficult for them to mount an effective immune response to pathogens. Antibody therapy can provide them with immediate protection and help prevent severe illness.
4. Emergency Situations: Passive immunity can be crucial in emergency situations, such as bioterrorism attacks or outbreaks of infectious diseases. It offers rapid protection when time is of the essence, providing a quick defense against harmful pathogens.
5. Complementing Active Immunization: Passive immunity can complement active immunization strategies. In some cases, individuals may require immediate protection before their immune system has a chance to respond to a vaccine. Passive immunization can bridge this gap and offer immediate temporary protection until active immunity develops.

Future of Passive Immunization

The future of passive immunization holds promising developments and potential applications. Here are two key aspects:

1. Monoclonal Antibodies (MAbs): The technology for producing monoclonal antibodies is advancing, enabling the production of pure antibodies that target specific sites on pathogens. MAbs have broad applications in infectious diseases and other medical conditions. Currently, there is one commercially available MAb treatment for preventing severe disease caused by respiratory syncytial virus (RSV) in high-risk infants. Additionally, MAbs are increasingly being used by physicians to combat noninfectious diseases, including cancer, multiple sclerosis, rheumatoid arthritis, Crohn’s disease, and cardiovascular disease. Researchers are exploring new technologies for antibody production, such as recombinant systems using yeast cells or viruses, as well as systems that combine human cells and mouse cells or human DNA and mouse DNA. These advancements hold potential for further expanding the range and effectiveness of monoclonal antibody therapies.
2. Bioterror Threats: Passive immunization can play a crucial role in responding to bioterrorism attacks involving infectious biological agents. In such emergency situations, the immediate protection provided by antibodies is advantageous compared to vaccines, which may require time to induce immunity or necessitate booster doses. Various potential bioterror threats, including botulinum toxin, tularemia, anthrax, and plague, could be targeted with passive immunization. Currently, most research and studies on using passive immunization for these threats are limited to animal models, and further experimental stages are required to establish their effectiveness. Efforts are ongoing to develop and evaluate passive immunization strategies to counteract potential bioterror events, ensuring rapid and effective responses to protect public health and mitigate the impact of such threats.

Advantages of Passive Immunity

Passive immunity offers several advantages over other forms of immunity, including the following:

• Quick Immune Response: Passive immunization provides a rapid immune response, typically within hours or days of administration. This is much faster compared to vaccines, which require weeks or months to produce protective immunity. The immediate protection offered by passive immunity is particularly valuable in emergency situations or when there is an immediate need for defense against specific pathogens.
• Overriding Deficient Immune Systems: Passive immunity can override a deficient or weakened immune system. This is especially beneficial for individuals who do not respond adequately to vaccine immunizations. Passive immunization can provide immediate protection to those who may have compromised immune systems or are unable to mount a robust immune response on their own.
• Immediate and Rapid Protection: Unlike active immunity, which takes time to develop, passive immunity through the injection of pre-formed antibodies offers immediate and rapid protection. This can be crucial in situations where there is an urgent need for defense, such as exposure to bioterrorism chemicals or outbreaks of infectious diseases.
• Effective in Challenging Conditions: Passive immunization is effective regardless of the recipient’s immune condition. This makes it a suitable treatment option in highly endemic regions where vaccine responses may be suboptimal or in specific patient groups, such as hospitalized individuals or those with malnutrition and immunodeficiency. It is also an option for individuals who are contraindicated for vaccination due to medical reasons.
• Additional Benefits of Nursing: In the case of natural passive immunity through breastfeeding, there are additional long-lasting health benefits for the infant. Breast milk provides antibodies, including IgA, that protect against infections and contribute to reducing the incidence of allergies and obesity in the child.

Disadvantages of Passive Immunity

• Cost and Complexity of Antibody Production: Antibodies used for passive immunity can be costly to produce, especially when they need to be harvested from the blood of numerous donors or obtained from immune animals. The production of antibodies in the laboratory can be challenging and expensive, requiring specialized techniques and facilities.
• Risk of Allergic Reactions: Antibodies derived from animals can potentially trigger serious allergic reactions in the recipient. When animal antibodies are administered, there is a risk of serum sickness and severe allergic responses due to the presence of animal proteins in the antibody preparation.
• Short-Lived Protection: The immunity conferred by passive immunization is temporary and does not lead to the formation of long-lasting memory immune cells. The effects of passive immunity diminish over time, and repeated dosing may be necessary to maintain protection. This is in contrast to active immunity induced by vaccines, which can provide long-term or lifelong protection.
• Challenges in Oral Administration: When antibodies are administered at the mucosal surface, such as through oral administration, they can be destroyed by gastric acid and proteolytic enzymes in the digestive system. This limits the effectiveness and practicality of oral administration for passive immunity.
• Potential for Viral Escape Mutants: The use of monoclonal antibodies (mAbs) in passive immunity can lead to the generation of viral escape mutants. These mutants lack the specific determinant targeted by the antibody, reducing the effectiveness of the treatment and potentially allowing the virus to evade immune detection.
• Temporary Protection: One of the limitations of passive immunization is that the protection it provides is short-lived. Since it involves the administration of pre-formed antibodies, the immune response does not stimulate the production of memory immune cells. As a result, the immunity conferred by passive immunization typically lasts for only a few weeks or months. This means that repeated doses may be required to maintain protection.
• Hypersensitivity Reactions: Passive immunization carries the risk of hypersensitivity reactions, especially when the administered antibodies are derived from a different species. These reactions can range from mild allergic responses to severe anaphylaxis. It is essential to consider the source and compatibility of the antibodies to minimize the risk of adverse reactions.
• Limited Applicability: Passive immunization using antibodies is not suitable for routine cases of diseases. It is primarily reserved for specific situations where immediate protection is necessary, such as in cases of exposure to a known pathogen or for individuals with compromised immune systems. In most cases, active immunization through vaccination is the preferred approach for long-term protection.
• Production Challenges: Antibodies used for passive immunization can be difficult and costly to produce. The production process often involves complex techniques, including the isolation and purification of specific antibodies. Additionally, large-scale production may be required to meet the demand for therapeutic antibodies, further adding to the cost and logistical challenges.
• Administration Complexity: Many antibody treatments used in passive immunization need to be administered through intravenous injection. This method requires trained healthcare professionals, specialized equipment, and a more time-consuming procedure compared to the administration of vaccines, which can be done through simpler methods like intramuscular or subcutaneous injections. Intravenous injections may also carry some risks and complications.

Examples of Passive Immunity

Skin as a Passive Immunity

• The skin is a vital component of passive immunity in the majority of mammals. The skin is an organ composed of numerous layers of elongated cells.
• These epidermal cells develop intercellular connections and create a nearly impermeable covering. In reality, it is extremely rare that a virus or bacteria could ever penetrate healthy, unbroken skin.
• The issue is that viruses, bacteria, and numerous poisons are tiny. It only takes a minuscule skin tear for millions of viruses and bacteria to penetrate.
• Active immunities must be created to battle the reproduction of viruses and bacteria and the spread of toxins in the event of a failure of passive immunity.
• While the skin has its drawbacks, it is important in shielding the body from the daily barrage of environmental threats it is exposed to.
• Without skin, you may absorb pollutants and disease straight from the air, water, and soil you contact.
• Simply by separating your internal cells from these threats, a barrier is created, offering passive immunity against a number of potentially dangerous foreign materials.
• However, if a substantial quantity of a toxin penetrates your skin, you could be in danger. Passive immunity is designed to prevent a disease or toxin from entering the body, whereas active immunity can create resistance to a disease after an initial infection. How can you survive if a high amount of toxin is able to penetrate your passive immunity?

Antivenom as a Passive Immunity

• If bitten by a rattlesnake, there is a possibility that you will be injected with the snake’s venom.
• The venom of a rattlesnake is hemotoxic, which means it kills your tissues and prevents your blood from clotting, leading you to bleed to death.
• Given sufficient exposure to little amounts of rattlesnake venom, your body would develop the ability to generate antibodies, allowing you to survive small doses of the venom. In a rattlesnake bite, however, enormous quantities of venom are pumped into the wound.
• Anti-venom administration would be your best chance of life in this situation. These serums include a high concentration of venom antibodies or proteins that attach to the venom and remove it from the bloodstream and tissues.
• Thus, the enormous amount of venom supplied to your system might be neutralised by a single shot or multiple ones.
• Unfortunately, the production of antivenoms is prohibitively expensive due to the fact that the antibodies are often produced in living animals and collected for use in humans.

Passive Immunity in Bacteria

• It has been demonstrated that certain bacteria can incorporate foreign DNA into their own systems.
• In doing so, they frequently obtain an advantage over other bacteria, allowing them to proliferate more.
• Antibiotics pose a danger to germs. Antibiotics function in many ways to destroy bacterial DNA or starve bacteria of nourishment.
• If a single microbe can generate a mutation that renders it resistant to an antibiotic, it will be able to multiply rapidly.
• As these bacteria die, they leave behind fragments of the DNA that enabled them to survive. Sometimes, other bacteria are able to incorporate these DNA fragments into their own DNA, giving them the ability to resist the antibiotic.
• Thus, they are provided with a new passive immunity to the medicine, similar to how infants develop immunity to sickness.

FAQ

References

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