Passive Immunity- Definition, Characteristics, Types, Examples

Passive immunity is a type of immunity that does not involve the production of antibodies by the immune system of the individual. Instead, it relies on the transfer of antibodies from another source, such as another person or an animal, into the body of the recipient. These antibodies can bind to and neutralize the antigens of foreign invaders, such as bacteria, viruses, toxins, or parasites, and protect the individual from infection or disease.

Passive immunity is the type of immunity that is developed by antibodies produced outside and introduced into the body. Unlike active immunity, which requires the body to encounter an antigen and produce its own antibodies, passive immunity does not involve the body`s own immune response. Therefore, passive immunity has some distinctive characteristics:

• Immediate response: Passive immunity provides immediate protection against an infectious agent or its toxin, since the antibodies are already present and do not need to be synthesized by the body. This is especially useful in emergency situations, such as exposure to rabies or tetanus, where waiting for the body to mount an active immune response could be fatal.
• Short lifespan: Passive immunity is not as long-lasting as active immunity, since the antibodies are gradually degraded and eliminated from the body. The duration of passive immunity depends on the type and amount of antibodies administered, but it usually lasts a few days, weeks, or months. For example, maternal antibodies transferred to the fetus during pregnancy can last up to 6 months after birth, while antiserum injections can last from a few days to a few weeks.
• No memory: Passive immunity does not induce the formation of memory cells, which are responsible for the long-term protection and faster response in active immunity. This means that passive immunity does not confer lasting immunity or immunological memory to the recipient. Therefore, passive immunity needs to be repeated or supplemented with active immunization for sustained protection.

Passive immunity can be classified into two types: natural and artificial. Natural passive immunity occurs when antibodies are transferred from one person to another without any intervention, such as during pregnancy or breastfeeding. Artificial passive immunity occurs when antibodies are administered to a person by injection or infusion, such as in the case of antiserum or serum therapy. Both types of passive immunity have advantages and disadvantages, depending on the situation and the disease.

Natural passive immunity occurs when antibodies are transferred from one person to another without any deliberate intervention. The most common example of natural passive immunity is the maternal-fetal transfer of antibodies during pregnancy and breastfeeding.

During pregnancy, IgG antibodies from the mother cross the placenta and enter the fetal bloodstream. These antibodies provide protection to the fetus and the newborn against various infections, such as tetanus, measles, rubella, and chickenpox. The level of maternal antibodies in the newborn depends on the mother`s immune status and the duration of pregnancy. The maternal antibodies gradually decline in the first few months of life, leaving the infant vulnerable to infections unless they receive active immunization.

Another example of natural passive immunity is the maternal-infant transfer of antibodies through breast milk, especially colostrum. Colostrum is the first milk produced by the mother after giving birth, which is rich in IgA antibodies. These antibodies coat the mucosal surfaces of the infant`s gastrointestinal and respiratory tracts, preventing the attachment and invasion of pathogens. Breastfeeding also provides other immune factors, such as lactoferrin, lysozyme, and cytokines, that enhance the infant`s immune system. The protection conferred by breast milk lasts as long as breastfeeding continues, but it does not prevent systemic infections.

Natural passive immunity is important for the survival and health of newborns and infants, who have an immature immune system and cannot produce enough antibodies on their own. However, natural passive immunity is not always sufficient or reliable, and it may interfere with the response to some vaccines. Therefore, it is recommended that infants receive timely and complete immunization according to the national schedule.

Artificial passive immunity is a type of immunity that is induced by introducing antibodies from an external source into the body. These antibodies are usually produced in a laboratory or obtained from the blood of animals or humans that have been exposed to a specific antigen. Artificial passive immunity is often administered by injection, either intravenously or intramuscularly.

Artificial passive immunity is used in situations where there is a high risk of infection or when the body`s own immune system is not able to produce enough antibodies. For example, artificial passive immunity can be used to treat or prevent:

• Rabies: a viral infection that affects the nervous system and can be fatal if not treated promptly. Rabies immunoglobulin (RIG) is a preparation of human or animal antibodies that can neutralize the rabies virus. RIG is given as soon as possible after exposure to a rabid animal, along with a series of rabies vaccines.
• Tetanus: a bacterial infection that causes severe muscle spasms and can lead to death by suffocation. Tetanus immunoglobulin (TIG) is a preparation of human antibodies that can bind to the tetanus toxin and prevent it from affecting the nerves. TIG is given as soon as possible after exposure to a contaminated wound, along with a tetanus vaccine.
• Hepatitis A and B: viral infections that affect the liver and can cause inflammation, jaundice, and liver failure. Hepatitis A immunoglobulin (HAIG) and hepatitis B immunoglobulin (HBIG) are preparations of human antibodies that can protect against hepatitis A and B viruses, respectively. HAIG and HBIG are given as soon as possible after exposure to a source of infection, such as contaminated food or water (for hepatitis A) or blood or body fluids (for hepatitis B), along with hepatitis vaccines.
• Snake bites: venomous snake bites can cause severe tissue damage, bleeding, shock, and death. Antivenom is a preparation of animal antibodies that can neutralize the venom of different types of snakes. Antivenom is given as soon as possible after a snake bite, along with supportive care.

Artificial passive immunity has some advantages over active immunity, such as providing immediate protection and being effective even in immunocompromised individuals. However, it also has some disadvantages, such as being expensive to produce, requiring repeated doses to maintain protection, and carrying the risk of allergic reactions or serum sickness. Therefore, artificial passive immunity is usually reserved for emergency situations or when active immunity is not feasible or available.

Antiserum is a blood serum that contains antibodies against a specific antigen. Serum therapy is the use of antiserum to treat or prevent diseases caused by pathogens or toxins.

Serum therapy was first developed in the late 19th century by Emil von Behring and Shibasaburo Kitasato, who discovered that injecting serum from animals immunized with diphtheria or tetanus toxins could protect or cure humans from these diseases. They were awarded the Nobel Prize in Physiology or Medicine in 1901 for this discovery.

Serum therapy was also used to treat other infectious diseases, such as plague, typhoid fever, meningitis, and pneumonia. However, serum therapy had some limitations and drawbacks, such as:

• The availability and quality of antiserum depended on the source animals and their immunization status.
• The antiserum could contain harmful contaminants or pathogens from the animals or the donors.
• The antiserum could cause adverse reactions in the recipients, such as anaphylaxis, serum sickness, or hemolysis.
• The antiserum could induce passive immunity only for a short period of time and could not stimulate active immunity or memory cells in the recipients.
• The pathogens could develop resistance or escape mechanisms against the antiserum.

With the development of vaccines and antibiotics in the 20th century, serum therapy became less widely used. However, it is still used in some situations where vaccines are not available or effective, such as:

• Rabies: Post-exposure prophylaxis with human rabies immunoglobulin (HRIG) and rabies vaccine can prevent rabies infection after exposure to a rabid animal.
• Botulism: Antitoxin derived from horses can neutralize botulinum toxin and reduce the severity and duration of symptoms.
• Snakebite: Antivenom produced from horses or sheep can bind and inactivate snake venom and prevent or reverse its effects.
• Tetanus: Tetanus immunoglobulin (TIG) can provide immediate protection against tetanus toxin in unvaccinated or incompletely vaccinated individuals who have a tetanus-prone wound.

Serum therapy is also being explored as a potential treatment for emerging or re-emerging infectious diseases, such as Ebola, Zika, COVID-19, and others. However, there are still challenges and limitations to overcome, such as:

• The safety and efficacy of antiserum need to be tested and validated in clinical trials.
• The production and distribution of antiserum need to be scaled up and standardized to meet the demand and quality standards.
• The ethical and regulatory issues related to the use of human or animal sources of antiserum need to be addressed.
• The cost-effectiveness and accessibility of antiserum need to be improved for low-resource settings.

Passive immunity has many applications in medicine and public health, especially for the treatment and prevention of various diseases. Some examples of passive immunity today are:

• Convalescent plasma: This is the blood plasma of people who have recovered from an infection, such as COVID-19. It contains antibodies that can help fight the same infection in other patients. Convalescent plasma can be transfused to patients who are severely ill or at high risk of complications. It can also be used as a preventive measure for people who have been exposed to the infection but have not developed symptoms yet.
• Antiserum and serum therapy: This is the administration of antibodies that are produced in animals or humans against a specific pathogen or toxin. Antiserum can be used to treat or prevent diseases such as botulism, diphtheria, hepatitis A and B, measles, rabies, tetanus, and snake venom poisoning. Serum therapy can also be used to treat non-infectious diseases such as hemophilia, immune thrombocytopenia, and Kawasaki disease.
• Monoclonal antibodies: These are antibodies that are made in the laboratory and target a specific antigen on a pathogen or a cell. Monoclonal antibodies can be used to treat or prevent infectious diseases such as respiratory syncytial virus (RSV), cytomegalovirus (CMV), anthrax, and plague. They can also be used to treat non-infectious diseases such as cancer, multiple sclerosis, rheumatoid arthritis, Crohn`s disease, and cardiovascular disease.

Passive immunity can provide immediate and effective protection against various threats, especially for people who have weak or compromised immune systems. However, passive immunity also has some limitations and challenges, such as high cost, limited availability, short duration, and potential side effects. Therefore, passive immunity should be used in combination with other strategies, such as vaccination and hygiene measures, to achieve optimal health outcomes.

Passive immunization has been used for decades to treat and prevent various infectious diseases, but it also has some limitations and challenges. However, with the advancement of biotechnology and immunology, new methods and applications of passive immunization are emerging that could overcome some of the drawbacks and expand its potential benefits. Here are two examples of the future directions of passive immunization:

Monoclonal antibodies

Monoclonal antibodies (MAbs) are antibodies that are produced by a single type of immune cell and that recognize a specific antigen. Unlike conventional antibodies that are derived from the blood of animals or humans and that contain a mixture of different antibodies, MAbs are pure and specific. MAbs can be produced in the laboratory by using various techniques, such as hybridoma technology, recombinant DNA technology, or phage display technology.

MAbs have many advantages over conventional antibodies for passive immunization. They can be designed to target a specific part of a pathogen or a toxin, thus enhancing their efficacy and reducing their side effects. They can also be modified to improve their stability, solubility, or half-life in the body. Moreover, they can be humanized or fully human to reduce the risk of allergic reactions or immune rejection.

MAbs have been successfully used for the prevention and treatment of various diseases, such as respiratory syncytial virus (RSV), hepatitis B virus (HBV), rabies virus, cytomegalovirus (CMV), anthrax, botulism, and cancer. However, there are still some challenges and limitations for the development and use of MAbs for passive immunization. For example, MAbs are expensive and difficult to produce in large quantities. They also require intravenous administration, which may not be feasible in some settings. Furthermore, some pathogens may mutate or evade the recognition by MAbs, thus reducing their effectiveness.

Bioterror threats

Bioterrorism is the intentional release of biological agents that can cause disease or death in humans, animals, or plants. Bioterrorism poses a serious threat to public health and national security, as it can cause widespread panic, morbidity, mortality, and social disruption. Some examples of potential bioterror agents include anthrax, plague, tularemia, botulism toxin, ricin toxin, smallpox virus, and Ebola virus.

Passive immunization can play a vital role in the response to a bioterror attack, as it can provide immediate protection to the exposed individuals or populations. Unlike vaccines that require time to induce an immune response and may need multiple doses or boosters, passive immunization can confer instant immunity by transferring preformed antibodies to the recipient. Passive immunization can also overcome the limitations of the immune system in some individuals who may not respond well to vaccines.

However, passive immunization for bioterror threats also faces some challenges and limitations. For example, there may not be enough supply or availability of antibodies for mass prophylaxis or treatment in case of a large-scale attack. There may also be ethical or legal issues regarding the distribution and allocation of antibodies among different groups or regions. Moreover, some bioterror agents may be resistant or unfamiliar to the existing antibodies, thus requiring the development of new antibodies.

Passive immunization has some advantages over active immunization, especially in situations where immediate protection is needed or when the immune system is compromised. Some of the benefits of passive immunization are:

• Quick response: Passive immunization acts faster than active immunization, producing an immune response within hours or days of the administration. This is because passive immunization delivers ready-made antibodies to the body, whereas active immunization requires the body to produce its own antibodies, which takes time. Passive immunization can be useful in emergencies, such as exposure to a toxin or a pathogen, or in outbreaks of infectious diseases.
• Can override deficient immune system: Passive immunization can also help people who have a weak or impaired immune system, such as newborns, elderly, or immunocompromised individuals. These people may not respond well to active immunization, either because they cannot produce enough antibodies or because they have a higher risk of adverse reactions to vaccines. Passive immunization can provide them with temporary protection against certain diseases, without triggering their immune system. Passive immunization can also be used as an adjunct to active immunization, to boost the immune response and enhance the efficacy of vaccines.

Passive immunization has some drawbacks that limit its use and effectiveness. Some of the disadvantages of passive immunization are:

• Costly to produce: Antibodies are expensive to produce and require a large amount of blood from donors or animals. New technologies such as monoclonal antibodies and recombinant systems can help reduce the cost and increase the availability of antibodies, but they are still not widely accessible or affordable for many diseases and regions.
• Can cause allergic reactions: Antibodies from animals or other humans can trigger an immune response in the recipient, leading to allergic reactions such as serum sickness, anaphylaxis, or hemolytic anemia. These reactions can be mild or severe, depending on the type and amount of antibodies, the route of administration, and the individual`s sensitivity. To prevent or reduce these reactions, antibodies are usually purified, screened, and tested before use. However, some risk of adverse effects remains.
• Short-lived: Antibodies have a limited lifespan in the body and are gradually degraded or eliminated. This means that passive immunity does not last long and requires repeated doses to maintain protection. Passive immunity also does not stimulate the production of memory cells, which are responsible for long-term immunity and protection against reinfection. Therefore, passive immunity cannot replace active immunity conferred by vaccines or natural infection.

We are Compiling this Section. Thanks for your understanding.