Passive Immunity

Passive immunity occurs when a person receives antibodies from another source, rather than producing them through their own immune system. This type of immunity provides immediate protection against specific infections but is temporary, typically lasting only a few weeks to months. Passive immunity is often used in cases where there is an immediate risk of disease and insufficient time for the body to develop its own immune response, such as with newborns receiving maternal antibodies or people receiving antivenom after a snakebite.

What is Passive Immunity?

Passive immunity occurs when an individual is given antibodies from another source, rather than generating them internally through their own immune system. This form of immunity provides immediate protection against specific diseases but is temporary, lasting only a few weeks or months.

How Passive Immunity Works

Passive immunity can be acquired in several ways

• Natural Acquisition: Newborns receive passive immunity naturally when antibodies are transferred from the mother to the fetus through the placenta. This maternal transfer of antibodies provides the infant with immediate disease protection after birth.
• Artificial Acquisition: Individuals may also receive passive immunity through the administration of antibody-containing blood products, such as immune globulin. These are often used in medical settings when immediate protection against a disease is critical.

Function of Passive Immunity

Passive immunity is when a person gets temporary protection from diseases by receiving antibodies from another source, rather than making them through their own immune system. This kind of immunity is especially important in protecting against diseases in situations where someone’s immune system isn’t strong or fully developed. Here are the main functions and characteristics of passive immunity:

Immediate Protection

Passive immunity offers instant protection against diseases. Unlike active immunity, which takes time to develop after being exposed to a disease, passive immunity starts working right away. This is because the antibodies are already prepared and active when they enter the body.

Short-term Effectiveness

Although passive immunity acts immediately, it doesn’t last long. The borrowed antibodies are slowly broken down and removed from the body, usually in a few weeks to a few months. How long they last can vary based on where the antibodies came from.

Sources of Passive Immunity

• Natural Sources: The most common way to get passive immunity naturally is when a mother passes antibodies to her baby either through the placenta before birth, or through breast milk after birth. These antibodies are key in protecting newborns from infections in their first few months.
• Artificial Sources: People can also get passive immunity through medical treatments that include antibodies, like immune globulin. These treatments help prevent or fight diseases in people who have been exposed to infections or who have weak immune systems.

Types of Passive Immunity

Natural Passive Immunity

Natural passive immunity gives immediate protection to infants against infections, which is vital in their early development. This immunity mainly comes from maternal antibodies. In the third trimester, antibodies and cells that fight pathogens move from the placenta to the fetus, providing crucial defenses before birth. After birth, infants get colostrum during the first nursing sessions, which is rich in antibodies and boosts their immune defense. Although breast milk has fewer protective components than colostrum, it still significantly helps the infant’s immunity. However, this protection is temporary, with maternal antibody levels dropping by about six months of age.

Artificial Passive Immunity

Artificial passive immunity involves giving antibodies to a person who hasn’t been exposed to a pathogen. These antibodies can come from the blood of people who have recovered from a disease or from vaccinated animals like horses, which were among the first sources for making antibody treatments. Today, this method is used to treat various infections, especially when an immediate immune response is needed in people with weak immunity.

The History of Passive Immunization

Passive immunization started in the late 19th century with the work of Shibasaburo Kitasato and Emil von Behring. They first protected guinea pigs against diphtheria using heated blood from animals that had recovered from the disease. This was the first successful use of antibodies to treat a disease. Their work led to the creation of the diphtheria antitoxin, which soon became a standard treatment for human diphtheria. This method also laid the groundwork for using antibody-rich blood products to fight diseases like tetanus, smallpox, and bubonic plague. Research in the 20th century expanded these methods to prevent diseases like measles and infectious hepatitis, greatly impacting modern medicine.

Passive Immunization Today

Now, doctors use passive immunization as a treatment and as a way to prevent diseases in high-risk patients or those recently exposed to germs. They use antibodies to fight diseases like diphtheria, cytomegalovirus, hepatitis A, hepatitis B, rabies, and chickenpox. These treatments are crucial for people with weak immune systems or those who need immediate protection, providing essential defense until the body can develop its own immunity through natural exposure or vaccination.

Examples of Passive Immunity

Here are some primary examples that illustrate how passive immunity operates in various scenarios:

1. Maternal Antibodies

• During Pregnancy: A pregnant woman transfers antibodies to her fetus through the placenta, providing the newborn with immediate protection against infections during the vulnerable early months.
• Through Breastfeeding: A mother passes antibodies to her baby via breast milk, which helps protect the infant as their immune system matures.

2. Immune Globulins

• Post-exposure Prophylaxis: Healthcare providers administer immune globulin injections to individuals exposed to viruses like hepatitis A or measles. This administration can prevent the diseases from developing in those without vaccinations or natural immunity.
• Chronic Immune Conditions: Patients with weakened immune systems or insufficient antibody production (e.g., due to certain types of immunodeficiency) often receive regular immune globulin doses to help prevent infections.

3. Antitoxins and Antivenoms

• Antitoxins: Healthcare professionals use antitoxins to counteract toxins from bacterial infections such as tetanus or diphtheria. They collect these antitoxins from animals or humans immunized against the toxin.
• Antivenoms: To neutralize venom from snake or spider bites, manufacturers produce antivenoms by immunizing horses or other animals with small amounts of specific venom and then harvesting the antibodies.

4. Monoclonal Antibodies

• Disease Treatment: Researchers engineer monoclonal antibodies in laboratories to target specific antigens, like those on cancer cells or pathogens. Doctors administer these antibodies to patients to help combat diseases such as certain cancers, COVID-19, or autoimmune disorders.

Advantages of Passive Immunity

• Immediate Response: Passive immunity works rapidly, typically producing an immune response within hours to days. This speed is crucial in emergency situations or when immediate protection is needed.
• Suitability for Immune-Compromised Individuals: It is particularly beneficial for individuals with weakened immune systems who cannot respond adequately to traditional vaccinations. This method can provide them with necessary antibodies they are otherwise unable to produce.

Disadvantages of Passive Immunity

• Production Challenges and Costs: Producing antibodies can be expensive and technically challenging. Many antibodies for infectious diseases need to be collected from the plasma of numerous human donors or from immunized animals. This process can be not only costly but also limited by the availability of donors.
• Risk of Allergic Reactions: Antibodies derived from animal sources can trigger serious allergic reactions in recipients, posing a significant health risk.
• Administration Complications: Unlike vaccines, which are often simple injections, many antibody treatments require intravenous administration. This method is more time-consuming, requires medical expertise, and can be more invasive.
• Temporary Immunity: The immunity conferred by passive immunity is short-lived. It does not induce long-term memory in the immune system, meaning it does not provide lasting protection against future exposures to the disease.

FAQs

What is Passive Immunotherapy?

Passive immunotherapy involves administering pre-made antibodies to enhance the body’s defense against specific diseases.

What is Active Immunity Examples?

Examples of active immunity include immunity developed from vaccinations or recovering from diseases like measles.

What is the Most Important Source of Passive Immunity in Pregnancy?

The most important source of passive immunity in pregnancy is the transfer of maternal antibodies to the fetus via the placenta.

What is Passive Immunity and Why is It Important?

Passive immunity provides immediate but temporary protection against infections by introducing external antibodies, crucial for immediate defense in vulnerable populations.