11.3 Types of Immunity
Immunity protects the human body from infectious diseases through specific immune responses. It is classified into active immunity and passive immunity, depending on whether the body produces its own antibodies or receives them from an external source. Both active and passive immunity can be acquired naturally or artificially.
Learning Objectives
- State the meaning of active immunity and passive immunity.
- Classify immunity into natural active, artificial active, natural passive, and artificial passive immunity.
- Explain the characteristics, mechanisms, and examples of natural active immunity and artificial active immunity.
- Explain the characteristics, mechanisms, and examples of natural passive immunity and artificial passive immunity.
- Compare and contrast artificial active immunity and artificial passive immunity.
- Interpret graphs showing changes in antibody levels following vaccination and antiserum injections.
Comparison of Artificial Active and Artificial Passive Immunity
Vaccination and antiserum injection both protect the body, but they differ in injected substance, purpose, onset of protection and antibody response over time.
Artificial Active Immunity
Acquired through a vaccine injection. The vaccine contains weakened, dead or non-virulent pathogens that stimulate lymphocytes to produce antibodies.
- First injection produces a low antibody concentration below the level of immunity.
- A booster dose raises antibody production above the level of immunity.
- Protection lasts for a long period of time.
Artificial Passive Immunity
Acquired through an antiserum injection. The antiserum contains ready-made specific antibodies from an external source.
- Provides immediate protection against toxins or pathogens.
- Protection is temporary because antibodies are gradually broken down.
- No memory cells are formed.
Short Explanation
Classification of Immunity
Active immunity occurs when lymphocytes produce their own antibodies in response to stimulation by antigens, providing long-lasting protection. Passive immunity occurs when the body receives ready-made antibodies from an external source without producing its own antibodies, providing immediate but temporary, short-term protection.
Natural Active Immunity
Acquired after an individual recovers from an infection. When infected by pathogens, lymphocytes produce antibodies in response to the antigens. Upon recovery, the individual gains permanent immunity against the disease.
Lymphocytes that store memory of the pathogen, called memory cells, remain in the body. If attacked again by the same pathogen, memory cells rapidly produce antibodies to react immediately against the antigens.
Examples: Recovering from chickenpox or influenza.
Artificial Active Immunity
Acquired when an individual is given a vaccine injection, also called immunisation. A vaccine is a suspension of pathogens that are weakened, dead, or non-virulent.
The injected vaccine stimulates lymphocytes to produce antibodies against the pathogens. The first vaccine injection produces a low concentration of antibodies, which is insufficient to reach the level of immunity required to protect against the disease.
A booster dose must be administered to increase antibody production above the level of immunity.
Examples: Salk vaccine for poliomyelitis, BCG vaccine for tuberculosis, HPV vaccine for cervical cancer.
Natural Passive Immunity
Acquired naturally from mother to child. Antibodies from the mother diffuse across the placenta into the foetal bloodstream during pregnancy.
After birth, antibodies protect the baby during the first few months through breast milk or colostrum during breastfeeding.
Artificial Passive Immunity
Acquired through an injection of antiserum, which is serum containing specific antibodies.
It provides immediate protection against toxins or pathogens, but the protection is temporary and lasts only for a short period because the antibodies are gradually broken down.
Examples: Antitetanus, anti-rabies, and antiserum for poisonous snake bites.
Preparation of Antiserum — Antitetanus
- Tetanus toxoid suspension is injected into a horse.
- The horse produces antibodies against tetanus toxoid.
- Antitetanus antibodies from horse serum are concentrated and purified.
- Antiserum is injected into an individual with a high risk of tetanus to provide immediate protection.
Comparison between Artificial Active Immunity and Artificial Passive Immunity
| Aspect | Artificial Active Immunity | Artificial Passive Immunity |
|---|---|---|
| Acquired through | Vaccine injection | Antiserum injection |
| Injected substance | Suspension of weakened, dead, or non-virulent pathogens | Serum containing specific antibodies |
| Purpose | Prevention | Treatment or when immediate protection is required |
| Effect | Does not give immediate protection (slow response) | Gives immediate protection |
| Immunity period | Lasts for a long period of time | Temporary and does not persist |
| When injection is given | Administered before being infected | Given in advance if there is a high risk of infection or immediately after infection |
| Source of antibody | Produced by the individual's own lymphocytes | Obtained directly from antiserum |
| Need for a second injection | Booster dose must be given to increase antibody level above the level of immunity | Only given when the antibody level in the blood drops below the level of immunity and the patient is still infected |
Similarities: Both protect the body from infectious diseases, and both involve interactions between antibodies and antigens.
Antibody Concentration Graphs
The level of immunity is the concentration of antibodies in the blood that is sufficient to fight the disease.
Vaccination graph: The first injection causes the antibody level to increase slowly but remain below the level of immunity, then decline. The second injection, or booster dose, causes a rapid and sharp increase in antibody level, rising well above the level of immunity and persisting for a long duration.
Antiserum graph: The first injection causes the antibody level to immediately spike above the level of immunity, but it declines rapidly below the level of immunity as antibodies are eliminated. A second injection is only administered if the individual is still infected, temporarily spiking antibody concentration again.
Try to Answer First
Answer in your mind, then press “Check Answer”.
Why does a person bitten by a venomous snake require an antiserum injection rather than a vaccine?
What is the function of a booster dose in artificial active immunity?
State how a newborn baby gains natural passive immunity.
Common Mistakes
- Confusing a vaccine with an antiserum: students often incorrectly state that vaccines contain ready-made antibodies or that antiserums contain weakened pathogens.
- Believing passive immunity creates long-term immunity: students forget that passive immunity does not involve memory cell production; hence, it provides only short-term, temporary protection.
- Misinterpreting the purpose of the first vaccine dose: assuming one dose is always enough to achieve protection, overlooking that the antibody level from the first dose usually remains below the level of immunity.
Concept Misunderstandings
Antiserum stimulates the body's immune system to manufacture its own antibodies.
Antiserum supplies ready-made antibodies from an external source, such as horse serum. It does not trigger the recipient's lymphocytes to produce antibodies or form memory cells.
Active immunity provides immediate defence against a pathogen upon first exposure.
Active immunity takes time to develop because the body's lymphocytes must first identify the antigen, divide, and synthesise specific antibodies.
Summary
- Immunity is divided into active immunity, where antibodies are made by the body's lymphocytes, and passive immunity, where antibodies are received from an external source.
- Natural active immunity is acquired by recovering from an infection and creates memory cells for long-lasting defence.
- Artificial active immunity is achieved via vaccines containing weakened, dead, or non-virulent pathogens; booster doses are required to raise antibodies above the level of immunity.
- Natural passive immunity involves transfer of maternal antibodies via the placenta or breast milk/colostrum.
- Artificial passive immunity involves injecting antiserum containing pre-formed antibodies for immediate, short-term treatment of acute risks like snake bites or tetanus.
Short Activity
Objective: classify types of immunity and compare vaccination with antiserum.
A. Objective Quiz
Which of the following correctly pairs the type of immunity with its method of acquisition?
Why must a booster dose be administered during an immunisation programme?
B. Fill in the Blanks
A suspension of pathogens that are weakened, dead, or non-virulent injected to stimulate antibody production is called a .
The concentration of antibodies in the blood that is sufficient to fight a disease is referred to as the level of .
C. Matching / Drag and Drop
Match each type of immunity to its correct example or description. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Type of Immunity to Its Example or Description
Write the correct type of immunity next to each description.
| Example or Description | Type of Immunity |
|---|---|
| 1. Gained when an individual recovers from chickenpox or influenza | |
| 2. Induced by injecting the Salk vaccine or BCG vaccine | |
| 3. Acquired by a baby through colostrum or across the placenta | |
| 4. Provided by injecting antiserum against snake venom or tetanus |
Answer choices: Natural active immunity • Artificial active immunity • Natural passive immunity • Artificial passive immunity
