11.2 Antibodies and Vaccination
- Syllabus
- 9700–2028–2029
- Topic
- 11.2
- Level
- AS
Learning objectives
11.2.1Antibody molecular structure and functions• Antibody molecular structure and functions11.2.2Hybridoma method• Hybridoma method for monoclonal antibody production11.2.3Monoclonal antibody uses• Monoclonal antibodies in disease diagnosis and treatment11.2.4Types of immunity• Active vs passive immunity; natural vs artificial immunity11.2.5Vaccines• Vaccines: antigens stimulate immune responses for long-term immunity11.2.6Vaccination programmes• Vaccination programmes in controlling infectious disease spread
Antibody molecular features connect recognition to immune action
An antibody is a Y-shaped globular glycoprotein secreted by plasma cells. It contains two identical heavy polypeptide chains and two identical light chains held together by disulfide bonds.
| Molecular feature | Functional consequence |
|---|---|
| Variable regions at both tips | Form two identical antigen-binding sites whose shapes are complementary to one antigen epitope, giving specificity |
| Two binding sites | Bind two antigens or particles and can cross-link them into agglutinated groups that phagocytes remove more easily |
| Hinge region | Gives flexibility so both sites can bind epitopes at different orientations or separations |
| Constant region | Binds receptors on immune cells or complement components after antigen binding, promoting opsonisation and other effector responses |
| Disulfide bonds | Stabilise the four-chain Y-shaped molecule while preserving its binding arrangement |
Specific binding forms an antigen–antibody complex. Depending on the target, this can neutralise a toxin or virus, agglutinate cells or pathogens, mark a target for phagocytosis, or activate complement-associated damage.
Variable regions determine antigen specificity; constant regions help recruit later immune effects. Antibodies bind and mark or block targets but do not digest pathogens themselves.
Hybridoma production links antibody specificity to continuous cell division
A hybridoma is a fused cell line used to produce large quantities of one monoclonal antibody. It combines an antibody-producing B-cell lineage with a tumour-cell lineage that can continue dividing.
- Stimulate antibody production: Inject an animal with the relevant antigen so specific antibody-producing B lymphocytes, including plasma-cell descendants, are generated.
- Isolate antibody-producing cells: Remove the stimulated B-cell population from the animal.
- Fuse cell types: Fuse the B cells with tumour cells to form hybridoma cells. The fused cell combines antibody specificity from the B-cell lineage with the capacity for continued mitotic division from the tumour-cell lineage.
- Select and screen: Grow the fusion products in selective medium, then test the surviving hybrid cells for production of the desired antibody. Selection alone does not prove the antibody has the required specificity.
- Clone and expand: Isolate a hybridoma producing the desired antibody, clone that line, and culture it to produce large quantities of identical monoclonal antibody.
The sequence matters: antigen stimulation supplies specificity; fusion supplies a hybrid cell with both antibody production and sustained division; selection removes unsuitable fusion products; screening identifies the required specificity; cloning preserves one antibody-producing cell line for expansion.
This card explains how monoclonal antibodies are made. Their diagnostic and therapeutic uses belong to the next objective; the broader primary immune-response sequence belongs to the neighbouring immune-response card.
Monoclonal specificity enables targeted diagnosis and treatment
All antibodies in one monoclonal preparation have the same binding site, so they bind the same target antigen with high specificity.
| Use | Principle | Meaning of the result |
|---|---|---|
| Diagnosis | Attach a detectable label to a monoclonal antibody; if its target antigen is present in a sample or tissue, binding concentrates the label at that target | A measured signal indicates that the target antigen was bound; controls and a threshold are needed to interpret it |
| Treatment | Choose an antibody that binds an antigen or receptor concentrated on a disease-related cell; binding can block a signal, recruit immune destruction, or deliver an attached drug or radioactive substance to the target | Targeting increases action at antigen-bearing cells, but non-target binding and antigen variation can limit selectivity |
The shared logic is target antigen present → complementary monoclonal antibody binds. Diagnosis converts binding into a detectable signal; treatment converts binding into a local biological or therapeutic effect.
A diagnostic signal shows target binding, not automatically disease severity or complete cause. 'Targeted' treatment is selective rather than perfectly exclusive, so specificity and side effects must still be evaluated.
Active and passive immunity differ in how protection is acquired
Active immunity is protection made by the person’s own immune response after an antigen is encountered. Passive immunity is protection supplied by antibodies made elsewhere, so the recipient’s immune system is not the source of those antibodies.
- Active — natural: Exposure to a pathogen provides the antigen; the person produces antibodies and memory cells. Protection takes time to build, but memory can support a faster, stronger response to the same antigen later.
- Active — artificial: A vaccination provides antigenic stimulation without requiring the person to first develop the disease; the person produces antibodies and memory cells. The specific vaccination process is covered in the following objectives.
- Passive — natural: Ready-made antibodies pass from another person, such as across the placenta or in colostrum. Protection is available without the recipient making the antibodies, but no memory cells are formed.
- Passive — artificial: Ready-made antibodies are injected or infused, for example an antitoxin when rapid protection is needed. Antibodies are available promptly, but the recipient does not form memory cells and may need another antibody supply after reinfection.
The key distinction is who makes the antibodies. Own production in active immunity explains the slower primary response and the presence of memory cells; supplied antibodies in passive immunity explain the immediate protection but the absence of a memory-based secondary response.
Active does not mean immediate, and passive does not create immunological memory. Natural versus artificial describes how the immunity is acquired; active versus passive describes whether the recipient makes the antibodies. This card does not give the detailed steps of vaccination or disease-control programmes.
Vaccination creates active artificial immunity through antigenic memory
A vaccine introduces antigenic material deliberately to produce active artificial immunity. The material is chosen to stimulate a specific immune response without being intended to cause the disease.
- Antigenic stimulation: Vaccine material presents antigens to the immune system. It may contain weakened whole pathogens, inactivated whole pathogens, or selected pathogen components such as proteins, sugars or toxoids.
- Primary response: The antigens trigger a specific immune response, including plasma cells releasing antibodies against the vaccine antigen.
- Memory formation: The response also forms memory cells. These cells preserve the antigen-specific information after the initial response has declined.
- Later exposure: If the person encounters the same antigen again, memory cells help produce a faster and stronger secondary response, so antibodies can rise more rapidly and help control the pathogen before serious disease develops.
Vaccine antigen → primary antibody response → memory-cell formation → quicker, larger secondary response on re-exposure. This is active artificial immunity because the vaccinated person’s own immune system makes the response; the vaccine is not a direct infusion of ready-made antibodies.
A vaccine is not the same as passive antibody treatment, and protection is not an instant guarantee against every exposure. This card explains the immune principle and the safety distinction between vaccine material and disease-causing infection; population vaccination programmes belong to the next objective.
Vaccination programmes reduce transmission as well as individual risk
A vaccination programme protects a population when a sufficiently large proportion of people become immune. This population-level protection is herd immunity: fewer susceptible hosts make it harder for a pathogen to spread.
- Coverage: A coordinated immunisation schedule makes vaccination available across the relevant population. Coverage is not just an individual decision: delivery, access, resources and acceptance affect how many people become immune.
- Fewer susceptible hosts: Each immune person is less likely to contract and pass on the disease, so the pathogen encounters fewer suitable transmission opportunities.
- Transmission falls: When enough people are immune, chains of transmission become harder to maintain and disease levels stay low within the population.
- Indirect protection: People who are not immunised can be less likely to encounter the pathogen because spread is reduced around them. This matters especially for people who cannot rely on vaccination or have higher risk from infection.
- Limits: Herd immunity is not an absolute barrier. If coverage is too low, uneven, inaccessible or poorly maintained, enough susceptible people remain for transmission to continue; protection also depends on the vaccine and pathogen combination rather than on a universal guarantee.
This card is about population coverage and transmission, not the individual vaccine mechanism in 4637 or the active/passive classification in 4636. Herd immunity protects through reduced spread; it does not mean every person is directly vaccinated or that infection is impossible.