Cambridge A-Level Biology 9700 – Antibodies and \cdot accination
Antibodies and \cdot accination
Immunity can be classified in two independent ways:
by the source of the protective agents – active or passive immunity;
by the way the immune response is acquired – natural or artificial immunity.
Active vs Passive Immunity
Active immunity occurs when an individual's own immune system is stimulated to produce antibodies and memory cells.
Induced by exposure to the antigen (e.g., infection or vaccination).
Provides long‑term protection because memory B‑cells are formed.
Usually takes days to weeks to develop fully.
Passive immunity provides immediate protection by supplying ready‑made antibodies from another source.
Antibodies are transferred (e.g., maternal IgG across the placenta, or immunoglobulin serum).
No memory cells are generated, so protection is short‑lived (weeks to a few months).
Useful when rapid protection is required or when the host cannot mount an active response.
Natural vs Artificial Immunity
Natural immunity is acquired through exposure to the pathogen in the environment.
Can be active (infection leading to antibody production) or passive (maternal antibodies transferred to the newborn).
Occurs without medical intervention.
Artificial immunity is obtained through medical procedures.
Active artificial immunity: vaccination with a weakened, killed, or component of the pathogen.
Passive artificial immunity: administration of immune serum or monoclonal antibodies.
Allows control over timing, dosage, and safety of the immune stimulus.
Comparison Table
Type
Source of Antibodies
Memory Cells Formed?
Duration of Protection
Typical Example
Active – Natural
Self‑produced after natural infection
Yes
Years to lifelong
Recovery from measles infection
Active – Artificial
Self‑produced after vaccination
Yes
Years to lifelong (booster‑dependent)
MMR vaccine
Passive – Natural
Maternal IgG transferred via placenta or colostrum
No
Weeks to a few months
Newborn’s protection against tetanus
Passive – Artificial
Pre‑formed antibodies given as serum or monoclonal therapy
No
Days to weeks
Rabies immune globulin after exposure
Suggested diagram: Flowchart showing the four categories of immunity (Active‑Natural, Active‑Artificial, Passive‑Natural, Passive‑Artificial) with examples.
Key Points to Remember
Active immunity involves the host’s own immune response and creates memory; passive immunity provides immediate but temporary protection.
Natural immunity arises from everyday exposure; artificial immunity is deliberately induced by medical intervention.
Vaccination is a form of active artificial immunity designed to mimic natural infection without causing disease.
Passive artificial immunity is crucial for post‑exposure prophylaxis when there is no time for an active response.