Types of Immunity (Cambridge International A-Level Biology)

Spec point — 11.2.4 · describe the differences between active immunity and passive immunity and between natural immunity and artificial immunity

Types of immunity

Active immunity

• Active immunity is acquired when an antigen enters the body triggering a specific immune response (antibodies are produced)

• Active immunity can be:

  • Naturally acquired through exposure to microbes
  • Artificially acquired through vaccinations

• The body produces memory cells, along with plasma cells, in both types of active immunity

  • This gives the person long-term immunity

• In active immunity, during the primary response to a pathogen (natural) or to a vaccination (artificial), the antibody concentration in the blood takes one to two weeks to increase.

• If the body is invaded by the same pathogen again or by the pathogen that the person was vaccinated against then, during the secondary response, the antibody concentration in the blood:

  • Takes a much shorter period of time to increase
  • Is higher than after the vaccination or first infection

The primary and secondary response to the same antigen

Passive immunity

• Passive immunity is acquired without an immune response

  • Antibodies are not produced by the infected person

• As the person’s immune system has not been activated, there are no memory cells that can produce antibodies in a secondary response

  • If a person is reinfected they would need another infusion of antibodies

• Depending on the disease a person is infected with (e.g., tetanus) they may not have time to actively acquire the immunity (there is no time for active immunity to occur)

• Passive immunity occurs either artificially or naturally

  • Artificial passive immunity occurs when:

    • People are given an injection / transfusion of the antibodies—in the case of tetanus this is an antitoxin
    • The antibodies were collected from people whose immune system had been triggered by a vaccination to produce tetanus antibodies

  • Natural passive immunity occurs when:

    • Foetuses receive antibodies across the placenta from their mothers
    • Babies receive the initial breast milk from mothers (the colostrum) which delivers a certain type of antibody (IgA)

Exam Hint Active immunity is when the body produces the antibodies, whereas in passive immunity the body is given the antibodies.