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Learn9700Paper 2 · AS Level Structured QuestionsImmunityImmune response and vaccination
Immunity · Subtopic 1 of 1

Immune Response and Vaccination

Phagocytes (neutrophils, macrophages) engulf pathogens; macrophages become antigen-presenting cells. T-helper cells with complementary receptors are activated and release cytokines. B cells with complementary receptors undergo clonal selection and expansion, forming plasma cells (secrete antibodies) and memory cells. Cytotoxic T cells kill infected cells. Antibodies: four polypeptide chains (2 heavy, 2 light), variable regions with two antigen-binding sites, held by disulfide bonds; cause agglutination, neutralisation and opsonisation. The secondary response is faster and larger because of memory cells. Active immunity (own antibodies; natural infection or vaccination) is long-lasting; passive (given antibodies; placenta, milk, injection) is short-term. Herd immunity protects the unvaccinated. Monoclonal antibodies target specific antigens for diagnosis and treatment.

Cambridge 9700 Paper 1Cambridge 9700 Paper 2Edexcel YBI11 WBI14AQA 7402 Paper 1≈ 50 minRevision 1 · updated 2026-11-02
Section 1 of 14

Learning objectives

  • Describe phagocytosis and antigen presentation.
  • Describe B and T cell responses.
  • Relate antibody structure to function.
  • Compare types of immunity and explain vaccination.
Pause and think

Why do you usually catch chickenpox only once?

Section 2 of 14

Core idea

Start hereA body that remembers

Catch measles once and you're protected for life. Your immune system keeps a record.

The big idea

Lymphocytes with complementary receptors are selected and cloned; memory cells make the next response faster and larger.

The specific immune response

Humoral and cell-mediated responses.

Worked exampleTypes of immunity

Classify: (a) measles vaccine; (b) antibodies in breast milk.

Goal
Type.
Strategy
Made or given? Natural or artificial?
  1. (a) own antibodies, deliberate\text{(a) own antibodies, deliberate}
    Artificial active.
  2. (b) antibodies received, natural\text{(b) antibodies received, natural}
    Natural passive.
Answer(a) artificial active; (b) natural passive.
✓ CheckOnly active immunity gives memory cells ✓.

Summary

  • Antigen presentation.
  • Clonal selection.
  • Antibodies: 4 chains, 2 binding sites.
  • Active vs passive.
Key words
Antigen
Molecule that triggers an immune response.
Memory cell
Long-lived lymphocyte that gives a rapid secondary response.
HistoryJenner, 1796. Edward Jenner used cowpox material to protect a boy against smallpox; the word "vaccine" comes from vacca, Latin for cow.
Fun factSmallpox is gone. A global vaccination campaign eradicated smallpox in 1980: the first human disease wiped out.
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