Adaptive immunity – T cells, B cells and clonal selection
BiologyHealth & DiseaseAges 16–17
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Sign in to playStep by step: a macrophage presents antigen on MHC, the helper T cell with a complementary receptor is activated, clonal selection picks the matching B cell, which divides into antibody-secreting plasma cells and memory cells, and cytotoxic T cells kill virus-infected cells. A graph compares primary and secondary responses to the same or a different antigen, and an antibody diagram lets students test which antigen binds.
Lesson: Adaptive immunity: humoral and cell-mediated responses
What it shows
The model follows a specific immune response. A macrophage digests a pathogen and displays its antigen on MHC proteins. Among many helper T cells, only the one with a complementary receptor binds and releases cytokines. Among many B cells, the antigen selects the one with complementary receptors; it divides into a clone of plasma cells, which secrete antibodies, and memory cells. Cytotoxic T cells kill infected cells with perforin. The response graph uses a simple clone model: memory cells give a shorter lag and a much higher antibody peak. Antigens are drawn as shapes and numbers are relative.
How to use
In Response pathway, choose an Antigen and a Pathogen, then press Play or step with Back and Next. In steps 3, 4 and 8, tap a cell to test whether its receptor fits. In Primary and secondary response, set Second exposure day and Second exposure to, switch Log scale, and read the table. In Antibody structure, tap the antigens below the diagram to test binding; Hide labels removes the names.
Parameters you can change
- Screen Response pathway, Primary and secondary response, Antibody structure
- Antigen Antigen A (triangle), Antigen B (square), Antigen C (circle), Antigen D (cross)
- Pathogen Virus (multiplies inside cells), Bacterium (lives outside cells)
- Second exposure day 20–120 day
- Second exposure to the same antigen, a different antigen
Questions to explore
- Why is only one B cell clone selected by antigen A, although the body has a huge number of B cells?
- Why does the secondary response start sooner and produce far more antibody, but not for a different antigen?
- Why are cytotoxic T cells important against viruses but much less against bacteria living outside cells?
