Immune response and vaccination sim
Give a training arm a vaccine, later meet the live pathogen, wait a day or a week at a time, watch phagocytes and lymphocytes at work in the blood, and compare the primary and secondary antibody responses of a vaccinated and an unvaccinated person on the graph.
Defence against disease: phagocytes, lymphocytes, antibodies, memory cells and vaccination · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Immune response and vaccination: a model. A nurse's training arm stands for a person. Drag the syringe to the upper arm to give the vaccine, which holds pathogens of one kind that are dead, or weakened so they cannot cause disease (or just their antigens): they carry the same antigens as the live pathogen. Drag the dropper to the graze on the forearm to meet the live pathogen. Wait a day or a week at a time. The close-up shows what happens in the blood. Phagocytes engulf and digest pathogens (phagocytosis). Lymphocytes make antibodies whose shape fits the antigen; antibodies clump pathogens together (agglutination) and mark them for phagocytes. Some lymphocytes become memory cells. The first meeting with an antigen gives a slow, small primary response; a later meeting gives a fast, large, longer-lasting secondary response, because memory cells are already there. So a vaccinated person destroys the pathogen before it can multiply enough to cause symptoms, and an unvaccinated person is ill before enough antibodies are made. Some antibodies, called antitoxins, neutralise toxins made by bacteria; they are not shown. Simplified on purpose: antibody levels are in arbitrary units (≈ a.u.) and pathogen numbers are a relative count (≈), both illustrative; one pathogen, one antigen; timings are illustrative (primary peak 13 days after the vaccine, secondary peak 6 days after the pathogen); in this model the pathogen is met at least 14 days after the vaccine, so the two responses are easy to tell apart (protection usually takes about two weeks to build); one dose only (many real vaccines need boosters). The close-up is not to scale: red cells, lymphocytes and phagocytes are drawn to scale with each other (about 7.5, 9 and 12 µm across), but pathogens are drawn about 3 times larger than a 2 µm bacterium, and antibodies and antigens far larger than real (an antibody is about 0.01 µm). Drawn antibodies and pathogens show roughly how many there are, not real numbers. The immune system is simplified to what the syllabus needs: no T cells, and much of the response really happens in lymph nodes, shown here in one close-up of the blood. Red cells are drawn bright red (oxygen-rich blood). One run is one person; a peak typed within 10 % and 1 day is accepted.
- Lit ring: where to drop the syringe or dropper
- Close-up: the blood near the arm, magnified (not to scale)
- Graph: dashed line, the symptom level
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