The immune system flashcards

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What is an antigen?

A molecule, typically a protein or polysaccharide on the surface of a pathogen or foreign cell, that is recognised by the immune system and triggers an immune response.

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What is the main role of a plasma cell?

To synthesise and secrete large quantities of a specific antibody during a humoral immune response. They differentiate from B-lymphocytes.

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Differentiate between humoral and cell-mediated immunity.

Humoral immunity involves B-lymphocytes and antibodies that target pathogens in body fluids. Cell-mediated immunity involves T-lymphocytes that directly destroy infected host cells or coordinate the immune response.

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What is clonal selection?

The process where a specific antigen binds to and activates the B or T lymphocyte that has a complementary receptor, 'selecting' it for proliferation.

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Name two mechanisms by which antibodies help eliminate pathogens.

1. **Agglutination:** Clumping pathogens together. 2. **Opsonisation:** Coating pathogens to enhance phagocytosis. (Also: Neutralisation, Complement activation).

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What is the difference between active and passive immunity?

Active immunity involves the body producing its own antibodies and memory cells, providing long-term protection. Passive immunity is the acquisition of pre-made antibodies, providing immediate but short-term protection.

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How does vaccination lead to immunity?

Vaccination introduces antigens from a pathogen, stimulating a primary immune response and the production of memory cells. This confers artificial active immunity, allowing for a rapid secondary response upon future exposure.

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What is the function of cytotoxic T-cells (T killer cells)?

They identify and destroy the body's own cells that are infected with pathogens (like viruses) or have become cancerous, by releasing proteins like perforin that create pores in the cell membrane.