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The specific (adaptive) immune response is activated when pathogens breach the non-specific defences. It involves lymphocytes — B cells and T cells — that recognise specific antigens and mount a targeted response. This lesson covers the roles of B cells and T cells, antigen presentation, clonal selection, and the cell-mediated and humoral immune responses for the Edexcel A-Level Biology (9BI0) specification.
An antigen is any molecule (usually a protein or glycoprotein) that is recognised by the immune system and can trigger an immune response.
| Type | Description | Example |
|---|---|---|
| Foreign antigens | Molecules on the surface of pathogens, toxins, or foreign cells | Bacterial cell wall proteins, viral capsid proteins, pollen proteins |
| Self-antigens | Molecules on the surface of the body's own cells | MHC (Major Histocompatibility Complex) proteins — unique to each individual |
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