Each type of cell has specific surface molecules that identify it, enabling the immune system to identify: pathogens; cells from other organisms of the same species; abnormal body cells; toxins
Every cell carries unique molecules on its surface, like a molecular ID badge. Your immune system reads these badges to spot anything foreign or dangerous.
Real World
During organ transplants, surgeons match donor and recipient surface molecules (HLA antigens) as closely as possible — a mismatch caused the rejection of the first human heart transplant by Christiaan Barnard's patient in 1967.
Exam Focus
List all four categories the immune system identifies (pathogens, same-species cells, abnormal cells, toxins) when 'state' questions appear — each is a separate mark.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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