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  1. The immune system: Cells, tissues, function, and disease

  2. The Immune System | Johns Hopkins Medicine

  3. Immune system | healthdirect

  4. The immune system review (article) | Khan Academy

  5. How the Immune System Works - Verywell Health

  6. Immune system | Description, Function, & Facts | Britannica

  7. Overview of the Immune System - Immune Disorders - Merck …

  8. In brief: How does the immune system work?

  9. Immune system - Wikipedia

  10. Overview of the Immune System - National Institute of Allergy …