I would have to say the Immune System is the third line of defense in the human body- Acquired Immunity B and T cells Lymphocytes.
1. First line of defense- Physical barriers like the skin and mucus membranes
2. Second line of defense- Phagocyte cells: These are cells that gooble up waste products
Source:
Taught Anatomy and Physiology to nursing students for over 2 years- My head
RN in NJ
Hope this helps.
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