Fill in the missing letters in the paragraph.
The number of underlines shows how many letters you need to fill in. You may answer with the full word or only the missing part.

To protect the body from harmful microorganisms, complex def _ _ _ _ mechanisms have evolved over time. The immune system can det _ _ _ invading path _ _ _ _ _ and differentiate between harmful substances and the body’s own cells. When a threat is identified, immune responses are act _ _ _ _ _ _ to eliminate the pathogen and limit potential damage. Some immune reactions occur rapidly and nonspecifically, while others develop more sl _ _ _ _ and target specific threats. If immune regulation fails, the system may mis _ _ _ _ _ _ _ attack healthy tis _ _ _ , leading to autoimmune dis _ _ _ _ _ _ .