Answer the following question given this paragraph: 

CHAPTER SUMMARY 42.1 Innate Immune Response The innate immune system serves as a first responder to pathogenic threats that bypass natural physical and chemical barriers of the body. Using a combination of cellular and molecular attacks, the innate immune system identifies the nature of a pathogen and responds with inflammation, phagocytosis, cytokine release, destruction by NK cells, and/or a complement system. When innate mechanisms are insufficient to clear an infection, the adaptive immune response is informed and mobilized.


Q: What serves as a first responder to pathogenic threats that bypass natural physical and chemical barriers of the body?


A:
innate immune system