Innate and adaptive immunity কী?

The immune system is the set of organs, cells and molecules that defend the body against infection and damage. It has two parts. Innate immunity is present from birth, acts within minutes to hours, recognises broad classes of intruders — bacteria, viruses, fungi, damaged cells — by features they share, and responds the same way every time. Adaptive immunity takes days to act, recognises each intruder individually, and remembers it (Chapter 34). The innate system is shared by all animals; the adaptive one exists only in vertebrates, and depends on the innate one to be triggered.