The Human Immune System

The human immune system is made up of different types of organs, cells, and molecules which cooperate with each other to defend the body from foreign invaders such as fungi, viruses, and bacteria, which can cause disease.

The earliest human immune system has not been well characterized, but it is known that primates have complete immune systems which are fully adapted just like humans. From this, scientists have deduced that the earliest human had an immune system much like the one humans have today.

Fish have only innate immune systems. The adaptive immune system begins to immerge in birds. All mammals have both innate and adaptive immune systems.