The Innate Immune System
The innate immune system is our body’s first line of defense against pathogens. It is a generalized, non-specific defense system (meaning that the defenses protect against all pathogens).
The innate immune system defenses consist of the protective mechanisms we are born with (innate means “inborn” or “natural”). These include physical barriers like our skin and mucous membranes, chemical barriers like saliva and stomach acid, immune system cells like macrophages that are constantly on the lookout for pathogens to destroy, proteins like cytokines (chemical messengers that immune cells use to communicate with one another), and the inflammatory response (inflammation). In most cases the innate immune defenses are enough to fight off pathogens before they can cause an infection but when they aren’t, the adaptive immune system is called into action (the adaptive immune system is covered in the next lesson).
Watch the video from Crash Course to learn more about the innate immune system (the video below will only show you the best parts, but feel free to watch the whole thing if you'd like!).