What term refers to the collection of nonspecific barriers and cellular responses serving as the body’s first and second line of defense against pathogens?

The innate immune system refers to the collection of nonspecific barriers and cellular responses that act as the body's first and second lines of defense against pathogens. This system includes physical barriers such as skin and mucous membranes, as well as internal responses like the actions of white blood cells, inflammation, and fever. The innate immune responses are immediate and do not target specific pathogens; instead, they provide a general defense against a wide variety of threats, making them crucial in the body’s first response to infection or injury.

In contrast, the adaptive immune system is involved in a more sophisticated, targeted response that takes time to develop and is specific to particular pathogens. The lymphatic system has a role in the immune response but is primarily responsible for fluid balance and the transportation of immune cells rather than being a direct line of defense. Acquired immunity refers to the immune response developed after exposure to specific pathogens, which is distinct from the immediate and nonspecific nature of the innate immune system.