Which component of the immune response is characterized by protective cells and fluids, and includes processes such as inflammation?

The second line of defense in the immune response is characterized by protective cells and fluids that act when the first line of defense, which includes physical barriers like skin and mucous membranes, is breached. This part of the immune system is often associated with various innate immune responses, including inflammation, phagocytosis, and the activation of complement proteins.

During inflammation, the body increases blood flow to the affected area, allowing more immune cells—such as neutrophils and macrophages—to reach the site of infection or injury. These cells play a crucial role in identifying and destroying pathogens, as well as facilitating the healing process.

This is distinct from the first line of defense, which primarily serves as a physical barrier, and the third line of defense, which involves the adaptive immune response characterized by specific responses to pathogens, including the activation of T and B lymphocytes and the production of antibodies.

Thus, the second line of defense is fundamental for the immediate and non-specific response to pathogens, providing critical protections through inflammation and other innate mechanisms.