After the physical barriers what is the first line of defense in the body?

After physical barriers like skin and mucous membranes, the first line of defense in the body is the innate immune system, which includes various immune cells and proteins that respond rapidly to pathogens. Key components include phagocytes, such as macrophages and neutrophils, which engulf and destroy invaders, as well as natural killer cells that target infected or cancerous cells. Additionally, the release of antimicrobial proteins and the inflammatory response help to contain and eliminate threats. This immediate response is crucial for controlling infections before the adaptive immune system is activated.