Which statement best describes innate immunity?

Innate immunity is characterized by its non-specific nature, serving as the first line of defense against pathogens. It encompasses physical barriers such as the skin and mucous membranes, as well as cellular components like phagocytes (e.g., macrophages and neutrophils) and natural killer cells. This type of immune response operates immediately or within hours of an antigen's appearance in the body, reacting in a general manner rather than targeting specific pathogens.

The other statements focus on aspects of the adaptive immune response, which is characterized by specificity and memory. These include the involvement of antibodies, a rapid response due to memory formation from previous exposures, and a response that requires prior sensitization to specific pathogens. In contrast, the innate response does not rely on prior exposure and functions effectively without the need for previous encounters with the pathogen. This foundational understanding of innate immunity highlights its essential role in the overall immune response.