Which immune response is classified as a non-specific first line of defense?

The classification of immune responses into specific and non-specific systems is fundamental to understanding how the body defends itself against pathogens. Innate immunity represents the body's first line of defense and is characterized by its non-specific nature. It includes physical barriers such as skin and mucous membranes, as well as chemical barriers like antimicrobial peptides and enzymes found in secretions.

Additionally, innate immune responses involve various cells, such as phagocytes (like macrophages and neutrophils) and natural killer cells, which act quickly to respond to pathogens without the need for prior exposure. This branch of immunity does not adapt or change in response to specific pathogens, which is what distinguishes it from adaptive immunity.

In contrast, adaptive immunity, humoral immunity, and cell-mediated immunity are all components of the specific immune response that develop over time and require exposure to specific antigens. These adaptive responses provide targeted defense but are activated after the innate response has already been engaged. Therefore, the innate immune system is the correct answer to this question as it encompasses the non-specific defenses that act as the body's initial response against pathogens.