Which type of immune response is activated immediately upon recognition of pathogens?

The immune response that is activated immediately upon recognition of pathogens is innate immunity. This type of immunity serves as the body's first line of defense against invading organisms and operates quickly, generally within minutes to hours following the detection of a pathogen.

Innate immunity involves physical barriers like skin and mucous membranes, as well as various immune cells such as neutrophils and macrophages that recognize and respond to common features of pathogens, known as PAMPs (pathogen-associated molecular patterns). Elements of innate immunity include the inflammatory response and the activation of complement proteins, which help to clear pathogens quickly before the slower adaptive immunity becomes engaged.

While adaptive immunity (sometimes referred to as specific immunity) takes longer to develop because it is based on the recognition of specific antigens and involves immune memory, innate immunity operates on general recognition mechanisms and does not rely on previous exposure to a particular pathogen. Non-specific immunity is often used interchangeably with innate immunity since it also does not target specific pathogens but rather works against a broad range of microbes.