BACKGROUND Host immune responses are classically divided into innate immune
responses, which react rapidly and nonspecifically upon encountering a pathogen, and …

Highlights•Organisms lacking an adaptive immune system can mount resistance to
secondary infections.•NK cells and monocytes have adaptive (memory) characteristics.• …

Immune responses in vertebrates are classically divided into innate and adaptive, with only
the latter being able to build up immunological memory. However, although lacking adaptive …

The inability of innate immunity to build an immunological memory is considered a main
difference with adaptive immunity. This concept has been challenged by studies in plants …

Traditionally, the innate and adaptive immune systems are differentiated by their specificity
and memory capacity. In recent years, however, this paradigm has shifted: Cells of the …

Immune memory is a defining feature of the acquired immune system, but activation of the
innate immune system can also result in enhanced responsiveness to subsequent triggers …

The innate arm of the immune system has generally been regarded as primitive and non-
specific and, in contrast to adaptive immunity, not to possess memory. Here we review the …

Highlights•In recent years, the ability to form immunological memory has been described in
many taxa, including plants, invertebrates, and vertebrates.•Innate immune and non-immune …

Trained immunity is a de facto memory for innate immune responses, leading to long-term
functional reprogramming of innate immune cells. In physiological conditions, trained …

The innate immune system is able to build memory-like features in response to certain
infections or vaccines, resulting in enhanced responsiveness upon (re) challenge with the …