Innate immune memory: Time for adopting a correct terminology

The concept of innate immune memory, i.e., a change in the reactivity in innate immune cells previously exposed to various stimuli, is well known in plants, invertebrates and also in vertebrates (1). Innate immune memory differs from adaptive memory for many aspects, including the lack of gene rearrangements, the involvement of epigenetic reprogramming, the type of cells involved (innate cells vs. T and B lymphocytes), and the receptors engaged in pathogen/antigen recognition [selective pattern-recognition receptors (PRR) vs. antigen-specific T cell and B cell receptors]. In general, although debatable, innate memory is considered as a non-specific short-lived phenomenon, as opposed to adaptive memory that is long-lived and highly specific. In plants, innate memory is known as systemic acquired resistance (SAR). In SAR, a localized infectious stimulus recognized by PRR induces systemic resistance to subsequent challenges with the same or unrelated stimuli (2). This "broad spectrum" resistance is the major immune mechanism in plants and is very similar to innate immunity and innate memory in other organisms (3).