Multigenerational immune priming in an invertebrate parthenogenetic Artemia to a pathogenic Vibrio campbellii.

Invertebrates were traditionally thought to rely on the innate arm of the defense system to fight against pathogens [1,2], and adaptivity or memory of immune responses were previously considered the hallmark of a highly evolved immune system, only present in vertebrates [3]. However, there are now evidences indicating that invertebrates have immunological specificity and memory of a kind that is a functional equivalent of adaptive immunity in vertebrates [4]. These claims for adaptive-like immunity in invertebrates were based largely on a few (phenomenological) observations that previous exposure to pathogen and/or immune elicitor (like lipopolysaccharide, heat shock protein, glucan) has a positive impact on the immune system components [5e8] and on the resistance of the animals against subsequent microbial attacks [9,10]. This form of memory in an invertebrate is termed ‘immune priming’, which is broadly defined as increased protection to a pathogen following previous exposure to a pathogen or an immune elicitor. A few recent studies have indicated that similar to vertebrate adaptive immunity, the immune priming phenomenon in