Evolution of Adaptive Immunity

Abstract Historically, two components of immunity were identified, innate and adaptive. Innate receptors recognise molecular patterns common for groups of pathogens or for common pathological changes in host cells. All animals are protected by innate immunity. In addition, in vertebrates, adaptive immunity evolved that is based on the limitless somatic diversification of lymphoid receptors and selective expansion of those receptors that match the antigen/pathogen. Moreover, somatic hypermutation of antibodies combined with antigen selection allows fine‐tuning of an antibody sequence to match the antigen. The repertoire of adaptive immune receptors in each individual differs in dependence on its life history and provides a basis for a strong memory response. Adaptive immune systems in jaw and jawless vertebrates are built on completely different receptors; immunoglobulin superfamily in jaw vertebrates and molecules with leucine‐rich repeats in jawless vertebrates. However, they are strikingly similar functionally pointing to similar evolutionary forces shaping these systems. Key Concepts: Both adaptive and innate strategies are used in organisms from bacteria to humans. Innate mechanisms provide basic protection based on evolutionary conserved features of pathogens whereas adaptive mechanisms provide immunity that is shaped by the life history of every individual. Adaptive immunity of jaw and jawless vertebrates is based on different receptors but functionally similar pointing to the same evolutionary driving forces. Combination of adaptive and innate mechanisms is necessary to provide the most comprehensive immune protection. Genome duplications played a crucial role in the origin of the adaptive immune system. Adaptive immune system coevolve with innate immune mechanisms.