The nonspecific face of adaptive immunity

- Live vaccines may confer protection against non-targeted pathogens.
- This process involves reprogramming of both innate and adaptive cells.
- T cell may differentiate into memory cells without classical antigenic activation.
- The complete immunological history shapes the nature of the response to infection.

Memory T cells generated by infection or immunization persist in the organism and mediate specific protection upon rechallenge with microbial pathogens expressing the same molecular structures. However, multiple lines of evidence indicate that previously encountered or persisting pathogens influence the immune response to unrelated pathogens. We describe the acquisition of non-antigen specific memory features by both innate and adaptive immune cells explaining these phenomena. We also focus on the different mechanisms (homeostatic or inflammatory cytokine-driven) that lead to acquisition of memory phenotype and functions by antigen-inexperienced T lymphocytes. We discuss the implications of these new concepts for host defense, auto-immunity and vaccination strategies.