Adaptive Immunity

Abstract

Two fundamental features characterize adaptive immunity: specific antigen recognition and immunological memory development. Thus, B and T cells form the adaptive immune system that detects and fights infection and disease with specificity. B- and T-cell progenitors rearrange their specific receptors (BCR and TCR, respectively) generating a great variability in the antigen recognition domains. The BCR and its secreted form (antibodies) recognize antigens in their native form and induce humoral immune responses. By contrast, the TCRs bind to antigens processed and presented on major histocompatibility complex (MHC) molecules and develop cellular immune responses. Through the development of both B and T memory cells, subsequent encounters with the antigen induce more efficient and faster immune responses, being this the basis for vaccination. Fish constitute the first animal group in which most basic elements of the adaptive immune system are present. Still, given the great diversity of fish, many fundamental differences exist among different species. Likewise, the fish adaptive immune system shows some unique features. These structural and functional differences with their mammalian counterparts anticipate important differences in the way that fish regulate both humoral and cellular adaptive immune responses. In the present chapter, we provide an overview of the basic organization of the adaptive immune system in fish, highlighting its main specific traits and providing some insights as to how these particularities might condition the response to antigens.