The carp immune system and immune responses to pathogens

The immune system is critical for survival and fitness of any organism, protecting them from infectious agents, toxins (sterile), tissue damage and the impairment that they elicit (Magnadottir 2006, Segner et al. 2011, Uribe et al. 2011). Such protection is based on immune responses against a given threat. The first response launched can be summarized as innate immunity, the earliest barrier to infection and damage. Innate immunity’s outcome is based on a general recognition of a group of pathogens or damage signals, rather than on a particular microorganism or molecule and does not comprise long lasting immunity (Medzhitov and Janeway Jr. 2000, Magnadottir 2006). The second response comprises more specific reactions and is collectively called adaptive (or acquired) immunity. The adaptive immune response is developed during the lifetime of an organism as adaptations to infection with any given pathogen; its protection is mediated by B- and T-lymphocytes (Fig. 8.1B) and in many cases leads to immunological memory, conferring long-lasting protection against the specific pathogens that the immune system has been exposed to (Uribe et al. 2011).