Harnessing interleukin 2 (IL-2) family power in fish; study of rainbow trout IL-2, IL-15, IL-15L and IL-15Ralpha

• Applicant: Privatdozent Dr. Uwe Fischer
• Subject Area: Veterinary Medical Science ; Developmental Biology ; Immunology
• Term: from 2016 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 317850006

Interleukins (ILs) are a group of cytokines that control many immune functions. In mammals, IL-2 and IL-15 are potent growth factors for cytotoxic, T helper and B cells. These cytokines are also involved in the formation and maintenance of immunological memory. Fishes, like other vertebrates, possess an immunological memory and thus can be vaccinated. In mammals, proper function of IL-15 is ensured in association with the IL-15 receptor (R) alpha chain. The function of another related cytokine, IL-15 like (IL-15L), remains unclear even in higher vertebrates. The original project was supported by the DFG to study the effect of IL-2 family cytokines in association with IL-15Ralpha in rainbow trout. The main conclusions from this project were: - fusion of IL-15 and IL-15L to sIL-15Ralpha (RLI) enhances cytokine secretion;- IL-15-RLI efficiently stimulates cytotoxic NK cells and lymphocytes from mucosal organs;- main IL-15L-RLI targets CD4-CD8-IgM- cells;- IL-2 family cytokines differently stimulate the developmental stages of trout thymocytes.However, our most fundamental discovery was that IL-15 triggers type 1 and that, in contrast, IL-15L induces type 2 immune gene transcription. Now, the functional relevance of these latter observations remains to be shown in vivo. Thus, in the project renewal, I apply for finalizing our work on in vivo immune responses behind these type 1 and type 2 triggers: cell-mediated cytotoxicity and antibody responses, respectively. Special attention will be given to the capacity of trout IL-2 family cytokines to extend the immunological memory after vaccination to overcome the short term-protection of current fish vaccines. These studies will be backed by whole immune transcriptome analysis and provide complex insights into immune pathway regulation. To address this final goal we have available six essential toolboxes:- clonal trout, a major aquacultured species, as model organism;- established platform for cytokine production;- trout leukocyte markers;- functional assays;- infection models;- whole transcriptome platform.This toolbox enables us to pursue the following main objectives: (1) in vitro cytotoxic activity of leukocytes isolated from cytokine-treated fish and (2) in vivo effects of cytokines on immune cell dynamics in naïve fish; on the outcome of viral and bacterial infections; on the effects on long-term protection and immune memory.The project renewal application aims at a duration of 24 months. The main justifications for this duration is the time needed to study immune memory since decline of vaccine-induced protection usually starts approx.12 months after immunization. Considering the time needed to produce recombinant cytokines, to get the approval for animal experiments from the ethics commission, to vaccinate and challenge (viral and bacterial) the fish and to acquire and analyse the data, I believe that a project duration of 24 months is justifiable.

• DFG Programme: Research Grants