Innate Recognition and Immune Modulation in Fish Trained Immunity

The first thing that comes to mind with the word trained immunity is the immunological training every immune cell acquired during the entire lifespan of an individual including fish. However according to recent concept, trained immunity is the mechanism of immunological memory of innate immune cells unlike adaptive immune response which involves memory cell generation. Instead innate immune cells create memory through epigenetic modifications and metabolic rewriting and many other concepts that are emerging out in recent years. Establishing the concept of trained immunity in fish presents unique challenges. This is primarily because the fish immune system operates as an integrated network, unlike the compartmentalized approach often used in studying immunology, vaccinology, nutrition, epigenetics, genetics, and biochemistry. These interconnected systems make it difficult to isolate and study the mechanisms underlying trained immunity.

To advance our understanding of trained immunity in fish, it is essential to disentangle it from related concepts such as immunological training, vaccine-induced immunity, epigenetic modifications, and metabolic reprogramming. Specifically, we need to: (1) Clarify the mechanisms of innate immune cell training and justify limiting this training to early developmental stages; (2) Establish trained immunity through epigenetic modifications, while demonstrating that epigenetic factors influence macrophages and related innate immune cells only within specific timeframes; (3) Validate trained immunity through metabolic reprogramming, ensuring that nutrient influences on innate immune status are accounted for; (4) Reconsider the roles of immunostimulants and vaccines, ensuring that their effects are restricted to innate immune cells and do not overlap with adaptive immunity; (5) Evaluate the genetic and species-specific influences on the immune system, including the potential for maternal transfer of genetic and epigenetic information.

This Research Topic invites both research and review articles that address the following areas:

• Innate Immune Cell Training: Studies targeting monocytes in in-vitro systems exposed to various pathogens or pathogen-associated molecular patterns (PAMPs), focusing on related gene expression (e.g., complement and its receptors, toll-like receptors, lectins, integrins, etc.).
• Vaccination Trials: Research and reviews demonstrating that vaccine doses influence innate immune cells without affecting adaptive immunity.
• Genetic and Epigenetic Factors: Investigations into the genetic and epigenetic responses of fish to pathogens or PAMPs, from early developmental stages to breeding, including maternal transfer of acquired genetic and epigenetic traits to offspring.
• Disease-Specific Immunity: Studies focusing on immune repertoires involved in disease susceptibility and survival in specific fish species, with an emphasis on genetic-assisted selection to develop resistant varieties.
• Metabolic Reprogramming: Research targeting trained immunity through metabolic rewriting mechanisms.
• Immunostimulation: Studies exploring the role of immunostimulants in inducing trained immunity.