Bibliometric and Visual Analysis of Trained Immunity from 2005 to 2024

Purpose: Trained immunity refers to the long-term functional adaptation of innate immune responses following an initial stimulus, representing a conceptual expansion of immune memory beyond adaptive immunity. Given the rapid expansion of this field, this study aimed to systematically map the research landscape of trained immunity and to identify major research hotspots and emerging frontiers using bibliometric approaches. Methods: Publications related to trained immunity published between 2005 and 2024 were retrieved from the Web of Science Core Collection (WoSCC). Bibliometric and visualization analyses were performed using CiteSpace, VOSviewer, and Bibliometrix to evaluate publication trends, collaboration patterns, and thematic evolution. Results: A total of 1,526 publications were included. Bibliometric indicators demonstrate a marked acceleration in research output following the formal conceptualization of trained immunity. The United States, the Netherlands, and Germany emerged as leading contributors, with Radboud University Nijmegen and the University of Bonn identified as central institutional hubs. Thematic and keyword-based analyses revealed that research hotspots have evolved along three interconnected dimensions: an expansion of cellular targets from classical myeloid cells to hematopoietic stem and progenitor cells and selected non-immune cells; sustained focus on epigenetic and metabolic reprogramming as core mechanistic axes; and a growing body of literature linking trained immunity to infectious diseases, chronic inflammation, and cancer-related applications. Conclusion: By integrating multiple bibliometric indicators, this study delineates the developmental trajectory and thematic structure of trained immunity research. The findings provide an updated overview of the field and highlight evolving research priorities, offering a reference framework for future investigations into innate immune memory and its translational potential.