Defining Microglial States and Nomenclature: A Roadmap to 2030

Microglial research has been constrained by a rolling series of dichotomies such as "resting versus activated" or "M1 versus M2". This Manichean perspective of good or bad microglia is in sharp contrast with the wide repertoire of microglial functions, exerted from development to aging and diseases, brought to light in recent years. New designations continuously arising in the attempt to describe different microglial states from transcriptomics or other readouts may thus easily lead to the misleading, although unintentional, coupling of categories and functions. To address these issues, we assembled a group of multidisciplinary experts in microglial research and discussed our current understanding of microglial states as a dynamic concept. In this white paper, we provide a series of recommendations on the use of microglial nomenclature for researchers, reviewers and editors, including neophytes. We discuss gaps in knowledge and future challenges to tackle, providing a conceptual framework to understand microglial states.