​Within the brain, astrocytes play an essential role as partners for neurons and actively participate in cerebral function and plasticity. However, in pathological situations (infection, trauma, stroke, tumor, neurodegenerative disease (Alzheimer's, etc.)), these cells undergo a significant transformation that makes them "reactive." Given their numerous roles in cerebral physiology, this transformation of astrocytes to the reactive state is likely to have considerable consequences on the brain's resilience to pathological situations and influence disease course.

Astrocyte transformation is not a new discovery: it was first observed over a century ago in the postmortem brains of patients with different pathologies. Nonetheless, many aspects of it remain mysterious and controversial.

In an article entitled "Reactive astrocyte nomenclature, definitions, and future directions," published in the journal Nature Neuroscience, 81 researchers from 22 countries have established a first consensus statement on nomenclature and definitions for reactive astrocytes. They discussed and debated for more than a year to establish a stable terminology for the field, determine good research practices and identify priority questions that need answers to better understand the complex and specific responses of astrocytes to pathological conditions. Indications for characterizing the morphology of reactive astrocytes and pinpointing the markers that need to be considered for their analysis were also discussed among the authors and presented in their article. The endpoints of this effort for consensus among the field's specialists were to optimize the therapeutic targeting of reactive astrocytes in the range of pathologies involving them, and to enable their use as diagnostic and disease-course biomarkers and as stratification tools for patients with brain diseases.

The consensus article was the result of an initiative launched by Carole Escartin, head of the reactive astrocytes team at the Neurodegenerative Diseases Laboratory (MIRCen), following the publication of her review¹ in the journal Glia in 2019.  In that work, she and her team interviewed a sample of researchers to identify points of agreement and disagreement in the field, and presented an overview of current knowledge and future challenges in it.