A polarizing question: do M1 and M2 microglia exist?

In the twenty-first century, microglia came of age. Their remarkable ontogeny, unique functions and gene expression profile, process motility, and disease relevance have all been highlighted. Neuroscientists interested in microglia encounter an obsolete concept, M1/M2 polarization, suggesting experimental strategies that produce neither conceptual nor technical advances. Ransohoff's Perspective argues against applying this flawed paradigm.