Indeed, other groups have uncovered canonical markers of M1/M2 states coexpressed in individual cells after acute brain injury (68–70) and found that high Arg1 expression by microglia drives neuropathology in an AD model via immune suppression (79), underscoring the pitfalls of the existing macrophage/microglia classification framework in the nervous system. The gene discussed is ARG1; the disease is Alzheimer disease.