We hypothesized that CSF IL-3 was associated with CSF sTREM2 and AD pathology as well as cognitive change and that association of CSF IL-3 and CSF sTREM2, as reflected in astrocyte–microglia communication, may be a key part of the progression of AD pathology, and even with subsequent cognitive impairment. The gene discussed is IL3; the disease is Alzheimer disease.