Since the ‘X’ component in the ATX(N) system represents candidate biomarkers for additional pathophysiological mechanisms, our results showed that CSF IL-3 and CSF sTREM2 were associated with AD core biomarkers and were involved in the progression from Aβ to tau pathology, and then, they represented astrocyte–microglia communication may be interesting biomarkers for the ‘X’ component. Here, MAPT is linked to Alzheimer disease.