Trem2−/− mice injected with AD-tau showed significantly fewer microglia cells in the mammillary area (Figure 3A,F), contralateral retrosplenial cortex (Figure 3B,G), and ipsilateral ventral hippocampus (Figure 3C,H), as well as a trend (p = 0.066) towards a lower count in the ipsilateral retrosplenial cortex (Figure 3D,I). The gene discussed is TREM2; the disease is Alzheimer disease.