TREM2 and Alzheimer disease: Other than the two major research areas mentioned above, several diseases are being studied, including neuropathic pain (microglial-astrocyte communication) (Yu et al., 2019), multiple sclerosis (macrophage-oligodendrocyte communication) (Chiu et al., 2013), AD (Trem2-phagocytosis) (Boche and Gordon, 2022), and retinopathy (neurogenesis) (Okunuki et al., 2018; Wang et al., 2020), in which the unique role of microglia should be noted.