BDNF is released via the microglial phosphatidylinositol 3-kinase/BDNF signalling pathway and is essential for neuronal growth, learning and memory.99‐102 It has been shown that decreased levels of BDNF are associated with Alzheimer’s disease, suggesting that BDNF may be useful in the prevention of AD.99 Whilst this review is limited to the role of BDNF as a microglial-derived neurotrophic factor as an example, it is important to recognize that there are various other microglial-derived neurotrophic factors that are affected by microglial count and may play a role in Alzheimer’s disease. Here, BDNF is linked to Alzheimer disease.