Although brain microglia and macrophages and blood-derived monocytes have different embryonic origins (Goldmann et al. 2016), under a state of chronic sterile inflammation, as it occurs in BD, triggered by social defeat stress (Wohleb et al. 2011) or TNFα (D’Mello et al. 2009), immune-activated cells can migrate to the CNS. The gene discussed is TNF; the disease is Behcet disease.