Subacute Sclerosing Panencephalitis: How Measles Virus Adapts to the Brain.

Measles virus (MeV) infection is mediated by two cellular receptors: signaling lymphocytic activation molecule family member 1 (SLAMF1, also known as CD150), expressed by immune cells, and nectin-4, expressed by epithelial cells. Infection of immune cells causes systemic disease and immune suppression, while infection of airway epithelial cells results in efficient transmission. In rare cases, MeV reaches the brain and slowly spreads in cells that do not express bona fide receptors, causing subacute sclerosing panencephalitis (SSPE). In the brains of persons with SSPE, multiple mutations of the MeV membrane fusion apparatus are selected that enable its triggering by host proteins acting as surrogate receptors. These mutations favor cell-to-cell spread, which promotes population-based MeV genome evolution and the formation of collective infectious units (CIUs). CIUs, which can rebalance their components and rapidly adapt to new environments, may support neuropathogenesis of other nonintegrating RNA viruses, in particular those with nonsegmented negative-strand genomes.