Brain defenders

CD8⁺ resident memory T cells (T_RM cells) act as a first line of defense in tissues and are able to respond rapidly to pathogens and recruit other immune cells. In the Journal of Experimental Medicine, Merkler and colleagues demonstrate the existence of a de facto population of brain-resident T_RM cells (bT_RM cells) in mice. Intracranial viral infection generates bT_RM cells that are located chiefly along barrier surfaces such as the choroid plexus or meninges and less so in the parenchmya itself. These bT_RM cells proliferate homeostatically and do not require input from the periphery for their long-term maintenance, nor are peripheral memory T cells needed for the bT_RM cells to protect the brain from reinfection. Viral reinfection prompts a rapid response from bT_RM cells marked by evidence of degranulation and interferon-γ production. Both perforin and interferon-γ are required for bT_RM cell–mediated protection. The brain can therefore harbor T_RM cells that act as an effective local barrier to viral reinfection.

J. Exp. Med. (4 July 2016) doi:10.1084/jem.20151916