T cells in the central nervous system: Messengers of destruction or purveyors of protection?

Although the destructive effects of an overactive adaptive immune system have been well established, especially in the context of autoimmune diseases, recently an understanding of the beneficial effects of the adaptive immunity in central nervous system (CNS) injuries has emerged. CD4⁺ T cells have been shown to benefit injured CNS tissue through various mechanisms; both traditional cytokine signalling and by modulating the phenotype of neural cells in the injury site. One of the major targets of the cytokine signalling in the CNS are myeloid cells, both resident microglia and monocytes, that infiltrate the tissue after injury and whose phenotype; protective or destructive, appears to be directly influenced by T cells. This cross-talk between the adaptive and innate immune systems presents potential new targets that could provide tangible benefits in pathologies that currently have few treatment options.