Autoreactive T and B cells are regular components of the healthy immune system. It has been proposed that some of these cells might have a protective function. Recent studies support this notion by demonstrating that a) myelin-autoreactive T cells show neuroprotective effects in vivo, and b) activated antigen-specific human T cells and other immune cells produce bioactive brain-derived neurotrophic factor (BDNF) and other neurotrophic factors in vitro. Furthermore, neurotrophic factors are expressed in different types of inflammatory cells in brain lesions of patients with acute disseminated leukoencephalopathy or multiple sclerosis. It seems plausible that the immune cell-mediated import of neurotrophic factors into the central nervous system has functional consequences, with obvious implications for the therapy of multiple sclerosis and other neuroimmunological diseases.