In experimental autoimmune encephalomyelitis (EAE), CD4(+) self-reactive T cells target myelin components of the CNS. However, the consequences of an autoaggressive T cell response against myelin for neurons are currently unknown. We herein demonstrate that EAE induced by active immunization with an encephalitogenic myelin basic protein peptide dramatically reduces the loss of spinal motoneurons after ventral root avulsion in rats. Both brain-derived neurotophic factor (BDNF)- and neurotrophin-3 (NT-3)-like immunoreactivities were detected in mainly T and natural killer (NK) cells in the spinal cord. In addition, very high levels of BDNF, NT-3, and glial cell line-derived neurotrophic factor mRNAs were present in T and NK cell populations infiltrating the CNS. Interestingly, bystander recruited NK and T cells displayed similar or higher neurotrophic factor levels compared with the EAE disease-driving encephalitogenic T cell population. High levels of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) mRNAs were also detected, and both these cytokines can be harmful to several types of CNS cells, including neurons. However, treatment of embryonic motoneuron cultures with TNF-alpha or IFN-gamma only had a deleterious effect in cultures deprived of neurotrophic factors. These results suggest that the potentially neurodamaging consequences of severe CNS inflammation are curbed by the production of several potent neurotrophic factors in leukocytes.

T cell Ig- and mucin-domain-containing molecules (TIMs) comprise a recently described family of molecules expressed on T cells. TIM-3 has been shown to be expressed on murine Th1 cell clones and has been implicated in the pathogenesis of Th1-driven experimental autoimmune encephalomyelitis. In contrast, association of TIM-1 polymorphisms to Th2-related airway hyperreactivity has been suggested in mice. The TIM molecules have not been investigated in human Th1- or Th2-mediated diseases. Using real-time (TaqMan) RT-PCR, we show that human Th1 lines expressed higher TIM-3 mRNA levels, while Th2 lines demonstrated a higher expression of TIM-1. Analysis of cerebrospinal fluid mononuclear cells obtained from patients with multiple sclerosis revealed significantly higher mRNA expression of TIM-1 compared with controls. Moreover, higher TIM-1 expression was associated with clinical remissions and low expression of IFN-γ mRNA in cerebrospinal fluid mononuclear cells. In contrast, expression of TIM-3 correlated well with high expression of IFN-γ and TNF-α. These data imply the differential expression of human TIM molecules by Th1 and Th2 cells and may suggest their differential involvement in different phases of a human autoimmune disease.

Central nervous system (CNS)-autoreactive immune responses can exert neuroprotective effects, possibly mediated via the release of neurotrophic factors from infiltrating leucocytes. Herein, we analysed neurotrophin and cytokine mRNA levels using TaqMan polymerase chain reaction in unstimulated peripheral blood mononuclear cells (PBMCs) from multiple sclerosis (MS) patients in remission and controls. We demonstrate that mRNA for brain-derived neurotrophic factor (BDNF), but not neurotrophin-3 or nerve growth factor (NGF), is readily detectable in PBMC and that levels in MS are increased by approximately 60% compared with patients with other neurological diseases or healthy subjects. These results provide additional evidence that a potentially neuroprotective facet of autoimmune inflammation is present in MS.

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