Direct Impact of T Cells on Neurons Revealed by Two-Photon Microscopy in Living Brain Tissue

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Abstract
Encephalitogenic T cells invade the brain during neuroinflammation such as multiple sclerosis (MS), inducing damage to myelin sheaths and oligodendrocytes. Only recently, neuronal structures were reported to be a crucial target in the disease. Here, two-photon microscopy using ion-sensitive dyes revealed that within the complex cellular network of living brain tissue, proteolipid protein (PLP)-specific T cells and T cells recognizing the nonmurine antigen ovalbumin (OVA) directly and independently of the major histocompatibility complex (MHC) contact neurons in which they induce calcium oscillations. T cell contact finally resulted in a lethal increase in neuronal calcium levels. This could be prevented by blocking both perforin and glutamate receptors. For the first time, our data provide direct insight into the activity of T cells in the living brain and their detrimental impact on neurons.