Intravital imaging of T cell activation in the CNS during autoimmunity

It is known that the activation of encephalitogenic T cells within the CNS is crucial step in induction of clinical EAE. Nevertheless, due to the lack of methods, T cell activation was never visualized directly in vivo. To do this, we recently introduced two different fluorescent activation sensors. One is based on nuclear factor of activated T cells (NFAT) that quickly translocates from the cytosol to nucleus after activation stimulus. By using truncated NFAT fused to GFP (∆NFAT-GFP) the distribution of NFAT in the T cells and hence their activation status can be visualized. Other sensor, Twitch1, detects changes in the intracellular calcium level, which is one of the main transmitters of T cell activation. Twitch1 consists of cyan fluorescent protein and yellow fluorescent protein which are connected by calcium sensing troponin C domain. Due to fluorescent resonant energy transfer (FRET), Twitch1 emits blue when calcium levels are low and yellow when calcium levels are elevated.