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Visualizing context-dependent calcium signaling in encephalitogenic T cells in vivo by two-photon microscopy

Proc Natl Acad Sci U S A. 2017 Jul 17. pii: 201701806. doi: 10.1073/pnas.1701806114. [Epub ahead of print]

Authors/Editors: Kyratsous NI, Bauer IJ, Zhang G, Pesic M, Bartholomäus I, Mues M, Fang P, Wörner M, Everts S, Ellwart JW, Watt JM, Potter BVL, Hohlfeld R, Wekerle H, Kawakami N.
Publication Date: 2017



In experimental autoimmune encephalitis (EAE), autoimmune T cells
are activated in the periphery before they home to the CNS. On their
way, the T cells pass through a series of different cellular milieus
where they receive signals that instruct them to invade their target
tissues. These signals involve interaction with the surrounding stroma
cells, in the presence or absence of autoantigens. To portray the serial
signaling events, we studied a T-cell–mediated model of EAE combining
in vivo two-photon microscopy with two different activation reporters,
the FRET-based calcium biosensor Twitch1 and fluorescent
NFAT. In vitro activated T cells first settle in secondary (2°) lymphatic
tissues (e.g., the spleen) where, in the absence of autoantigen, they
establish transient contacts with stroma cells as indicated by sporadic
short-lived calcium spikes. The T cells then exit the spleen for the CNS
where they first roll and crawl along the luminal surface of leptomeningeal
vessels without showing calcium activity. Having crossed the
blood–brain barrier, the T cells scan the leptomeningeal space for
autoantigen-presenting cells (APCs). Sustained contacts result in
long-lasting calcium activity and NFAT translocation, a measure of full
T-cell activation. This process is sensitive to anti-MHC class II antibodies.
Importantly, the capacity to activate T cells is not a general
property of all leptomeningeal phagocytes, but varies between individual
APCs. Our results identify distinct checkpoints of T-cell activation,
controlling the capacity of myelin-specific T cells to invade and
attack the CNS. These processes may be valuable therapeutic targets.

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