T cell activation in vivo
Encephalitogenic T cells interact productively with local APCs within the CNS. Additionally, in the CNS, infiltrated T cells were activated, which is necessary to induce clinical EAE. However, the direct link between T cell/APC interaction and T cell activation was missing due to technical limitation. To fill the gap, two distinct activation sensor proteins, Twitch-1 and NFAT-GFP, were introduced.
Intraluminal T cells, regardless of rolling or crawling, displayed an extensive cytosolic localization of ΔNFAT-GFP, indicating resting status (Fig. 5). Similarly, many extravasated TMBP-NFAT-GFP cells showed cytosolic ΔNFAT-GFP. Once TMBP-NFAT-GFP cells contacted local APCs, T cells were arrested and ΔNFAT-GFP was translocated into the nucleus (Fig. 6). Interestingly, only a fraction of the APCs has the potential to activate T cells, suggesting that local APCs are not saturated with endogenous antigens. Twitch-1 labeled T cells also similarly detected T cell activation in the CNS.
We are now applying our calcium and NFAT indicators to determine cell-to-cell interactions in the gut, the peripheral lymphatic tissues, the BBB and the CNS target tissue.