Boom Posted18 Jun 2018 15:59
what happens once the t cells lock on ... its been filmed !!
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Lessons Learned from Intravital Imaging
Experiments using intravital 2-photon microscopy showed that in the steady state, a dendritic cell (DC) interacts with 500–5000 T cells per hour, which migrate within lymph nodes with a velocity of 10–12 μm per min, thereby scanning uncounted peptide/MHC complexes (25–27). Interestingly, CD4+ and CD8+ T cells employ different strategies of surveillance: The interaction times of CD4+ T cells with DCs depend on MHC class II (MHC-II) molecules while CD8+ T cells traverse a LN slower and regardless of self-peptide/MHC-I complexes. They scan 160–200 and 300 DCs per hour and, thus, stay in a lymph node approximately for half a day and a day, respectively (28). Considering natural precursor frequencies, it has been assessed that at least 85 antigen-presenting DCs per lymph node are necessary to initiate a CD4+ T cell response (29).
When confronted with a DC presenting antigen, specific T cells stop migrating and stay in touch with an individual DC for around a day (30–33). Within this period, the T cells undergo changes classically summarized as “blasting”: They increase in size, double their protein contents, increase their total RNA contents 30-fold, induce the expression of around 1300 mRNAs, and change their metabolism before proliferation ensues 24 h later (34–40).The stable interaction with one DC can be preceded by a phase of transient interactions with several APCs, the length of which is inversely correlated with APC density and antigen dose (41). Interestingly, it has been shown that, for CD8+ T cells, the phase of stable pairing with one DC is not necessarily required for expansion of effector clones, while memory differentiation is affected. These findings indicated that the memory potential of CD8+ T cells can be programed within the first 24 h of priming (36). The data also supported the relevance of observations that T cells can “memorize” sequential sub-threshold interactions with different APCs and accumulate such signals over time, perhaps via AP1 or NFAT (42–46).