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Name of Direct Supervisor: Antonio Lanzavecchia, MD
Location: Laboratory of Immune Regulation
Descriptive title of the research activity: B and T cell activation, migration and memory.
Overall goals: Our group is interested in understanding how signaling from antigen receptors, costimulatory molecules and cytokines determines lymphocyte fate, with emphasis on the acquisition and maintenance of immunological memory. Our working hypothesis is that lymphocyte differentiation is a progressive process determined by the cumulative strength of stimulation (i.e. intensity and duration) resulting from the stochastic exposure of T cells to antigen presenting cells and cytokines.
Rationale and Significance: A clear-cut relationship exists between the number of antigen-carrying DC migrated to the draining lymph node and the magnitude and type of T cell response. High DC number increase the probability of DC-T cell encounter, deliver a sustained stimulation through monogamous or successive interactions and reduce competition among T cells for access to antigen presenting cells. We investigated the parameters that affect the migration of subcutaneously injected mouse mature DC to the draining lymph nodes. We found that mature DC that reached the lymph node, but not CCR7-deficient DC that did not, efficiently induced a sustained shut down of lymphocyte traffic in the draining lymph node, which was proportional to the number of migrating DC.
We also found that the efficiency of DC migration could be regulated at the level of lymphatic endothelium by inflammatory cytokines that upregulated expression of the CCR7 ligand CCL21/SLC in lymphatic endothelial cells. The magnitude and quality of CD4+ T cell responses was proportional to the number of antigen-carrying DC that reached the lymph node and could be boosted up to 40-fold by conditioning the tissue for increased DC migration. These results indicate that tissue inflammation facilitates DC migration to the draining lymph node and indicate novel strategies to improve DC-based therapies.
Description of work and methodology: We will adoptively transfer CFSE labelled CD4+ (DO11.10) or CD8+ (OT-I) ovalbumin (OVA) specific transgenic T cells into syngeneic or F1 mice. The mice will be challenged with graded numbers of DC (induced to mature by different stimuli such as LPS, CpG, CD40L, PGE2) either subcutaneously or intravenously. The kinetics of T cell division, the number of dividing cells and their properties will be monitored. In particular we will evaluate the migratory capacity of T cells generated to discriminate between tissue homing and lymph node homing cells. The generation of memory cells will be evaluated by following the immune response through the contraction phase in both secondary lymphoid organs and inflamed peripheral tissues. In particular, we will test two alternative models for memory T cell generation by rigorously testing in vitro and in vivo whether and under which conditions differentiated cells that have lost CCR7 and L-selectin can reacquire both lymph node homing receptors. Quantitative data will be generated and will be used to implement a mathematical model that they have already developed for B cell responses. In particular we will consider the following parameters: i) number and type of DC injected; ii) maturation stimulus and kinetics (active versus exhausted DC); iii) the route of injection i.e subcutaneous route with or without tissue conditioning versus intravenous route; iv) the number and type of responding T cells (CD4 and CD8 alone or in combination); v) the role of T helper memory cells and regulatory cells in CD4 and CD8 T cell priming.
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