Blood Journal
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Brief report
How many dendritic cells are required to initiate a T-cell response?

  1. Susanna Celli1,2,
  2. Mark Day3,
  3. Andreas J. Müller1,2,
  4. Carmen Molina-Paris3,
  5. Grant Lythe3, and
  6. Philippe Bousso1,2
  1. 1Institut Pasteur, Dynamics of Immune Responses Unit, Paris, France;
  2. 2Inserm U668, Paris, France; and
  3. 3Department of Applied Mathematics, University of Leeds, Leeds, United Kingdom


T-cell activation in lymph nodes relies on encounters with antigen (Ag)–bearing dendritic cells (DCs) but the number of DCs required to initiate an immune response is unknown. Here we have used a combination of flow cytometry, 2-photon imaging, and computational modeling to quantify the probability of T cell–DC encounters. We calculated that the chance for a T cell residing 24 hours in a murine popliteal lymph nodes to interact with a DC was 8%, 58%, and 99% in the presence of 10, 100, and 1000 Ag-bearing DCs, respectively. Our results reveal the existence of a threshold in DC numbers below which T-cell responses fail to be elicited for probabilistic reasons. In mice and probably humans, we estimate that a minimum of 85 DCs are required to initiate a T-cell response when starting from precursor frequency of 10−6. Our results have implications for the rational design of DC-based vaccines.

  • Submitted January 31, 2012.
  • Accepted August 31, 2012.
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