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How many dendritic cells are required to initiate a T-cell response?
Susanna Celli1, Mark Day, Andreas J Müller
1Institut Pasteur, Dynamics of Immune Responses Unit, Paris, France.
Insights
A minimum number of antigen-bearing dendritic cells (DCs) are crucial for initiating T-cell activation. Below a threshold, T-cell responses fail due to probabilistic reasons, impacting vaccine design.
Area of Science:
- Immunology
- Cellular Biology
- Computational Biology
Background:
- T-cell activation is essential for adaptive immunity and occurs in lymph nodes.
- Antigen-presenting dendritic cells (DCs) are key initiators of T-cell responses.
- The precise number of DCs required to trigger T-cell activation remains undetermined.
Purpose of the Study:
- To quantify the probability of T-cell and DC encounters in lymph nodes.
- To determine the minimum number of DCs needed to initiate a T-cell response.
- To understand the probabilistic threshold for T-cell activation.
Main Methods:
- Utilized flow cytometry for cell analysis.
- Employed 2-photon imaging for in vivo visualization of cellular interactions.
- Applied computational modeling to calculate encounter probabilities.
Main Results:
- Calculated T-cell interaction probabilities with DCs at varying DC numbers (10, 100, 1000).
- Identified a threshold in DC numbers below which T-cell responses are unlikely.
- Estimated a minimum of 85 DCs are required to initiate T-cell responses in mice.
Conclusions:
- T-cell activation is dependent on a critical number of antigen-bearing DCs.
- Probabilistic limitations exist for T-cell activation at low DC frequencies.
- Findings inform the rational design of dendritic cell-based vaccines.
Abstract:
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.
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