Abstract
The interactions between a human CD4 F T cell clone and monocyte-derived human dendritic cells (DC) were analyzed with an imaging system. The first question addressed was the relationship between the formation of a contact zone and the triggering of a Ca 2F response in the T cells, in the presence or absence of antigen. Interaction of T cells with DC pulsed with the antigen led to the formation of a stable contact zone, followed by the appearance in the T cells of large and sustained Ca 2F oscillations. In the absence of antigen, contact zones formed normally and, surprisingly, Ca 2F responses were also observed, characterized by rare and small transients. Antigen-independent Ca 2F responses were not MHC restricted. The possible influence of Ca 2F responses in the DC on the efficiency of antigen presentation was then investigated. In DC, Ca 2F responses can be elicited by a variety of stimuli: cell adhesion, platelet-activating factor, UTP and chemotactic molecules (formyl-Met‐Leu‐Pro, RANTES, MIP-1b and SDF-1a). Importantly, Ca 2F responses were also induced in ~30% of DC as a result of their interaction with T cells. However, the efficiency of antigen presentation (as judged by the percentage of T cells presenting a Ca 2F response) was independent of the Ca 2F level in DC. Thus, imaging the interactions between human T cells and DC led us to observe two novel phenomena: DC-induced but antigen-independent Ca 2F responses in T cells and T cell-induced Ca 2F responses in DC.
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