Calcium responses elicited in human T cells and dendritic cell by cell-cell interaction and soluble ligands
Abstract
The interactions between a human CD4 + 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 2+ 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 2+ oscillations. In the absence of antigen, contact zones formed normally and, surprisingly, Ca 2+ responses were also observed, characterized by rare and small transients. Antigen-independent Ca 2+ responses were not MHC restricted. The possible influence of Ca 2+ responses in the DC on the efficiency of antigen presentation was then investigated. In DC, Ca 2+ , responses can be elicited by a variety of stimuli: cell adhesion, platelet-activating factor, UTP and chemotactic molecules (formyl-Met-Leu-Pro, RANTES, MIP-ॆ and SDF-1ॅ), Importantly, Ca 2+ 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 2+ response) was independent of the Ca 2+ 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 2+ responses in T cells and T cell-induced Ca 2+ responses in DC. Key words : calcium imaging, dendritic cells, T cells