Functional antigen-independent synapses formed between T cells and dendritic cells

Immunological synapse formation is usually assumed to require antigen recog nition by T cell receptors. However, the immunological synapse formed at th e interface between naive T cells and dendritic cells (DCs) has never been described. We show here that in the absence of antigen, and even of major h istocompatibility complex molecules,T cell-DC synapses are formed and lead to several T cell responses: a local increase in tyrosine phosphorylation, small Ca2+ responses, weak proliferation and long-term survival. These resp onses are triggered more readily in CD4(+)T cells than in CD8(+)T cells, wh ich express a specific isoform of the repulsive molecule CD43. These phenom ena may play a major role in the maintenance of the naive T cell pool in vi vo.