The immunological synapse.

The immunological synapse plays a central role in organising the immune system. Through their synaptic activity both T and B cells usually, but not always, acquire the information that critically determines the level and nature of the responses that they make. For T cells much of that information comes from epicrine and paracrine cell-cell interactions in the cluster that forms around a dendritic cell. These interactions are being dissected by experiments in which two populations of TCR-transgenic T cells are combined in vivo. Another important aspect of synaptic activity is the way in which different levels of expression of MHC class II molecules influence Th1/Th2 balance. In exploring this form of control we are learning something of general importance about cis-regulation.