Immune synapses formed with measles virus-infected dendritic cells are unstable and fail to sustain T cell activation

Interaction with dendritic cells (DCs) is considered as central to immunosuppression induced by viruses, including measles virus (MV). Commonly, viral infection of DCs abrogates their ability to promote T cell expansion, yet underlying mechanisms at a cellular level are undefined. We found that MV-infected DCs only subtly differed from LPS-matured with regard to integrin activation, acquisition of a migratory phenotype and motility. Similarly, the organization of MV-DC/T cell interfaces was consistent with that of functional immune synapses with regard to CD3 clustering and MHC class II surface recruitment. The majority of MV-DC/T cell conjugates was, however, unstable and only promoted abortive T cell activation. Thus, MV-infected DCs retain activities required for initiating, but not sustaining T cell conjugation and activation. This is partially rescued if surface expression of the MV glycoproteins on DCs is abolished by infection with a recombinant MV encoding VSV G protein instead, indicating that these contribute directly to synapse destabilization and thereby act as effectors of T cell inhibition.