Polarized release of T-cell-receptor-enriched microvesicles at the immunological synapse.

The recognition events that mediate adaptive cellular immunity and regulate antibody responses depend on intercellular contacts between T cells and antigen-presenting cells (APCs). T-cell signalling is initiated at these contacts when surface-expressed T-cell receptors (TCRs) recognize peptide fragments (antigens) of pathogens bound to major histocompatibility complex molecules (pMHC) on APCs. This, along with engagement of adhesion receptors, leads to the formation of a specialized junction between T cells and APCs, known as the immunological synapse, which mediates efficient delivery of effector molecules and intercellular signals across the synaptic cleft. T-cell recognition of pMHC and the adhesion ligand intercellular adhesion molecule-1 (ICAM-1) on supported planar bilayers recapitulates the domain organization of the immunological synapse, which is characterized by central accumulation of TCRs, adjacent to a secretory domain, both surrounded by an adhesive ring. Although accumulation of TCRs at the immunological synapse centre correlates with T-cell function, this domain is itself largely devoid of TCR signalling activity, and is characterized by an unexplained immobilization of TCR-pMHC complexes relative to the highly dynamic immunological synapse periphery. Here we show that centrally accumulated TCRs are located on the surface of extracellular microvesicles that bud at the immunological synapse centre. Tumour susceptibility gene 101 (TSG101) sorts TCRs for inclusion in microvesicles, whereas vacuolar protein sorting 4 (VPS4) mediates scission of microvesicles from the T-cell plasma membrane. The human immunodeficiency virus polyprotein Gag co-opts this process for budding of virus-like particles. B cells bearing cognate pMHC receive TCRs from T cells and initiate intracellular signals in response to isolated synaptic microvesicles. We conclude that the immunological synapse orchestrates TCR sorting and release in extracellular microvesicles. These microvesicles deliver transcellular signals across antigen-dependent synapses by engaging cognate pMHC on APCs.

Modulation of dendritic cell trafficking to and from the airways.

We investigated the fate of latex (LX) particles that were introduced into mice intranasally. Macrophages acquired the vast majority of particles and outnumbered LX particle-bearing airway dendritic cells (DCs) by at least two orders of magnitude. Yet alveolar macrophages were refractory to migration to the draining lymph node (DLN), and all transport to the DLN could be ascribed to the few LX(+) airway DCs. Upon macrophage depletion, markedly greater numbers of DCs were recruited into the alveolar space. Consequently, the number of DCs that carried particles to the DLN was boosted by 20-fold. Thus, a so far overlooked aspect of macrophage-mediated suppression of airway DC function stems from the modulation of DC recruitment into the airway. This increase in DC recruitment permitted the development of a robust assay to quantify the subsequent migration of DCs to the DLN. Therefore, we determined whether lung DCs use the same molecules that skin DCs use during migration to DLNs. Like skin DCs, lung DCs used CCR7 ligands and CCR8 for emigration to DLN, but the leukotriene C(4) transporter multidrug resistance-related protein 1 did not mediate lung DC migration as it does in skin, indicating that pathways governing DC migration from different tissues partially differ in molecular regulation.

B cell-driven lymphangiogenesis in inflamed lymph nodes enhances dendritic cell mobilization.

Dendritic cell (DC) migration from the periphery to lymph nodes is regulated by the pattern of genes expressed by DCs themselves and by signals within the surrounding peripheral environment. Here, we report that DC mobilization can also be regulated by signals initiated within the downstream lymph nodes, particularly when lymph nodes enlarge as a consequence of immunization. Lymph node B lymphocytes orchestrate expansion of the lymphatic network within the immunized lymph node. This expanded network in turn supports increased DC migration from the periphery. These results reveal unique relationships between B cells, lymphatic vessels, and migratory DCs. Knowledge that DC migration from the periphery is augmented by B cell-dependent signals reveals new potential strategies to increase DC migration during vaccination.