Bi-Directional Notch Signaling Via Signal-Sending and Signal-Receiving Microdomains of the Partnered Immunological Synapses during Th:DC Interaction.

The Notch pathway regulates adaptive immune responses, yet the temporal development of a specific molecular anatomy underlying the directionality of Notch signaling, central to cell-fate decisions, remains unknown. Using the development of the functional immune synapse (IS) of the human physiological T-helper lymphocyte (Th): Dendritic cell (DC) interaction as our model, we followed the temporal accumulation of Notch signaling components, unprocessed and processed, in the developing ThIS and the apposed DCIS of these cells by 2D and 3D immunofluorescense microscopy. Downstream Notch targets in both cell types were followed, as well. We demonstrate that Th-Notch1 receptor and DC-Notch ligands (Delta-like1, Jagged-1) cluster in their apposed central-supramolecular-activation-clusters (cSMAC), whereas DC-Notch1 receptor and Th-Notch ligands cluster in their apposed peripheral-SMAC in an anti-parallel arrangement to that seen in the cSMAC. The resultant accumulation in both cell types of processed nuclear Notch receptor, its ligands, as well as HES-1 and phosphorylated-STAT3, supports antiparallel, reciprocal Notch signal propagation in the DC-to-Th direction via the cSMAC and Th-to-DC direction via the pSMAC. The imposed asymmetric recruitment of the components of Notch pathway, therefore, provides a novel bi-directional route by which the partnered ThIS and DCIS regulate Notch-mediated immune responses. Our data indicate that terminally differentiated immune cells communicate bidirectionally using unidirectional Notch signaling platforms that are spatially segregated into reciprocally signaling microdomains. Significantly, our observations of bidirectional Notch signaling indicate that the heterologous Th:DC interaction is cooperative, requiring reciprocal information transfer across both cell types to mount an appropriate immune response.