Summary Age-associated thymic involution results in diminished T cell output and function in aged individuals. However, molecular mediators contributing to the decline in thymic function during early thymic involution remain largely unknown. Here we present transcriptional profiling of purified thymic stromal subsets from mice 1, 3, and 6 months of age, spanning early thymic involution. The data implicate novel biological functions for a subset of thymic epithelial cells. The predominant transcriptional signature of early thymic involution is decreased expression of cell cycle associated genes and E2F3 transcriptional targets in thymic epithelial subsets. Also, expression of pro-inflammatory genes increases with age in thymic dendritic cells. Many genes previously implicated in late involution are already deregulated by 3 to 6 months of age. We provide these thymic stromal datasets, along with thymocyte datasets, in a readily searchable web-based platform, as a resource for investigations into thymocyte: stromal interactions and mechanisms of thymic involution.

Helper and cytotoxic T cells accomplish focused secretion through the clustering of vesicles around the MTOC and translocation of the MTOC to the target contact site. Here, using Jurkat cells and OT-I T cell receptor (TcR) transgenic primary murine CTLs, we show that the dynein-binding proteins NDE1 and dynactin (as represented by p150Glued) form mutually exclusive complexes with dynein, exhibit non-overlapping distributions in target-stimulated cells, and mediate different transport events. When Jurkat cells expressing a dominant negative form of NDE1 (NDE1-EGFP fusion) were activated by SEE-coated Raji cells, NDE1 and dynein failed to accumulate at the immunological synapse (IS) and MTOC translocation was inhibited. Knockdown of NDE1 in Jurkat cells or primary mouse CTLs also inhibited MTOC translocation and CTL-mediated killing. In contrast to NDE1, knockdown of p150Glued, which depleted the alternative dynein-dynactin complex, resulted in impaired accumulation of CTLA-4 and granzyme-B containing intracellular vesicles at the IS, while MTOC translocation was not affected. Depletion of p150Glued in CTLs also inhibited CTL-mediated lysis. We conclude that the NDE1/Lis1 and dynactin complexes separately mediate two key components of T cell focused secretion, namely translocation of the MTOC and lytic granules to the IS, respectively.

Maturing thymocytes enter the thymic medulla, where they encounter numerous self-antigens presented by antigen presenting cells (APC). Those thymocytes that are strongly self-reactive undergo either negative selection or diversion into the regulatory T cell lineage. Although the majority of the proteome is expressed in the medulla, many self-antigens are expressed by only a minor fraction of medullary APC; thus, thymocytes must efficiently enter the medulla and scan APC to ensure central tolerance. Chemokine receptors promote lymphocyte migration, organization within tissues, and interactions with APC in lymphoid organs. The chemokine receptor EBI2 governs localization of T cells, B cells, and dendritic cells (DC) during immune responses in secondary lymphoid organs. However, the role of EBI2 in thymocyte development has not been elucidated. Here, we demonstrate that EBI2 is expressed by murine CD4+ single positive (CD4SP) thymocytes and thymic DC. EBI2 deficiency altered the TCR repertoire, but did not grossly impact thymocyte cellularity or subset distribution. EBI2 deficiency also impaired negative selection of OT-II TCR transgenic thymocytes responding to an endogenous self-antigen. Two-photon imaging revealed that EBI2 deficiency resulted in reduced migration and impaired medullary accumulation of CD4SP thymocytes. These data identify a role for EBI2 in promoting efficient thymic central tolerance.

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