Abstract: Foxp3(+)CD4(+)CD25(high) regulatory T cell (Treg) suppression of inflammation depends on T-cell receptor-mediated Nuclear Factor of Activated T cells c1 (NFATc1) activation with reduced Akt activity. We investigated the role of the scaffold protein Disc large homolog 1 (Dlgh1) in linking the T-cell receptor to this unique signaling outcome. The Treg immunological synapse (IS) recruited fourfold more Dlgh1 than conventional CD4(+) T-cell IS. Tregs isolated from patients with active rheumatoid arthritis, or treated with tumor necrosis factor-α, displayed reduced function and diminished Dlgh1 recruitment to the IS. Furthermore, Dlgh1 silencing abrogated Treg function, impaired NFATc1 activation, reduced phosphatase and tensin homolog levels, and increased Akt activation. Dlgh1 operates independently of the negative feedback pathway mediated by the related adapter protein Carma1 and thus presents an array of unique targets to selectively manipulate Treg function.
Abstract: The initial engagement of the TCR through interaction with cognate peptide-MHC is a requisite for T cell activation and confers Ag specificity. Although this is a key event in T cell activation, the duration of these interactions may affect the proliferative capacity and differentiation of the activated cells. In this study, we developed a system to evaluate the temporal requirements for antigenic stimulation during an immune response in vivo. Using Abs that target specific Ags in the context of MHC, we were able to manipulate the duration of Ag availability to both CD4 and CD8 T cells during an active infection. During the primary immune response, the magnitude of the CD4 and CD8 T cell response was dependent on the duration of Ag availability. Both CD4 and CD8 T cells required sustained antigenic stimulation for maximal expansion. Memory cell differentiation was also dependent on the duration of Ag exposure, albeit to a lesser extent. However, memory development did not correlate with the magnitude of the primary response, suggesting that the requirements for continued expansion of T cells and memory differentiation are distinct. Finally, a shortened period of Ag exposure was sufficient to achieve optimal expansion of both CD4 and CD8 T cells during a recall response. It was also revealed that limiting exposure to Ag late during the response may enhance the CD4 T cell memory pool. Collectively, these data indicated that Ag remains a critical component of the T cell response after the initial APC-T cell interaction.
Abstract: In response to infection, CD8(+) T cells integrate multiple signals and undergo an exponential increase in cell numbers. Simultaneously, a dynamic differentiation process occurs, resulting in the formation of short-lived effector cells (SLECs; CD127(low)KLRG1(high)) and memory precursor effector cells (CD127(high)KLRG1(low)) from an early effector cell that is CD127(low)KLRG1(low) in phenotype. CD8(+) T cell differentiation during vesicular stomatitis virus infection differed significantly than during Listeria monocytogenes infection with a substantial reduction in early effector cell differentiation into SLECs. SLEC generation was dependent on Ebi3 expression. Furthermore, SLEC differentiation during vesicular stomatitis virus infection was enhanced by administration of CpG-DNA, through an IL-12-dependent mechanism. Moreover, CpG-DNA treatment enhanced effector CD8(+) T cell functionality and memory subset distribution, but in an IL-12-independent manner. Population dynamics were dramatically different during secondary CD8(+) T cell responses, with a much greater accumulation of SLECs and the appearance of a significant number of CD127(high)KLRG1(high) memory cells, both of which were intrinsic to the memory CD8(+) T cell. These subsets persisted for several months but were less effective in recall than memory precursor effector cells. Thus, our data shed light on how varying the context of T cell priming alters downstream effector and memory CD8(+) T cell differentiation.
Abstract: T cell activation and function require a structured engagement of antigen-presenting cells. These cell contacts are characterized by two distinct dynamics in vivo: transient contacts resulting from promigratory junctions called immunological kinapses or prolonged contacts from stable junctions called immunological synapses. Kinapses operate in the steady state to allow referencing to self-peptide-MHC (pMHC) and searching for pathogen-derived pMHC. Synapses are induced by T cell receptor (TCR) interactions with agonist pMHC under specific conditions and correlate with robust immune responses that generate effector and memory T cells. High-resolution imaging has revealed that the synapse is highly coordinated, integrating cell adhesion, TCR recognition of pMHC complexes, and an array of activating and inhibitory ligands to promote or prevent T cell signaling. In this review, we examine the molecular components, geometry, and timing underlying kinapses and synapses. We integrate recent molecular and physiological data to provide a synthesis and suggest ways forward.
Abstract: The factors controlling the progression of an immune response to generation of protective memory are poorly understood. We compared the in situ and ex vivo characteristics of CD8 T cells responding to different forms of the same immunogen. Immunization with live Listeria monocytogenes, irradiated L. monocytogenes (IRL), or heat-killed L. monocytogenes (HKL) induced rapid activation of CD8 T cells. However, only IRL and live L. monocytogenes inoculation induced sustained proliferation and supported memory development. Gene and protein expression analysis revealed that the three forms of immunization led to three distinct transcriptional and translational programs. Prior to cell division, CD8 T cell-dendritic cell clusters formed in the spleen after live L. monocytogenes and IRL but not after HKL immunization. Furthermore, HKL immunization induced rapid remodeling of splenic architecture, including loss of marginal zone macrophages, which resulted in impaired bacterial clearance. These results identify initial characteristics of a protective T cell response that have implications for the development of more effective vaccination strategies.
Abstract: The factors involved in the differentiation of memory CD4 T cells from naïve precursors are poorly understood. We developed a system to examine the effect of increased competition for antigen by CD4 T cells on the generation of memory in response to infection with a recombinant vesicular stomatitis virus. Competition was initially regulated by increasing the precursor frequency of adoptively transferred naïve T cell antigen receptor transgenic CD4 T cells. Despite robust proliferation at high precursor frequencies, memory CD4 T cells did not develop, whereas decreasing the input number of naïve CD4 T cells promoted memory development after infection. The lack of memory development was linked to reduced blastogenesis and poor effector cell induction, but not to initial recruitment or proliferation of antigen-specific CD4 T cells. To prove that availability of antigen alone could regulate memory CD4 T cell development, we used treatment with an mAb specific for the epitope recognized by the transferred CD4 T cells. At high doses, this mAb effectively inhibited the antigen-specific CD4 T cell response. However, at a very low dose of mAb, primary CD4 T cell expansion was unaffected, although memory development was dramatically reduced. Moreover, the induction of effector function was concomitantly inhibited. Thus, competition for antigen during CD4 T cell priming is a major contributing factor to the development of the memory CD4 T cell pool.
Abstract: CD4 T cells are not thought to play a significant role in generating an effective primary CD8 T cell response to most viral infections. We have challenged this view by demonstrating that antigen-specific CD4 T cells can indeed suppress the proliferation of antigen-specific naive CD8 T cells in response to low doses of vesicular stomatitis virus. This finding is in contrast to the established observations that at high antigen loads CD4 T cells play little role in generating CD8 T cell responses, and that in non-infectious model systems CD4 T cells actually help the CD8 T cell response. Our results suggest that at low infectious doses, CD4 T cells play a much larger role in controlling infections than previously appreciated.
Abstract: Memory T cells are distributed throughout the body following infection, but the migratory dynamics of the memory pool in vivo is unknown. The ability of circulating microbe-specific memory T cells to populate lymphoid and nonlymphoid tissues was examined using adoptive transfer and parabiosis systems. While migration of memory CD8 T cells to lymph nodes and peritoneal cavity required G(i)-coupled receptor signaling, migration to the spleen, bone marrow, lung, and liver was independent of this pathway. Following parabiosis, memory T cells rapidly equilibrated into the lymphoid tissues, lung, and liver of each parabiont, implying most memory cells were not obligately tissue resident. Equilibration of memory cell populations was delayed in the brain, peritoneal cavity, and intestinal lamina propria, indicating controlled gating for entry into these tissues. In addition, memory cell migration to the lamina propria required beta7 integrins. Thus, the blood-borne T cell pool serves to maintain the homeostasis of tissue-based memory populations.
