Jason Waithman

Dendritic Cell-Induced Memory T Cell Activation in Nonlymphoid Tissues

Secondary lymphoid organs are dominant sites of T cell activation, although many T cells are subsequently retained within peripheral tissues. Currently, these nonlymphoid compartments are viewed as sites only of effector T cell function, without the involvement of renewed induction of immunity via the interactions with professional antigen-presenting cells. We describe a method of reactivation of herpes simplex virus to examine the stimulation of tissue-resident T cells during secondary challenge. The results revealed that memory CD8+ T cell responses can be initiated within peripheral tissues through a tripartite interaction that includes CD4+ T cells and recruited dendritic cells. These findings lend evidence for the existence of a sophisticated T cell response mechanism in extra-lymphoid tissues that can act to control localized infection.

NLRC4 inflammasomes in dendritic cells regulate noncognate effector function by memory CD8 + T cells

Memory T cells exert antigen-independent effector functions, but how these responses are regulated is unclear. We discovered an in vivo link between flagellin-induced NLRC4 inflammasome activation in splenic dendritic cells (DCs) and host protective interferon-γ (IFN-γ) secretion by noncognate memory CD8+ T cells, which could be activated by Salmonella enterica serovar Typhimurium, Yersinia pseudotuberculosis and Pseudomonas aeruginosa. We show that CD8α+ DCs were particularly efficient at sensing bacterial flagellin through NLRC4 inflammasomes. Although this activation released interleukin 18 (IL-18) and IL-1β, only IL-18 was required for IFN-γ production by memory CD8+ T cells. Conversely, only the release of IL-1β, but not IL-18, depended on priming signals mediated by Toll-like receptors. These findings provide a comprehensive mechanistic framework for the regulation of noncognate memory T cell responses during bacterial immunity.

Mixed proteasomes function to increase viral peptide diversity and broaden antiviral CD8+ T cell responses.

The three proteasome subunits with proteolytic activity are encoded by standard or immunoproteasome genes. Many proteasomes expressed by normal cells and cells exposed to cytokines are “mixed”, that is, contain both standard and immunoproteasome subunits. Using a panel of 38 defined influenza A virus–derived epitopes recognized by C57BL/6 mouse CD8+ T cells, we used mice with targeted disruption of β1i, β2i, or β5i/β2i genes to examine the contribution of mixed proteasomes to the immunodominance hierarchy of antiviral CD8+ T cells. We show that each immunoproteasome subunit has large effects on the primary and recall immunodominance hierarchies due to modulating both the available T cell repertoire and generation of individual epitopes as determined both biochemically and kinetically in Ag presentation assays. These findings indicate that mixed proteasomes function to enhance the diversity of peptides and support a broad CD8+ T cell response.

Altered Immunity and Dendritic Cell Activity in the Periphery of Mice after Long-Term Engraftment with Bone Marrow from Ultraviolet-Irradiated Mice

Alterations to dendritic cell (DC) progenitors in the bone marrow (BM) may contribute to long-lasting systemic immunosuppression (>28 d) following exposure of the skin of mice to erythemal UV radiation (UVR). DCs differentiated in vitro from the BM of mice 3 d after UVR (8 kJ/m2) have a reduced capacity to initiate immunity (both skin and airways) when adoptively transferred into naive mice. Studies in IL-10−/− mice suggested that UV-induced IL-10 was not significantly involved. To investigate the immune capabilities of peripheral tissue DCs generated in vivo from the BM of UV-irradiated mice, chimeric mice were established. Sixteen weeks after reconstitution, contact hypersensitivity responses were significantly reduced in mice reconstituted with BM from UV-irradiated mice (UV-chimeric). When the dorsal skin of UV-chimeric mice was challenged with innate inflammatory agents, the hypertrophy induced in the draining lymph nodes was minimal and significantly less than that measured in control-chimeric mice challenged with the same inflammatory agent. When DCs were differentiated from the BM of UV-chimeric mice using FLT3 ligand or GM-CSF + IL-4, the cells maintained a reduced priming ability. The diminished responses in UV-chimeric mice were not due to different numerical or proportional reconstitution of BM or the hematopoietic cells in blood, lymph nodes, and skin. Erythemal UVR may imprint a long-lasting epigenetic effect on DC progenitors in the BM and alter the function of their terminally differentiated progeny.

Resident CD8 + and Migratory CD103 + Dendritic Cells Control CD8 T Cell Immunity during Acute Influenza Infection

The identification of the specific DC subsets providing a critical role in presenting influenza antigens to naïve T cell precursors remains contentious and under considerable debate. Here we show that CD8+ T lymphocyte (TCD8+) responses are severely hampered in C57BL/6 mice deficient in the transcription factor Batf3 after intranasal challenge with influenza A virus (IAV). This transcription factor is required for the development of lymph node resident CD8+ and migratory CD103+CD11b− DCs and we found both of these subtypes could efficiently stimulate anti-IAV TCD8+. Using a similar ex vivo approach, many publications on this subject matter excluded a role for resident, non-migratory CD8+ DC. We postulate the differences reported can partially be explained by how DC are phenotyped, namely the use of MHC class II to segregate subtypes. Our results show that resident CD8+ DC upregulate this marker during IAV infection and we advise against its use when isolating DC subtypes.

The Immune Response to Skin Trauma Is Dependent on the Etiology of Injury in a Mouse Model of Burn and Excision.

Skin trauma has many different causes including incision, blunt force, and burn. All of these traumas trigger an immune response. However, it is currently unclear whether the immune response is specific to the etiology of the injury. This study was established to determine whether the immune response to excision and burn injury of equivalent extent was the same. Using a mouse model of a full-thickness 19 mm diameter excision or 19 mm diameter full-thickness burn injury, we examined the innate immune response at the level of serum cytokine induction, whole-blood lymphocyte populations, dendritic cell function/phenotype, and the ensuing adaptive immune responses of CD4 and CD8 T-cell populations. Strikingly, both the innate and adaptive immune system responses differed between the burn and excision injuries. Acute cytokine induction was faster and different in profile to that of excision injury, leading to changes in systemic monocyte and neutrophil levels. Differences in the immune profile between burn and excision were also noted up to day 84 post injury, suggesting that the etiology of injury leads to sustained changes in the response. This may in part underlie clinical observations of differences in patient morbidity and mortality in response to different skin injury types.

Influenza A Infection Enhances Cross-Priming of CD8+ T Cells to Cell-Associated Antigens in a TLR7- and Type I IFN-Dependent Fashion

The initiation of antitumor immunity relies on dendritic cells (DCs) to cross-present cell-associated tumor Ag to CD8+ T cells (TCD8+) due to a lack of costimulatory molecules on tumor cells. Innate danger signals have been demonstrated to enhance cross-priming of TCD8+ to soluble as well as virally encoded Ags; however, their effect on enhancing TCD8+ cross-priming to cell genome-encoded Ags remains unknown. Furthermore, influenza A virus (IAV) has not been shown to enhance antitumor immunity. Using influenza-infected allogeneic cell lines, we show in this study that TCD8+ responses to cell-associated Ags can be dramatically enhanced due to enhanced TCD8+ expansion. This enhanced cross-priming in part involves TLR7- but not TLR3-mediated sensing of IAV and is entirely dependent on MyD88 and IFN signaling pathways. We also showed that the inflammasome-induced IL-1 and IFN-γ did not play a role in enhancing cross-priming in our system. We further demonstrated in our ex vivo system that CD8+ DCs are the only APCs able to prime TCR-transgenic TCD8+. Importantly, plasmacytoid DCs and CD8− DCs were both able to enhance such priming when provided in coculture. These observations suggest that IAV infection of tumor cells may facilitate improved cross-presentation of tumor Ags and may be used to augment clinical vaccine efficacy.

Dendritic cells and influenza A virus infection

Influenza A virus (IAV) is a dangerous virus equipped with the potential to evoke widespread pandemic disease. The 2009 H1N1 pandemic highlights the urgency for developing effective therapeutics against IAV infection. Vaccination is a major weapon to combat IAV and efforts to improve current regimes are critically important. Here, we will review the role of dendritic cells (DCs), a pivotal cell type in the initiation of robust IAV immunity. The complexity of DC subset heterogeneity in the respiratory tract and lymph node that drains the IAV infected lung will be discussed, together with the varied and in some cases, conflicting contributions of individual DC populations to presenting IAV associated antigen to T cells.

Prostaglandin E2 imprints a long-lasting effect on dendritic cell progenitors in the bone marrow

Dendritic cells (DCs) that differentiate in vitro from the bone marrow (BM) of mice with prostaglandin E2 (PGE2)‐associated inflammation of the skin, airways, or peritoneal cavity poorly initiate immune responses. To remove in vitro differentiation and allow BM‐derived DCs to seed the periphery under steady‐state conditions, as well as study the molecule proposed responsible, chimeric mice were engrafted for >16 wk with BM cells from mice exposed to PGE2. Serial PGE2‐chimeric mice were established with BM cells from the primary chimeric mice. Immune responses in the airways and skin of the PGE2‐chimeric mice and serial PGE2‐chimeric mice were significantly attenuated. After inflammatory challenges by intranasal LPS, topical fluorescein isothiocyanate, and intraperitoneal alum, DCs, macrophages, and neutrophils trafficked poorly in PGE2‐chimeric mice and serial PGE2‐chimeric mice. Injection of BM‐differentiated DCs from nonchimeric mice restored the reduced immune responses of PGE2‐chimeric mice. DCs from BM of 16‐wk‐engrafted PGE2‐chimeric and serial PGE2‐chimeric mice resembled cells differentiated from BM exposed to PGE2 for only 3 d, demonstrating the long‐lasting effect of PGE2 on DC progenitors. PGE2 attenuates systemic immune responses by modulating myeloid cell progenitors in the BM such that BM‐derived, terminally differentiated myeloid cells have poor trafficking ability to sites of need.

Tissue destruction caused by cytotoxic T lymphocytes induces deletional tolerance

Autoimmune diseases tend to be chronic and progressive, but how these responses are sustained is not clear. One cell type that might contribute to autoimmunity is the cytotoxic T lymphocyte (CTL), which, as a consequence of causing tissue destruction and production of cytokines, could provide a sustained supply of antigen and inflammatory signals for dendritic cells to maintain immune stimulation. Here we examined whether such CTL-mediated tissue damage alone could provide antigen in the right context to recruit immune effectors and sustain autoimmunity. We show that while CTL-mediated tissue damage caused the release of self-antigens that stimulated the proliferation of naive autoreactive CD8+ T cells, such responses failed to precipitate disease and, instead, led to deletional tolerance. These findings indicate that despite the capacity of CTLs to produce inflammatory cytokines and to cause tissue damage, their responses are not sustaining, but instead favor induction of self-tolerance.