Induction of histiocytic sarcoma in mouse skeletal muscle

Myeloid sarcomas are extramedullary accumulations of immature myeloid cells that may present with or without evidence of pathologic involvement of the bone marrow or peripheral blood, and often coincide with or precede a diagnosis of acute myeloid leukemia (AML). A dearth of experimental models has hampered the study of myeloid sarcomas and led us to establish a new system in which tumor induction can be evaluated in an easily accessible non-hematopoietic tissue compartment. Using ex-vivo transduction of oncogenic Kras(G12V) into p16/p19(-/-) bone marrow cells, we generated transplantable leukemia-initiating cells that rapidly induced tumor formation in the skeletal muscle of immunocompromised NOD.SCID mice. In this model, murine histiocytic sarcomas, equivalent to human myeloid sarcomas, emerged at the injection site 30-50 days after cell implantation and consisted of tightly packed monotypic cells that were CD48+, CD47+ and Mac1+, with low or absent expression of other hematopoietic lineage markers. Tumor cells also infiltrated the bone marrow, spleen and other non-hematopoietic organs of tumor-bearing animals, leading to systemic illness (leukemia) within two weeks of tumor detection. P16/p19(-/-); Kras(G12V) myeloid sarcomas were multi-clonal, with dominant clones selected during secondary transplantation. The systemic leukemic phenotypes exhibited by histiocytic sarcoma-bearing mice were nearly identical to those of animals in which leukemia was introduced by intravenous transplantation of the same donor cells. Moreover, murine histiocytic sarcoma could be similarly induced by intramuscular injection of MLL-AF9 leukemia cells. This study establishes a novel, transplantable model of murine histiocytic/myeloid sarcoma that recapitulates the natural progression of these malignancies to systemic disease and indicates a cell autonomous leukemogenic mechanism.     

Transforming growth factor beta: possible roles in the regulation of normal and leukemic hematopoietic cell growth

We have recently demonstrated that transforming growth factor (TGF)-beta 1 and TGF-beta 2 are potent inhibitors of the growth and differentiation of murine and human hematopoietic cells. The proliferation of primary unfractionated murine bone marrow by interleukin-3 (IL-3) and human bone marrow by IL-3 or granulocyte/macrophage colony-stimulating factor (GM-CSF) was inhibited by TGF-beta 1 and TGF-beta 2, while the proliferation of murine bone marrow by GM-CSF or murine and human marrow with G-CSF was not inhibited. Mouse and human hematopoietic colony formation was differentially affected by TGF-beta 1. In particular, CFU-GM, CFU-GEMM, BFU-E, and HPP-CFC, the most immature colonies, were inhibited by TGF-beta 1, whereas the more differentiated unipotent CFU-G, CFU-M, and CFU-E were not affected. TGF-beta 1 inhibited IL-3-induced growth of murine leukemic cell lines within 24 h, after which the cells were still viable. Subsequent removal of the TGF-beta 1 results in the resumption of normal growth. TGF-beta 1 inhibited the growth of factor-dependent NFS-60 cells in a dose-dependent manner in response to IL-3, GM-CSF, G-CSF, CSF-1, IL-4, or IL-6. TGF-beta 1 inhibited the growth of a variety of murine and human myeloid leukemias, while erythroid and macrophage leukemias were insensitive. Lymphoid leukemias, whose normal cellular counterparts were markedly inhibited by TGF-beta, were also resistant to TGF-beta 1 inhibition. These leukemic cells have no detectable TGF-beta 1 receptors on their cell surface. Last, TGF-beta 1 directly inhibited the growth of isolated Thy-1-positive progenitor cells. Thus, TGF-beta may be an important modulator of normal and leukemic hematopoietic cell growth.     

Notch1 perturbation of hemopoiesis involves non-cell- autonomous modifications

To study the effects of Notch on hemopoiesis we used a bone marrow transduction/transplantation model and compared the transduced and nontransduced populations in reconstituted mice. While cells expressing a constitutively active form of murine Notch1 (Notch1IC) completely lacked B cells, a profound suppression of the B lineage was also seen in the nontransduced compartment. Experiments performed with retroviral supernatants of varying titers showed that the perturbations of B cell development among the nontransduced population correlated with the percentage of Notch1IC-transduced cells inoculated into the mice. The myeloid lineage of the Notch1IC-transplanted mice was altered as well, and this also affected the nontransduced population that had features of excessive maturation. To explore the basis of these non-cell-autonomous modifications we prepared conditioned medium from ex vivo cultures of Notch1IC-transplanted mice bone marrow and showed that it inhibited B cell maturation and promoted myeloid differentiation in a dose-dependent manner. Finally, we found that the T cell leukemia/lymphomas that occur in Notch1IC-transplanted mice were accompanied by abnormal maturation of nontransduced T cells in the bone marrow. These findings indicate that modifications of neighboring cells through non-cell-autonomous modifications take part in multiple facets of the activity of Notch on hemopoiesis.     

IL-15 can signal via IL-15Rα, JNK, and NF-κB to drive RANTES production by myeloid cells

IL-15 plays many important roles within the immune system. IL-15 signals in lymphocytes via trans presentation, where accessory cells such as macrophages and dendritic cells present IL-15 bound to IL-15Rα in trans to NK cells and CD8(+) memory T cells expressing IL-15/IL-2Rβ and common γ chain (γ(c)). Previously, we showed that the prophylactic delivery of IL-15 to Rag2(-/-)γ(c)(-/-) mice (mature T, B, and NK cell negative) afforded protection against a lethal HSV-2 challenge and metastasis of B16/F10 melanoma cells. In this study, we demonstrated that in vivo delivery of an adenoviral construct optimized for the secretion of human IL-15 to Rag2(-/-)γ(c)(-/-) mice resulted in significant increases in spleen size and cell number, leading us to hypothesize that IL-15 signals differently in myeloid immune cells compared with lymphocytes, for which IL-15/IL-2Rβ and γ(c) expression are essential. Furthermore, treatment with IL-15 induced RANTES production by Rag2(-/-)γ(c)(-/-) bone marrow cells, but the presence of γ(c) did not increase bone marrow cell sensitivity to IL-15. This IL-15-mediated RANTES production by Rag2(-/-)γ(c)(-/-) bone marrow cells occurred independently of the IL-15/IL-2Rβ and Jak/STAT pathways and instead required IL-15Rα signaling as well as activation of JNK and NF-κB. Importantly, we also showed that the trans presentation of IL-15 by IL-15Rα boosts IL-15-mediated IFN-γ production by NK cells but reduces IL-15-mediated RANTES production by Rag2(-/-)γ(c)(-/-) myeloid bone marrow cells. Our data clearly show that IL-15 signaling in NK cells is different from that of myeloid immune cells. Additional insights into IL-15 biology may lead to novel therapies aimed at bolstering targeted immune responses against cancer and infectious disease.     

Induced SHIP deficiency expands myeloid regulatory cells and abrogates graft-versus-host disease

Graft-vs-host disease (GVHD) is the leading cause of treatment-related death in allogeneic bone marrow (BM) transplantation. Immunosuppressive strategies to control GVHD are only partially effective and often lead to life-threatening infections. We previously showed that engraftment of MHC-mismatched BM is enhanced and GVHD abrogated in recipients homozygous for a germline SHIP mutation. In this study, we report the development of a genetic model in which SHIP deficiency can be induced in adult mice. Using this model, we show that the induction of SHIP deficiency in adult mice leads to a rapid and significant expansion of myeloid suppressor cells in peripheral lymphoid tissues. Consistent with expansion of myeloid suppressor cells, splenocytes and lymph node cells from adult mice with induced SHIP deficiency are significantly compromised in their ability to prime allogeneic T cell responses. These results demonstrate that SHIP regulates homeostatic signals for these immunoregulatory cells in adult physiology. Consistent with these findings, induction of SHIP deficiency before receiving a T cell-replete BM graft abrogates acute GVHD. These findings indicate strategies that target SHIP could increase the efficacy and utility of allogeneic BM transplantation, and thereby provide a curative therapy for a wide spectrum of human diseases.     

Extracellular matrix proteoglycans control the fate of bone marrow stromal cells

Extracellular matrix glycoproteins and proteoglycans bind a variety of growth factors and cytokines thereby regulating matrix assembly as well as bone formation. However, little is known about the mechanisms by which extracellular matrix molecules modulate osteogenic stem cells and bone formation. Using mice deficient in two members of the small leucine-rich proteoglycans, biglycan and decorin, we uncovered a role for these two extracellular matrix proteoglycans in modulating bone formation from bone marrow stromal cells. Our studies showed that the absence of the critical transforming growth factor-beta (TGF-beta)-binding proteoglycans, biglycan and decorin, prevents TGF-beta from proper sequestration within the extracellular matrix. The excess TGF-beta directly binds to its receptors on bone marrow stromal cells and overactivates its signaling transduction pathway. Overall, the predominant effect of the increased TGF-beta signaling in bgn/dcn-deficient bone marrow stromal cells is a "switch in fate" from growth to apoptosis, leading to decreased numbers of osteoprogenitor cells and subsequently reduced bone formation. Thus, biglycan and decorin appear to be essential for maintaining an appropriate number of mature osteoblasts by modulating the proliferation and survival of bone marrow stromal cells. These findings underscore the importance of the micro-environment in controlling the fate of adult stem cells and reveal a novel cellular and molecular basis for the physiological and pathological control of bone mass.     

Signaling pathways involved in MDSC regulation

The immune system has evolved mechanisms to protect the host from the deleterious effects of inflammation. The generation of immune suppressive cells like myeloid derived suppressor cells (MDSCs) that can counteract T cell responses represents one such strategy. There is an accumulation of immature myeloid cells or MDSCs in bone marrow (BM) and lymphoid organs under pathological conditions such as cancer. MDSCs represent a population of heterogeneous myeloid cells comprising of macrophages, granulocytes and dendritic cells that are at early stages of development. Although, the precise signaling pathways and molecular mechanisms that lead to MDSC generation and expansion in cancer remains to be elucidated. It is widely believed that perturbation of signaling pathways involved during normal hematopoietic and myeloid development under pathological conditions such as tumorogenesis contributes to the development of suppressive myeloid cells. In this review we discuss the role played by key signaling pathways such as PI3K, Ras, Jak/Stat and TGFb during myeloid development and how their deregulation under pathological conditions can lead to the generation of suppressive myeloid cells or MDSCs. Targeting these pathways should help in elucidating mechanisms that lead to the expansion of MDSCs in cancer and point to methods for eliminating these cells from the tumor microenvironment.     

Adaptive and innate transforming growth factor beta signaling impact herpes simplex virus 1 latency and reactivation

Innate and adaptive immunity play important protective roles by combating herpes simplex virus 1 (HSV-1) infection. Transforming growth factor β (TGF-β) is a key negative cytokine regulator of both innate and adaptive immune responses. Yet, it is unknown whether TGF-β signaling in either immune compartment impacts HSV-1 replication and latency. We undertook genetic approaches to address these issues by infecting two different dominant negative TGF-β receptor type II transgenic mouse lines. These mice have specific TGF-β signaling blockades in either T cells or innate cells. Mice were ocularly infected with HSV-1 to evaluate the effects of restricted innate or adaptive TGF-β signaling during acute and latent infections. Limiting innate cell but not T cell TGF-β signaling reduced virus replication in the eyes of infected mice. On the other hand, blocking TGF-β signaling in either innate cells or T cells resulted in decreased latency in the trigeminal ganglia of infected mice. Furthermore, inhibiting TGF-β signaling in T cells reduced cell lysis and leukocyte infiltration in corneas and trigeminal ganglia during primary HSV-1 infection of mice. These findings strongly suggest that TGF-β signaling, which generally functions to dampen immune responses, results in increased HSV-1 latency.     

IL-23 is critical for induction of arthritis, osteoclast formation, and maintenance of bone mass

The role of IL-23 in the development of arthritis and bone metabolism was studied using systemic IL-23 exposure in adult mice via hydrodynamic delivery of IL-23 minicircle DNA in vivo and in mice genetically deficient in IL-23. Systemic IL-23 exposure induced chronic arthritis, severe bone loss, and myelopoiesis in the bone marrow and spleen, which resulted in increased osteoclast differentiation and systemic bone loss. The effect of IL-23 was partly dependent on CD4(+) T cells, IL-17A, and TNF, but could not be reproduced by overexpression of IL-17A in vivo. A key role in the IL-23-induced arthritis was made by the expansion and activity of myeloid cells. Bone marrow macrophages derived from IL-23p19(-/-) mice showed a slower maturation into osteoclasts with reduced tartrate-resistant acid phosphatase-positive cells and dentine resorption capacity in in vitro osteoclastogenesis assays. This correlated with fewer multinucleated osteoclast-like cells and more trabecular bone volume and number in 26-wk-old male IL-23p19(-/-) mice compared with control animals. Collectively, our data suggest that systemic IL-23 exposure induces the expansion of a myeloid lineage osteoclast precursor, and targeting IL-23 pathway may combat inflammation-driven bone destruction as observed in rheumatoid arthritis and other autoimmune arthritides.     

Myeloid-specific expression of human lysosomal acid lipase corrects malformation and malfunction of myeloid-derived suppressor cells in lal-/- mice

Lysosomal acid lipase (LAL) cleaves cholesteryl esters and triglycerides to generate free fatty acids and cholesterol in lysosomes. LAL deficiency causes expansion of CD11b(+)Gr-1(+) immature myeloid cells, loss of T cells, and impairment of T cell function. To test how myeloid cell LAL controls myelopoiesis and lymphopoiesis, a myeloid-specific doxycycline-inducible transgenic system was used to reintroduce human lysosomal acid lipase (hLAL) expression into LAL gene knockout (lal(-/-)) mice. Expression of hLAL in myeloid cells of lal(-/-) mice reversed abnormal myelopoiesis in the bone marrow starting at the granulocyte-monocyte progenitor stage and reduced systemic expansion of myeloid-derived suppressor cells (MDSCs). Myeloid hLAL expression inhibited reactive oxygen species production and arginase expression in CD11b(+)Gr-1(+) cells of lal(-/-) mice. Structural organization of the thymus and spleen was partially restored in association with reduced infiltration of CD11b(+)Gr-1(+) cells in these mice. In the thymus, reconstitution of myeloid cell LAL restored development of thymocytes at the double-negative DN3 stage. Myeloid cell LAL expression improved the proliferation and function of peripheral T cells. In vitro coculture experiments showed that myeloid hLAL expression in lal(-/-) mice reversed CD11b(+)Gr-1(+) myeloid cell suppression of CD4(+) T cell proliferation, T cell signaling activation, and lymphokine secretion. Blocking stat3 and NF-κB p65 signaling by small-molecule inhibitors in MDSCs achieved a similar effect. Injection of anti-Gr-1 Ab into lal(-/-) mice to deplete MDSCs restored T cell proliferation. These studies demonstrate that LAL in myeloid cells plays a critical role in maintaining normal hematopoietic cell development and balancing immunosuppression and inflammation.     

Alcohol suppresses the granulopoietic response to pulmonary Streptococcus pneumoniae infection with enhancement of STAT3 signaling

Enhanced granulopoietic activity is crucial for host defense against bacterial pneumonia. Alcohol impairs this response. The underlying mechanisms remain obscure. G-CSF produced by infected lung tissue plays a key role in stimulating bone marrow granulopoiesis. This study investigated the effects of alcohol on G-CSF signaling in the regulation of marrow myeloid progenitor cell proliferation in mice with Streptococcus pneumoniae pneumonia. Chronic alcohol consumption plus acute alcohol intoxication suppressed the increase in blood granulocyte counts following intrapulmonary challenge with S. pneumoniae. This suppression was associated with a significant decrease in bone marrow granulopoietic progenitor cell proliferation. Alcohol treatment significantly enhanced STAT3 phosphorylation in bone marrow cells of animals challenged with S. pneumoniae. In vitro experiments showed that G-CSF-induced activation of STAT3-p27(Kip1) pathway in murine myeloid progenitor cell line 32D-G-CSFR cells was markedly enhanced by alcohol exposure. Alcohol dose dependently inhibited G-CSF-stimulated 32D-G-CSFR cell proliferation. This impairment of myeloid progenitor cell proliferation was not attenuated by inhibition of alcohol metabolism through either the alcohol dehydrogenase pathway or the cytochrome P450 system. These data suggest that alcohol enhances G-CSF-associated STAT3-p27(Kip1) signaling, which impairs granulopoietic progenitor cell proliferation by inducing cell cycling arrest and facilitating their terminal differentiation during the granulopoietic response to pulmonary infection.     

Cutting edge: TGF-beta signaling is required for the in vivo expansion and immunosuppressive capacity of regulatory CD4+CD25+ T cells

Data regarding the role of TGF-beta for the in vivo function of regulatory CD4(+)CD25(+) T cells (Treg) are controversial. A transgenic mouse model with impaired TGF-beta signaling specifically in T cells was used to assess the role of endogenous TGF-beta for the in vivo function of CD4(+)CD25(+) Treg in a murine model of colitis induced by dextran sulfate. Transfer of wild-type, but not transgenic CD4(+)CD25(+) Treg was found to suppress colitis in wild-type mice. In addition, by transferring CFSE-labeled CD4(+)CD25(+) Treg we could demonstrate that endogenous TGF-beta promotes the expansion of CD4(+)CD25(+) Treg in vivo. Transgenic mice themselves developed reduced numbers of peripheral CD4(+)CD25(+) Treg and were more susceptible to the induction of colitis, which could be prevented by the transfer of wild-type Treg. These data indicate that TGF-beta signaling in CD4(+)CD25(+) Treg is required for their in vivo expansion and suppressive capacity.     

Function of the IL-2R for thymic and peripheral CD4+CD25+ Foxp3+ T regulatory cells

IL-2 contributes to the production, function, and homeostasis of CD4+CD25+ T(reg) cells. However, it remains uncertain whether IL-2 is essential for the development of T(reg) cells in the thymus, their homeostasis in the periphery, or both. The present study was undertaken to investigate the contribution of IL-2 during thymic T(reg) cell development and its maintenance in peripheral immune tissue. Relying on genetic mouse models where IL-2R signaling was either completely blocked or selectively inhibited in peripheral CD4+CD25+ T(reg) cells, we show that the IL-2/IL-2R interaction is active in the thymus at the earliest stage of the development of T(reg) cells to promote their expansion and to up-regulate Foxp3 and CD25 to normal levels. Furthermore, CD4+CD25+Foxp3+ T(reg) cells with impaired IL-2-induced signaling persist in the periphery and control autoimmunity without constant thymic output. These peripheral T(reg) cells with poor responsiveness to IL-2 exhibited slower growth and extended survival in vivo, somewhat lower suppressive activity, and poor IL-2-dependent survival in vitro. Mixed thymic and bone marrow chimeric mice showed that wild-type-derived T(reg) cells were substantially more effective in populating peripheral immune tissue than T(reg) cells with impaired IL-2 signaling. Collectively, these data support the notion that normally IL-2 is a dominant mechanism controlling the number of thymic and peripheral T(reg) cells.     

In vivo overexpression of Core2 N-Acetylglucosaminyltransferase prevents repopulation of the bone marrow with colony forming cells but fails to affect normal T cell development

UDP-GlcNAc:Galβ1 → 3GalNAc-R β1 → 6N-acetylglucosaminyltransferase (Core2 N-acetyl-glucosaminyltransferase, C2GnT; EC 2.4.1.102) forms β1 → 6N-acetyl-glucosaminyl linkages in O-glycoproteins and creates branches for the addition of N-acetyl-lactosamine antennae. Changes in C2GnT activity have been associated with immune disorders, malignancies, and T-cell ontogeny. In this study, we used SCID (severe combined immune deficiency) mice to determine the effects of C2GnT overexpression on hemopoiesis, and in particular, on thymocyte development. BALB/c bone marrow cells transfected with C2GnT using the retroviral murine stem cell vector were used to repopulate SCID mice. Mice were analysed 3 weeks to 3 months after bone marrow transfer. Elevated levels of C2GnT activity in bone marrow, spleen, and thymus from mice repopulated with C2GnT transfected bone marrow cells indicated that C2GnT was overexpressed in recipient mice. In C2GnT repopulated mice, up to 50% of T cells showed an increase in CD43 130-kDa expression, compared with T cells from control animals, indicative of an elevated C2GnT activity in these cells. Furthermore, T-cell subset numbers appeared to be normal, suggesting that C2GnT overexpression did not alter T-cell ontogeny. Interestingly, C2GnT overexpression negatively affected the repopulation of myeloid cells. Only insignificant numbers of interleukin-3/granulocyte-macrophage colony stimulating factor (IL-3/GM-CSF) responsive bone marrow cells were found to be retrovirally transfected in C2GnT repopulated mice, whereas up to 50% of IL-3/GM-CSF responsive bone marrow cells were found to be retrovirally transfected in corresponding controls. These data indicate that in vivo overexpression of C2GnT negatively interferes with the myeloid differentiation pathway but does not affect T-cell development. J. Cell. Physiol. 176:350–358, 1998. © 1998 Wiley-Liss, Inc.     

Distribution of cycling T lymphocytes in blood and lymphoid organs during immune responses

Proliferation of murine T lymphocytes in blood, lymph nodes, and spleen was studied in four in vivo stimulation systems, using BrdU pulse-labeling of DNA-synthesizing cells. The T cell response to the superantigen Staphylococcus enterotoxin B (SEB) was studied in detail. Vbeta8+ T cells showed a peak of DNA synthesis 16-24 h after SEB injection, and the percentage of BrdU+ CD4 and CD8 T cells was higher in blood than in lymph nodes and spleen. DNA synthesis was preceded by massive migration of Vbeta8+ cells from blood to lymphoid organs, in which the early activation marker CD69 was first up-regulated. SEB-nonspecific Vbeta6+ cells showed minimal stimulation but, when cycling, also expressed a high level of CD69. The other systems studied were injection of the IFN-gamma inducer polyinosinic:polycytidylic acid, infection by the BM5 variants of murine leukemia virus (the causative agent of murine AIDS), and T cell expansion after transfer of normal bone marrow and lymph node cells into recombinase-activating gene-2-deficient mice. In each case, a peak of T cell proliferation was observed in blood. These data demonstrate the extensive redistribution of cycling T cells in the first few hours after activation. Kinetic studies of blood lymphocyte status appear crucial for understanding primary immune responses because cycling and redistributing T lymphocytes are enriched in the circulating compartment.     

The interplay of osteogenesis and hematopoiesis: expression of a constitutively active PTH/PTHrP receptor in osteogenic cells perturbs the establishment of hematopoiesis in bone and of skeletal stem cells in the bone marrow

The ontogeny of bone marrow and its stromal compartment, which is generated from skeletal stem/progenitor cells, was investigated in vivo and ex vivo in mice expressing constitutively active parathyroid hormone/parathyroid hormone-related peptide receptor (PTH/PTHrP; caPPR) under the control of the 2.3-kb bone-specific mouse Col1A1 promoter/enhancer. The transgene promoted increased bone formation within prospective marrow space, but delayed the transition from bone to bone marrow during growth, the formation of marrow cavities, and the appearance of stromal cell types such as marrow adipocytes and cells supporting hematopoiesis. This phenotype resolved spontaneously over time, leading to the establishment of marrow containing a greatly reduced number of clonogenic stromal cells. Proliferative osteoprogenitors, but not multipotent skeletal stem cells (mesenchymal stem cells), capable of generating a complete heterotopic bone organ upon in vivo transplantation were assayable in the bone marrow of caPPR mice. Thus, PTH/PTHrP signaling is a major regulator of the ontogeny of the bone marrow and its stromal tissue, and of the skeletal stem cell compartment.     

TLR2 signaling and Th2 responses drive Tannerella forsythia-induced periodontal bone loss

Periodontal disease (PD) is a chronic inflammation of the tooth-supporting soft tissue and alveolar bone due to infection by a select group of gram-negative microbes, which leads to tooth loss if untreated. Because mice deficient in CD4(+) cells are resistant to infection-induced alveolar bone loss, Th cells have been implicated in bone-destructive processes during PD. However, the extent to which different Th cell subtypes play roles in pathogenesis or host protection remains to be defined and is likely to vary depending on the dominant microorganism involved. By far, Porphyromonas gingivalis is the best-studied periodontal microbe in PD. Although the gram-negative anaerobe Tannerella forsythia is also a vital contributor to periodontal bone loss, almost nothing is known about immune responses to this organism. Previous studies from our laboratory revealed that T. forsythia induces periodontal bone loss in mice and that this bone loss depends on the bacterially expressed BspA protein. In this study, we showed that T. forsythia activates murine APCs primarily through TLR2-dependent signaling via BspA. Furthermore, T. forsythia infection causes a pronounced Th2 bias, evidenced by T cell expression of IL-5, but not IFN-γ or IL-17, in draining lymph nodes. Consistently, deficiencies in TLR2 or STAT6 result in resistance to T. forsythia-induced alveolar bone loss. Thus, TLR2 signaling and Th2 cells play pathogenic roles in T. forsythia-induced alveolar bone destruction.     

Anatomical and cellular requirements for the activation and migration of virus-specific CD8+ T cells to the brain during Theiler's virus infection

Theiler's murine encephalomyelitis virus (TMEV) infection of the brain induces a virus-specific CD8(+) T-cell response in genetically resistant mice. The peak of the immune response to the virus occurs 7 days after infection, with an immunodominant CD8(+) T-cell response against a VP2-derived capsid peptide in the context of the D(b) molecule. The process of activation of antigen-specific T cells that migrate to the brain in the TMEV model has not been defined. The site of antigenic challenge in the TMEV model is directly into the brain parenchyma, a site that is considered immune privileged. We investigated the hypothesis that antiviral CD8(+) T-cell responses are initiated in situ upon intracranial inoculation with TMEV. To determine whether a brain parenchymal antigen-presenting cell is responsible for the activation of virus-specific CD8(+) T cells, we evaluated the CD8(+) T-cell response to the VP2 peptide in bone marrow chimeras and mutant mice lacking peripheral lymphoid organs. The generation of the anti-TMEV CD8(+) T-cell response in the brain requires priming by a bone marrow-derived antigen-presenting cell and the presence of peripheral lymphoid organs. Although our results show that activation of TMEV-specific CD8(+) T cells occurs in the peripheral lymphoid compartment, they do not exclude the possibility that the immune response to TMEV is initiated by a brain-resident, bone marrow-derived, antigen-presenting cell.