Taichi Ezaki

Splenic outer periarterial lymphoid sheath (PALS): An immunoproliferative microenvironment constituted by antigen-laden marginal metallophils and ED2-positive macrophages in the rat

SummaryIn an attempt to reveal the role of antigen-laden marginal metallophil (MM) and other macrophages in the intrasplenic immune response of a specific B-cell lineage to a thymus-independent type-2 antigen (Ficoll conjugated with fluorescein isothiocyanate), simultaneous immuno-histological observations of the involved cells were performed in the rat. By newly established methods of double or triple immunostainings, time-kinetics of the following parameters were studied and compared: (1) the antigen, (2) the specific antibody-forming cells (AFC) directed to the fluorescein-isothiocyanate determinant, (3) proliferating cells labeled with 5-bromo-2′-deoxyuridine (BrdU), and (4) macrophage subpopulations recognized by monoclonal antibodies (ED2 and ED3). The antigen localized stably not only in the marginal-zone macrophages but also in the MM except around the follicular area. The increase of BrdU-positive cells was observed from day 2 up to day 4 after antigen injection mostly in the periphery of the periarterial lymphoid sheath (outer PALS), which indicated antigen-induced proliferation. As a novel finding, the majority of AFC, both BrdU-positive and -negative, were either closely associated with the antigen-laden MM, or forming cell clusters with ED2-positive macrophages in the outer PALS. In contrast, there were very few AFC in juxtaposition to antigen-free MM in the follicular area or the antigen-laden marginal zone macrophages. The results led to the proposal of a hypothesis that the antigen-laden MM together with ED2-positive macrophages constitute an immunoproliferative microenvironment for the plasmacellular reaction by accumulating the antigen-specific B-cell lineage and promoting these cells to differentiate into the AFC and to proliferate in the outer PALS.

Defective B1 cell homing to the peritoneal cavity and preferential recruitment of B1 cells in the target organs in a murine model for systemic lupus erythematosus.

We previously reported that B lymphocyte chemoattractant (BLC; CXCL13) was highly and ectopically expressed in aged (NZB × NZW)F1 (BWF1) mice developing lupus nephritis, and that B1 cells were preferentially chemoattracted toward BLC. We demonstrate in this study that B1 cells fail to home to the peritoneal cavity in aged BWF1 mice developing lupus nephritis, and that they are preferentially recruited to the target organs including the kidney, lung, and thymus when injected i.v. In contrast, B1 cells homed to the peritoneal cavity in aged BALB/c mice as effectively as in young mice. Accumulation of B1 cells to the omentum milky spots was also impaired in aged BWF1 mice compared with young mice. CD11bhighF4/80high cells with macrophage morphology were confirmed to be a major cell source for BLC in the peritoneal cavity both in young and aged BWF1 mice. However, the number of BLC-producing peritoneal macrophages was markedly decreased in aged BWF1 mice. These results suggest that the decreased number of BLC-producing peritoneal macrophages together with ectopic high expression of BLC in aged BWF1 mice result in abnormal B1 cell trafficking during the development of murine lupus.

Proliferating mesodermal cells in murine embryos exhibiting macrophage and lymphendothelial characteristics

BackgroundThe data on the embryonic origin of lymphatic endothelial cells (LECs) from either deep embryonic veins or mesenchymal (or circulating) lymphangioblasts presently available remain inconsistent. In various vertebrates, markers for LECs are first expressed in specific segments of embryonic veins arguing for a venous origin of lymph vessels. Very recently, studies on the mouse have strongly supported this view. However, in the chick, we have observed a dual origin of LECs from veins and from mesodermal lymphangioblasts. Additionally, in murine embryos we have detected mesenchymal cells that co-express LEC markers and the pan-leukocyte marker CD45. Here, we have characterized the mesoderm of murine embryos with LEC markers Prox1, Lyve-1 and LA102 in combination with macrophage markers CD11b and F4/80.ResultsWe observed cells co-expressing both types of markers (e.g. Prox1 – Lyve-1 – F4/80 triple-positive) located in the mesoderm, immediately adjacent to, and within lymph vessels. Our proliferation studies with Ki-67 antibodies showed high proliferative capacities of both the Lyve-1-positive LECs of lymph sacs/lymphatic sprouts and the Lyve-1-positive mesenchymal cells.ConclusionOur data argue for a dual origin of LECs in the mouse, although the primary source of embryonic LECs may reside in specific embryonic veins and mesenchymal lymphangioblasts integrated secondarily into lymph vessels. The impact of a dual source of LECs for ontogenetic, phylogenetic and pathological lymphangiogenesis is discussed.

Invariant NKT Cells Induce Plasmacytoid Dendritic Cell (DC) Cross-Talk with Conventional DCs for Efficient Memory CD8+ T Cell Induction

A key goal of vaccine immunotherapy is the generation of long-term memory CD8+ T cells capable of mediating immune surveillance. We discovered a novel intercellular pathway governing the development of potent memory CD8+ T cell responses against cell-associated Ags that is mediated through cross-presentation by XCR1+ dendritic cells (DCs). Generation of CD8+ memory T cells against tumor cells pulsed with an invariant NKT cell ligand depended on cross-talk between XCR1+ and plasmacytoid DCs that was regulated by IFN-α/IFN-αR signals. IFN-α production by plasmacytoid DCs was stimulated by an OX40 signal from the invariant NKT cells, as well as an HMGB1 signal from the dying tumor cells. These findings reveal a previously unknown pathway of intercellular collaboration for the generation of tumor-specific CD8+ memory T cells that can be exploited for strategic vaccination in the setting of tumor immunotherapy.

Renoprotective effects of an angiotensin II receptor blocker in experimental model rats with hypertension and metabolic disorders

Metabolic syndrome (MS) is an independent risk factor for chronic kidney diseases. As the renin–angiotensin system (RAS) is known to have a key role in renal damage, blockade of RAS may show renoprotective effects in MS. In this study, we investigated the renoprotective effects and mechanisms of action of an angiotensin receptor blocker (ARB) in spontaneously hypertensive (SHR/NDmcr-cp) rats as a model of MS. Male SHR/NDmcr-cp rats at 9 weeks of age were divided into three groups, each of which was treated for 12 weeks with vehicle, hydralazine (7.5u2009mgu2009kg−1 per day, p.o.) or ARB (olmesartan, 5u2009mgu2009kg−1 per day, p.o.). Blood pressure and urinary protein (UP) excretion were monitored. Kidney tissues were subjected to histological, immunohistochemical and molecular analyses. UP excretion increased with age in vehicle-treated SHR/NDmcr-cp rats compared with that in age-matched WKY/Izm rats. In addition, there was significant glomerular damage (increased glomerular sclerosis index, desmin staining and proliferating cell nuclear antigen (PCNA)-positive cells, electron microscopic findings of podocyte injury) and tubulointerstitial damage (increased tubulointerstitial fibrosis index, type IV collagen staining, PCNA-positive cells and expression of TGF-β mRNA) in vehicle-treated SHR/NDmcr-cp rats compared with that in control rats. All the findings that related to glomerular and tubulointerstitial damage were significantly improved by ARB. Hydralazine mitigated the observed renal damage but was much less effective than ARB, despite similar decreases in blood pressure. There were no significant differences in glucose and lipid metabolism among vehicle-treated, hydralazine-treated and ARB-treated SHR/NDmcr-cp animals. These data suggest that RAS is deeply involved in the pathogenesis of renal damage in MS, and ARBs could provide a powerful renoprotective regimen for patients with MS.

Characterization of sinusoidal endothelial cells of the liver and bone marrow using an intravital lectin injection method

The vascular endothelia express a variety of structural and biological phenotypes. We used an intravital injection method of plant derived lectins (Lycopersicon esculentum lectin (LEL), Ricinus communis Agglutinin-I (RCA-I), Ulex europaeus Agglutinin-I (UEA-I) and Concanavalin A (ConA)) to elucidate the morphology and function of the sinusoidal endothelium of the liver and bone marrow. All four lectins stained the sinusoidal endothelia of the liver and bone marrow in a patchy granular pattern which differed from the uniform and smooth staining pattern of non-sinusoidal vessels in other organs. By transmission electron microscopy, the granular pattern was identified as internalization of these lectins and subsequent accumulation within the endothelial cells, suggesting their active endocytosis. The endocytosis of these lectins emphasizes the fact that sinusoidal endothelial cells of the liver and bone marrow belong to the reticuloendothelial system (RES), a cell system characterized by internalization of foreign material. We introduce this intravital lectin injection as a useful technique to discriminate sinusoidal endothelial of the liver and bone marrow from other vascular endothelia.

Targeting of tumor endothelial cells combining 2 Gy/day of X-ray with Everolimus is the effective modality for overcoming clinically relevant radioresistant tumors.

Radiotherapy is widely used to treat cancer because it has the advantage of physically and functionally conserving the affected organ. To improve radiotherapy and investigate the molecular mechanisms of cellular radioresistance, we established a clinically relevant radioresistant (CRR) cell line, SAS‐R, from SAS cells. SAS‐R cells continue to proliferate when exposed to fractionated radiation (FR) of 2 Gy/day for more than 30 days in vitro. A xenograft tumor model of SAS‐R was also resistant to 2 Gy/day of X‐rays for 30 days. The density of blood vessels in SAS‐R tumors was higher than in SAS tumors. Everolimus, a mammalian target of rapamycin (mTOR) inhibitor, sensitized microvascular endothelial cells to radiation, but failed to radiosensitize SAS and SAS‐R cells in vitro. Everolimus with FR markedly reduced SAS and SAS‐R tumor volumes. Additionally, the apoptosis of endothelial cells (ECs) increased in SAS‐R tumor tissues when both Everolimus and radiation were administered. Both CD34‐positive and tomato lectin‐positive blood vessel densities in SAS‐R tumor tissues decreased remarkably after the Everolimus and radiation treatment. Everolimus‐induced apoptosis of vascular ECs in response to radiation was also followed by thrombus formation that leads to tumor necrosis. We conclude that FR combined with Everolimus may be an effective modality to overcome radioresistant tumors via targeting tumor ECs.

The Liver Sinusoids as a Specialized Site for Blood-Lymph Translocation of Rat Dendritic Cells

The fate as well as the significance of blood dendritic cells (DC) is not yet completely resolved. Some may migrate to the splenic white pulp1 and other immature DC may reach the epithelial tissues to become resident DC. When particulates are injected intravenously, relatively immature particle-laden DC appear in the peripheral lymph draining the liver2. The results suggest that the rat DC lineage may be selectively recruited to the liver after intravenous injection of particulates and that they subsequently translocate from the liver vasculature to the hepatic lymph. The present study was performed to demonstrate the migration pathway of blood DC and the existence of specialized vasculature for DC, the liver sinusoids.

Local lymphogenic migration pathway in normal mouse spleen

Although the immunological and hemodynamical significance of the spleen is of great importance, few reports detail the lymphatic vessels in this organ. We have used an immunohistochemical three-dimensional imaging technique to characterize lymphatic vessels in the normal mouse spleen and have successfully demonstrated their spatial relationship to the blood vascular system for the first time. Lymphatic markers, such as LYVE-1, VEGFR-3, and podoplanin, show different staining patterns depending on their location in the spleen. LYVE-1-positive lymphatic vessels run reverse to the arterial blood flow along the central arteries in the white pulp and trabecular arteries and exit the spleen from the hilum. These lymphatic vessels are surrounded by type IV collagen, indicating that they are collecting lymphatic vessels rather than lymphatic capillaries. Podoplanin is expressed not only in lymphatic vessels, but also in stromal cells in the white pulp. These podoplanin-positive cells form fine meshworks surrounding the lymphatic vessels and central arteries. Following intravenous transplantation of lymphocytes positive for green fluorescent protein (GFP+) into normal recipient mice, donor cells appear in the meshworks within 1 h and accumulate in the lymphatic vessels within 6 h after injection. The GFP+ cells further accumulate in a draining celiac lymph node through the efferent lymphatic vessels from the hilum. These meshworks might therefore act as an extravascular lymphatic pathway and, together with ordinary lymphatic vessels, play a primary role in the cell traffic of the spleen, additional to the blood circulatory system.

Alteration of angiogenic patterns on B16BL6 melanoma development promoted in Matrigel

Because the progression and metastasis of solid tumors depend on their local microcirculation, we sought to characterize tumor angiogenesis three dimensionally in a highly metastatic mouse melanoma model, B16BL6 (B16), injected with Matrigel into the subcutis in the skin on the back of syngeneic C57BL/6 mice. We found that B16 with Matrigel grew significantly faster than B16 alone and had altered tumor angiogenesis. Tumor vessels apparently grew vigorously in the opposite direction of the tumor without invading the tumor mass until at least day 10 of injection. In addition, vascular branching resulted not only from sprouting as was seen in B16 without Matrigel but also from vascular splitting, either because of compression from outside the vessels or from septum formation by endothelial cells. This phenomenon was characteristic of B16 cells, but not of other tumor cells, including Lewis lung carcinoma and ASH-1 hybridoma cell lines, both of which were tested under the same conditions. The reduction in various angiogenic factors in Matrigel did not affect the angiogenic patterns and tumor growth. We hypothesize that tumor vessels may vigorously alter their angiogenic patterns in response to the local microenvironment.