Histamine deficiency inhibits lymphocyte infiltration in the submandibular gland of aged mice via increased anti-aging factor Klotho.

OBJECTIVES: Histidine decarboxylase (HDC), a histamine synthase, is expressed in various tissues and is induced by proinflammatory cytokines such as TNFα. As they age, C57BL/6 mice show auto-antibody deposition and lymphocyte infiltration into various tissues, including salivary glands. However, the mechanism underlying cell infiltration and the change in HDC expression in salivary glands with aging remain unclear. Thus, we aimed to elucidate the relationship between histamine and inflammaging. METHODS: We investigated the change in histology and HDC expression in the major salivary glands (parotid, submandibular, and sublingual) of 6-week- and 9-month-old wild-type mice. We also determined the histological changes, cytokine expression, and anti-aging factor Klotho in the salivary glands of 9-month-old wild-type and HDC-deficient (HDC-KO) mice. RESULTS: Cell infiltration was observed in the submandibular gland of 9-month-old wild-type mice. Although most cells infiltrating the submandibular glands were CD3-positive and B220-positive lymphocytes, CD11c-positive and F4/80-positive monocyte lineages were also detected. HDC, TNFα, and IL-1ß mRNA expression increased in the submandibular gland of 9-month-old wild-type mice. The expression of PPARγ, an anti-inflammatory protein, declined in 9-month-old wild-type mice, and Klotho expression increased in 9-month-old HDC-KO mice. Immunohistochemistry showed that Klotho-positive cells disappeared in the submandibular gland of 9-month-old wild-type mice, while Klotho was detected in all salivary glands in HDC-KO mice of the same age. CONCLUSION: Our findings demonstrate the multifunctionality of histamine and can aid in the development of novel therapeutic methods for inflammatory diseases such as Sjogren's syndrome and age-related dysfunctions.

Expression of type VI collagen α3 chain in canine mammary carcinomas.

This study aimed to investigate the expression of type VI collagen α3 chain (COL6a3) in neoplastic cells of canine mammary gland carcinomas (CMGCs) using immunohistochemistry (IHC) and to evaluate the association between COL6a3 expression and tumor histological features, histological grades, and the differentiation status of neoplastic epithelial cells. COL6a3 expression in carcinoma cells was significantly associated with histologically low malignancy and low mitotic indices. In addition, COL6a3+ carcinoma cells were more frequently detected in simple carcinomas (tubular and tubulopapillary types) than in solid carcinomas. These findings indicate that reduced expression of COL6a3 in carcinoma cells contributes to the malignant phenotype in CMGCs. We also showed that COL6a3 expression in the carcinoma cells was more frequently detected in CK19+/CD49f + and/or CK19+/CK5+ tumors. In addition, COL6a3+/CK19+/CD49f + and COL6a3+/CK19+/CK5+ tumors consisted of CK19+/CD49f + and CK19+/CD49f- cells, and CK19+/CK5+ and CK19+/CK5- cells, respectively. Most of these tumors more frequently expressed GATA3, but not Notch1. These results indicate that COL6a3 is expressed in CMGCs containing both luminal progenitor-like and mature luminal-like cells and showing differentiation ability into mature luminal cells. It is possible that COL6 may be involved in the differentiation of luminal progenitor-like carcinoma cells into mature luminal-like carcinoma cells in CMGCs, which may suppresses the development of malignant phenotypes in CMGCs.

Expression of receptor-type tumour endothelial marker 8 in carcinoma cells showing luminal progenitor-like phenotypes in canine mammary gland carcinomas.

This study aimed to investigate the expression of receptor-type tumour endothelial marker 8 (TEM8RT) in canine mammary gland carcinomas (CMGCs) using immunohistochemistry and to evaluate the association between carcinoma cell TEM8RT expression and tumour histological features, histological grades and the differentiation status of neoplastic epithelial cells. TEM8RT expression was more frequently detected in simple carcinomas (tubular and tubulopapillary) than in solid carcinomas, and it was significantly correlated with histological grade Ⅰ tumours and a low mitotic index. Additionally, TEM8RT+ carcinoma cells were more frequently found in CMGCs showing luminal progenitor-like phenotypes, such as Notch1+, CK19+/CK5+/CD49f+ and CK19+/CK5-/CD49f+. Double-labelling immunofluorescence detection techniques confirmed that most TEM8RT+ carcinoma cells expressed CD49f, Notch1 and CK19. However, TEM8RT immunoreactivity was not found in carcinoma cells expressing GATA3, which upregulates mature luminal cell differentiation. Furthermore, TEM8RT+ carcinoma cells were detected in a few CMGCs showing basal/stem cell-like phenotypes such as CK19-/CK5+/CD49f+ and CK19-/CK5+/CD49f-. These findings indicate that TEM8RT is expressed in luminal progenitor-like carcinoma cells in CMGCs. Since TEM8 enhances self-renewal in human mammary stem/progenitor cells, it also may be involved in maintenance of luminal progenitor-like carcinoma cells, resulting in prevention of their transition to basal/stem cell-like carcinoma cells and development of less malignant CMGCs. Therefore, TEM8RT may be useful for indicating prognostic outcomes and identifying the possible ontogeny of carcinoma cells in mammary gland tumours.

Histidine decarboxylase deficiency inhibits NBP-induced extramedullary hematopoiesis by modifying bone marrow and spleen microenvironments.

Histidine decarboxylase (HDC), a histamine synthase, is expressed in various hematopoietic cells and is induced by hematopoietic cytokines such as granulocyte colony-stimulating factor (G-CSF). We previously showed that nitrogen-containing bisphosphonate (NBP)-treatment induces extramedullary hematopoiesis via G-CSF stimulation. However, the function of HDC in NBP-induced medullary and extramedullary hematopoiesis remains unclear. Here, we investigated changes in hematopoiesis in wild-type and HDC-deficient (HDC-KO) mice. NBP treatment did not induce anemia in wild-type or HDC-KO mice, but did produce a gradual increase in serum G-CSF levels in wild-type mice. NBP treatment also enhanced Hdc mRNA expression and erythropoiesis in the spleen and reduced erythropoiesis in bone marrow and the number of vascular adhesion molecule 1 (VCAM-1)-positive macrophages in wild-type mice, as well as increased the levels of hematopoietic progenitor cells and proliferating cells in the spleen and enhanced expression of bone morphogenetic protein 4 (Bmp4), CXC chemokine ligand 12 (Cxcl12), and hypoxia inducible factor 1 (Hif1) in the spleen. However, such changes were not observed in HDC-KO mice. These results suggest that histamine may affect hematopoietic microenvironments of the bone marrow and spleen by changing hematopoiesis-related factors in NBP-induced extramedullary hematopoiesis.

Changes in histidine decarboxylase expression influence extramedullary hematopoiesis in postnatal mice.

Histidine decarboxylase (HDC), histamine synthase, is expressed in hematopoietic stem cells and in lineage-committed progenitors in the bone marrow (BM). However, the role of histamine in hematopoiesis is not well described. To evaluate the role of histamine in hematopoiesis, we analyzed the changes in HDC expression at hematopoietic sites, the BM, spleen, and liver of 2-, 3-, and 6-week-old wild-type mice. We also performed morphological analyses of the hematopoietic sites using HDC-deficient (HDC-KO) mice. In wild-type adults, HDC expression in the BM was higher than that in the spleen and liver and showed an age-dependent increase. Histological analysis showed no significant change in the adult BM and spleen of HDC-KO mice compared to wild-type mice. In the liver, HDC expression was temporarily increased at 3 weeks and decreased at 6 weeks of age. Morphological analysis of the liver revealed more numerous hematopoietic colonies and megakaryocytes in HDC-KO mice compared to wild-type mice at 2 and 3 weeks of age, whereas no changes were observed in adults. Most of these hematopoietic colonies consisted of B220-positive B-lymphocytes and TER119-positive erythroblasts and were positive for the cell proliferation marker PCNA. Notably, these hematopoietic colonies declined in HDC-KO mice upon N-acetyl histamine treatment. A significant increase in the expression of hematopoiesis-related cytokines, Il3, Il7, Epo, Gcsf, and Cxcl12 mRNA was observed in the liver of 3-week-old HDC-KO mice compared to wild-type mice. These results suggest that histamine-deficiency may maintain an microenvironment suitable for hematopoiesis by regulating hematopoiesis-related cytokine expression in the liver of postnatal mice.

Expressions of vascular endothelial growth factor receptors, Flk1 and Flt1, in rat skin mast cells during development.

Vascular endothelial growth factor-A (VEGF-A) is a principal regulator of hematopoiesis as well as angiogenesis. However, the functions of VEGF-A and its receptors (VEGFRs) in the differentiation of mast cells (MCs) in the skin remain unclear. The aim of this study was to determine the expression patterns of two VEGFRs (Flk1 and Flt1) in the skin MCs during development and maturation in rats. From the 17th days of embryonic development (E17) to 1 day after birth (Day 1), most of skin MCs were immature cells containing predominant alcian blue (AB)+ rather than safranin O (SO)+ granules (AB>SO MCs). AB>SO MC proportions gradually decreased, while mature ABSO MCs had significantly decreased, and AB

Big Insulin-like Growth Factor 2-Producing Tumor in a Hypoglycemic Dog.

A 10-year-old female Papillon dog that had previously developed a mammary tumor was admitted for treatment of a hypoglycemic attack. Blood examination showed severe hypoglycemia and decreased blood insulin concentration. Computed tomography indicated multiple tumors in the cranial and caudal lobes of the right lung. These tumors were resected surgically and diagnosed as pulmonary adenocarcinomas by histopathologic examination. Hypoglycemia was temporarily improved after the resection, but a hypoglycemic event occurred 2 months after the surgery. Immunohistochemistry of the tumor demonstrated the expression of insulin-like growth factor 2 in tumor cells. Western blot analysis revealed the expression of high-molecular-weight (big)-insulin-like growth factor 2 in the tumor region. Insulin-like growth factor 2 mRNA expression was also confirmed in the tumor using reverse transcription-polymerase chain reaction. These findings indicate the diagnosis of non-islet cell tumor-induced hypoglycemia caused by big-insulin-like growth factor 2 produced by the tumor in the dog. This report provides information on differentiating tumors that cause paraneoplastic hypoglycemia.

Dynamics of Platelet Behaviors as Defenders and Guardians: Accumulations in Liver, Lung, and Spleen in Mice.

Systemic platelet behaviors in experimental animals are often assessed by infusion of isotope-labeled platelets and measuring them under anesthesia. However, such procedures alter, therefore may not reveal, real-life platelet behaviors. 5-Hydroxytryptamine (5HT or serotonin) is present within limited cell-types, including platelets. In our studies, by measuring 5HT as a platelet-marker in non-anesthetized mice, we identified stimulation- and time-dependent accumulations in liver, lung, and/or spleen as important systemic platelet behaviors. For example, intravenous, intraperitoneal, or intragingival injection of lipopolysaccharide (LPS, a cell-wall component of Gram-negative bacteria), interleukin (IL)-1, or tumor necrosis factor (TNF)-α induced hepatic platelet accumulation (HPA) and platelet translocation into the sinusoidal and perisinusoidal spaces or hepatocytes themselves. These events occurred "within a few hours" of the injection, caused hypoglycemia, and exhibited protective or causal effects on hepatitis. Intravenous injection of larger doses of LPS into normal mice, or intravenous antigen-challenge to sensitized mice, induced pulmonary platelet accumulation (PPA), as well as HPA. These reactions occurred "within a few min" of the LPS injection or antigen challenge and resulted in shock. Intravenous injection of 5HT or a catecholamine induced a rapid PPA "within 6 s." Intravenous LPS injection, within a minute, increased the pulmonary catecholamines that mediate the LPS-induced PPA. Macrophage-depletion from liver and spleen induced "day-scale" splenic platelet accumulation, suggesting the spleen is involved in clearing senescent platelets. These findings indicate the usefulness of 5HT as a marker of platelet behaviors, and provide a basis for a discussion of the roles of platelets as both "defenders" and "guardians."

Decisive differences in the bone repair processes of the metaphysis and diaphysis in young mice.

Fractures are common traumatic injuries that mainly occur in the metaphyses of long bones such as the proximal humerus, distal radius, and proximal femur. However, most studies of fracture repair processes have focused on the diaphyseal region. In this study, we compared the bone repair processes of the metaphysis and the diaphysis of the mouse tibia. Bone apertures were formed in the tibial metaphysis and diaphysis. At indicated times after surgery, samples were collected, and the healing process was investigated using micro-computed tomography, as well as histological, immunohistochemical, and mRNA expression analyses. In the metaphysis, cartilage formation was not detected on the periosteal side. The bone aperture was filled with newly formed bone produced from bone marrow at day 7. In the case of the diaphysis, cartilage was formed around the aperture at day 4 and sequentially replaced by bone on the periosteal side. The bone aperture was filled with newly formed bone at day 14. In the bone marrow, expression of the osteogenic markers such as alkaline phosphatase, osteocalcin, and type I collagen, appeared earlier with metaphyseal injury than with diaphyseal injury. The mRNA expression of chondrogenesis markers was markedly upregulated in the diaphysis compared with that in the metaphysis on the periosteal side. These results indicate differences in the bone repair processes of the two regions, suggesting functional heterogeneity of the periosteum and bone marrow mesenchymal cells in response to bone fractures.

Symmetrical retrograde actin flow in the actin fusion structure is involved in osteoclast fusion.

The aim of this study was to elucidate the role of the zipper-like structure (ZLS), a podosome-related structure that transiently appears at the cell contact zone, in osteoclast fusion. Live-cell imaging of osteoclasts derived from RAW264.7 cells transfected with EGFP-actin revealed consistent symmetrical retrograde actin flow in the ZLS, but not in the podosome cluster, the podosome ring or the podosome belt. Confocal imaging showed that the distributions of F-actin, vinculin, paxillin and zyxin in the ZLS were different from those in the podosome belt. Thick actin filament bundles running outside the ZLS appeared to recruit non-muscle myosin IIA. The F-actin-rich domain of the ZLS contained actin-related protein 2/3 complex (Arp2/3). Inhibition of Arp2/3 activity disorganized the ZLS, disrupted actin flow, deteriorated cell-cell adhesion and inhibited osteoclast hypermultinucleation. In contrast, ML-7, an inhibitor of myosin light chain kinase, had little effect on the structure of ZLS and promoted osteoclast hypermultinucleation. These results reveal a link between actin flow in the ZLS and osteoclast fusion. Osteoclast fusion was promoted by branched actin elongation and negatively regulated by actomyosin contraction.

Comprehensive genetic exploration of selective tooth agenesis of mandibular incisors by exome sequencing.

Tooth agenesis is described as the absence of one or more teeth. It is caused by a failure in tooth development and is one of the most common human developmental anomalies. We herein report genomic analyses of selective mandibular incisor agenesis (SMIA) using exome sequencing. Two Japanese families with SMIA were subjected to exome sequencing, and family with sequence similarity 65 member A (FAM65), nuclear factor of activated T-cells 3 (NFATC3) and cadherin-related 23 gene (CDH23) were detected. In the follow-up study, 51 Japanese and 32 Korean sporadic patients with SMIA were subjected to exome analyses, and 18 reported variants in PAX9, AXIN2, EDA, EDAR, WNT10A, BMP2 and GREM2 and 27 variants of FAM65, NFATC3 and CDH23 were found in 38 patients. Our comprehensive genetic study of SMIA will pave the way for a full understanding of the genetic etiology of SMIA and provide targets for treatment.

Pulmonary platelet accumulation induced by catecholamines: Its involvement in lipopolysaccharide-induced anaphylaxis-like shock.

Intravenously injected lipopolysaccharides (LPS) rapidly induce pulmonary platelet accumulation (PPA) and anaphylaxis-like shock (ALS) in mice. Macrophages reportedly release catecholamines rapidly upon stimulation with LPS. Here, we examined the involvement of macrophage-derived catecholamines in LPS-induced PPA and ALS. A catecholamine or Klebsiella O3 (KO3) LPS was intravenously injected into mice, with 5-hydroxytryptamine in the lung being measured as a platelet marker. The tested catecholamines induced PPA, leading to shock. Their minimum shock-inducing doses were at the nmol/kg level. The effects of epinephrine and norepinephrine were inhibited by prazosin (α1 antagonist) and by yohimbine (α2 antagonist), while dopamine's were inhibited only by prazosin. Use of synthetic adrenergic α1- and/or α2-agonists, platelet- or macrophage-depleted mice, a complement C5 inhibitor and C5-deficient mice revealed that (a) α2-receptor-mediated PPA and shock depend on both macrophages and complements, while α1-receptor-mediated PPA and shock depend on neither macrophages nor complements, (b) the PPA and ALS induced by KO3-LPS depend on α1- and α2-receptors, macrophages, and complements, and (c) KO3-LPS-induced PPA is preceded by catecholamines decreasing in serum. Together, these results suggest the following. (i) Catecholamines may stimulate macrophages and release complement C5 via α2-receptors. (ii) Macrophage-derived catecholamines may mediate LPS-induced PPA and ALS. (iii) Moderate PPA may serve as a defense mechanism to remove excess catecholamines from the circulation by promoting their rapid uptake, thus preventing excessive systemic effects. (iv) The present findings might provide an insight into possible future pharmacological strategies against such diseases as shock and acute respiratory distress syndrome.

Nitrogen-containing bisphosphonate induces a newly discovered hematopoietic structure in the omentum of an anemic mouse model by stimulating G-CSF production.

We previously reported that the injection of nitrogen-containing bisphosphonate (NBP) induced the site of erythropoiesis to shift from the bone marrow (BM) to the spleen. Our previous study established a severely anemic mouse model that was treated with a combination of NBP with phenylhydrazine (PHZ), which induced newly discovered hematopoietic organs in the omentum. No reports have shown that new hematopoietic organs form under any condition. We characterized the structures and factors related to the formation of these new organs. Splenectomized mice were treated with NBP to inhibit erythropoiesis in the BM and then injected with PHZ to induce hemolytic anemia. The mice showed severe anemia and wine-colored structures appeared in the omentum. Some hematopoietic cells, including megakaryocytes, and well-developed sinuses were observed in these structures. Numerous TER119-positive erythroblasts were located with cells positive for PCNA, a cell proliferation marker. C-kit-positive cells were detected and mRNAs related to hematopoiesis were expressed in these structures. Moreover, TER119-positive erythroblasts emerged and formed clusters and hematopoiesis-related factors were detected in the omentum of mice treated with NBP and PHZ. The levels of G-CSF in the serum and hematopoietic progenitor cells (HPCs) in the peripheral blood were increased upon treatment with both NBP and PHZ. These results suggest that the induced hematopoietic structures act as the sites of erythropoiesis and that NBP-induced G-CSF production causes HPC mobilization, homing and colonization in the omentum because they constitutively express some factors, including SDF-1; thus, the newly discovered hematopoietic structure in this study might be formed.

The expression of embryonic globin mRNA in a severely anemic mouse model induced by treatment with nitrogen-containing bisphosphonate.

BACKGROUND: Mammalian erythropoiesis can be divided into two distinct types, primitive and definitive, in which new cells are derived from the yolk sac and hematopoietic stem cells, respectively. Primitive erythropoiesis occurs within a restricted period during embryogenesis. Primitive erythrocytes remain nucleated, and their hemoglobins are different from those in definitive erythrocytes. Embryonic type hemoglobin is expressed in adult animals under genetically abnormal condition, but its later expression has not been reported in genetically normal adult animals, even under anemic conditions. We previously reported that injecting animals with nitrogen-containing bisphosphonate (NBP) decreased erythropoiesis in bone marrow (BM). Here, we induced severe anemia in a mouse model by injecting NBP injection in combination with phenylhydrazine (PHZ), and then we analyzed erythropoiesis and the levels of different types of hemoglobin. METHODS: Splenectomized mice were treated with NBP to inhibit erythropoiesis in BM, and with PHZ to induce hemolytic anemia. We analyzed hematopoietic sites and peripheral blood using morphological and molecular biological methods. RESULTS: Combined treatment of splenectomized mice with NBP and PHZ induced critical anemia compared to treatment with PHZ alone, and numerous nucleated erythrocytes appeared in the peripheral blood. In the BM, immature CD71-positive erythroblasts were increased, and extramedullary erythropoiesis occurred in the liver. Furthermore, embryonic type globin mRNA was detected in both the BM and the liver. In peripheral blood, spots that did not correspond to control hemoglobin were observed in 2D electrophoresis. ChIP analyses showed that KLF1 and KLF2 bind to the promoter regions of ß-like globin. Wine-colored capsuled structures were unexpectedly observed in the abdominal cavity, and active erythropoiesis was also observed in these structures. CONCLUSION: These results indicate that primitive erythropoiesis occurs in adult mice to rescue critical anemia because primitive erythropoiesis does not require macrophages as stroma whereas macrophages play a pivotal role in definitive erythropoiesis even outside the medulla. The cells expressing embryonic hemoglobin in this study were similar to primitive erythrocytes, indicating the possibility that yolk sac-derived primitive erythroid cells may persist into adulthood in mice.

Regulation of Osteoclast Multinucleation by the Actin Cytoskeleton Signaling Network.

Although it is known that osteoclasts are multinucleated cells that are responsible for bone resorption, the mechanism by which their size is regulated is unclear. We previously reported that an actin-rich superstructure, termed the zipper-like structure, specifically appears during the fusion of large osteoclast-like cells (OCLs). Actin cytoskeleton reorganization in osteoclasts is regulated by a signaling network that includes the macrophage colony-stimulating factor (M-CSF) receptor, a proto-oncogene, Src, and small GTPases. Here, we examined the role of actin reorganization in the multinucleation of OCLs differentiated from RAW 264.7 cells using various pharmacological agents. Jasplakinolide, which stabilizes actin stress fibers, induced the development of small OCLs, and the Src inhibitor SU6656 and the dynamin inhibitor dynasore impaired the maintenance of the podosome belt and the zipper-like structure. These inhibitors decreased the formation of large OCLs but increased the number of small OCLs. M-CSF is known to stimulate osteoclast fusion. M-CSF signaling via Src up-regulated Rac1 activity but down-regulated Rho activity. Rac1 and Rho localized to the center of the zipper-like structure. Rho activator II promoted the formation of small OCLs, whereas the Rho inhibitor Y27632 promoted the generation of large OCLs. These results suggest that the status of the actin cytoskeleton signaling network determines the size of OCLs during cell fusion.

In situ proliferation and differentiation of macrophages in dental pulp.

The presence of macrophages in dental pulp is well known. However, whether these macrophages proliferate and differentiate in the dental pulp in situ, or whether they constantly migrate from the blood stream into the dental pulp remains unknown. We have examined and compared the development of dental pulp macrophages in an organ culture system with in vivo tooth organs to clarify the developmental mechanism of these macrophages. The first mandibular molar tooth organs from ICR mice aged between 16 days of gestation (E16) to 5 days postnatally were used for in vivo experiments. Those from E16 were cultured for up to 14 days with or without 10% fetal bovine serum. Dental pulp tissues were analyzed with immunohistochemistry to detect the macrophages and with reverse transcription and the polymerase chain reaction (RT-PCR) for the detection of factors related to macrophage development. The growth curves for the in vivo and in vitro cultured cells revealed similar numbers of F4/80-positive macrophages in the dental pulp. RT-PCR analysis indicated the constant expression of myeloid colony-stimulating factor (M-CSF) in both in-vivo- and in-vitro-cultured dental pulp tissues. Anti-M-CSF antibodies significantly inhibited the increase in the number of macrophages in the dental pulp. These results suggest that (1) most of the dental pulp macrophages proliferate and differentiate in the dental pulp without a supply of precursor cells from the blood stream, (2) M-CSF might be a candidate molecule for dental pulp macrophage development, and (3) serum factors might not directly affect the development of macrophages.

Kupffer cells support extramedullary erythropoiesis induced by nitrogen-containing bisphosphonate in splenectomized mice.

Our previous study indicated that injecting nitrogen-containing bisphosphonate (NBP) induced the site of erythropoiesis to shift from the bone marrow (BM) to the spleen. This was due to the depletion of BM-resident macrophages, which support erythropoiesis. In this study, we examined NBP treatment-induced extramedullary hematopoiesis in splenectomized mice, focusing on hepatic hematopoiesis. NBP-treated mice did not display anemia or significant change in erythropoietin production, while megakaryopoiesis and erythropoiesis were constantly observed in the liver. Erythroblastic islands were detected in the sinusoidal lumen. Kupffer cells expressed VCAM-1 following NBP treatment, which is an important factor for erythroblast differentiation. Cl(2)MBP-liposome treatment depleted the erythroblastic islands, and decreased the number of hematopoietic cells in the liver, as determined by colony forming assays. Together, these results indicate that Kupffer cells support erythropoiesis, acting as stromal cells in the liver, and that they might act as a niche for hematopoietic precursor cells in an emergency.

Roles of platelets and macrophages in the protective effects of lipopolysaccharide against concanavalin A-induced murine hepatitis.

Platelets are reportedly causal in hepatitis. We previously showed that in mice, lipopolysaccharide (LPS) induces a reversible and macrophage-dependent hepatic platelet accumulation (HPA), including translocation of platelets into Disse spaces and their entry into hepatocytes. Concanavalin A (ConA), which induces hepatitis in mice via both T cells and macrophages, also induces HPA. Here, we examined the relationship between HPA and ConA-hepatitis. ConA-hepatitis and HPA were evaluated by serum transaminases, hepatic 5-hydroxytryptamine, and/or electron microscopy. Unlike LPS-induced HPA, ConA-induced HPA was only moderately dependent on phagocytic macrophages. Against expectations, platelet-depletion significantly exacerbated ConA-hepatitis, and anti-P-selectin antibody and P-selectin receptor blockade reduced both ConA-induced HPA and hepatitis. Prior induction of HPA by pretreatment with low-dose LPS powerfully reduced ConA-hepatitis. Such protection by LPS-pretreatment was not effective in mice depleted of phagocytic macrophages. In platelet-depleted mice, LPS-pretreatment severely exacerbated ConA-hepatitis. In mice depleted of both macrophages and platelets, neither ConA nor LPS-pretreatment+ConA induced hepatitis. In mice deficient in IL-1α and IL-1ß (but not in TNFα), ConA-induced hepatitis was mild, and a protective effect of LPS was not detected. These results suggest that (i) there are causal and protective types of HPA, (ii) the causal type involves hepatic aggregation of platelets, which may be induced by platelet stimulants leaked from injured hepatocytes, (iii) the protective type is inducible by administration of prior low-dose LPS in a manner dependent on phagocytic (or F4/80-positive) macrophages, and (iv) IL-1 is involved in both the causal and protective types.