Myeloid Precursor Cells Research Articles

Hepatic Stellate Cells Regulate Immune Response by Way of Induction of Myeloid Suppressor Cells in Mice Δσ

Although organ transplants have been applied for decades, outcomes of somatic cell transplants remain disappointing, presumably due to lack of appropriate supporting stromal cells. Thus, cotransplantation with liver stromal cells, hepatic stellate cells (HSC), achieves long-term survival of islet allografts in mice by way of induction of effector T cell apoptosis and generation of regulatory T (Treg) cells. In this study we provide evidence both in vitro and in vivo that HSC can promote generation of myeloid-derived suppressor cells (MDSC). HSC-induced MDSC demonstrate potent immune inhibitory activity. Induction of MDSC is dependent on an intact interferon gamma signaling pathway in HSC and is mediated by soluble factors, suggesting that the specific tissue stromal cells, such as HSC, play a crucial role in regulating immune response by way of inflammation-induced generation of MDSC. Large amounts of MDSC can be propagated in vitro from bone marrow-derived myeloid precursor cells under the influence of HSC. Cotransplantation with in vitro generated MDSC can effectively protect islet allografts from host immune attack. Local delivery of potent immune suppressor cells for cell transplants holds great clinical application potential.

Pediatric Myelodysplastic Syndrome With Cytoplasmic Vacuolation in Myeloid Precursors

A 6-year-old boy presented with pancytopenia. Bone marrow morphology showed dyspoiesis and cytoplasmic vacuolation in myeloid precursor cells. Cytoplasmic vacuoles are described in erythroid cells in myelodysplastic syndrome (MDS) but are extremely rare in myeloid precursor cells. We ruled out viral and autoimmune etiology, hypocupremia, Pearson syndrome, and chromosomal abnormalities. Finally, a diagnosis of MDS of refractory cytopenia of childhood subtype was made. The patient then underwent an allogenic stem cell transplant that resulted in normalization of the complete blood counts and bone marrow morphology. However, he later developed late graft failure; this was followed by a second transplant after which he died of sepsis and multiorgan failure. The case is presented here for the rare morphologic features, hitherto not earlier described in pediatric MDS.

Microscope-based label-free microfluidic cytometry

A microscope-based label-free microfluidic cytometer capable of acquiring two dimensional light scatter patterns from single cells, pattern analysis of which determines cellular information such as cell size, orientation and inner nanostructure, was developed. Finite-difference time-domain numerical simulations compared favorably with experimental scatter patterns from micrometer-sized beads and cells. The device was capable of obtaining light scattering patterns from the smallest mature blood cells (platelets) and cord blood hematopoietic stem/progenitor cells (CD34 + cells) and myeloid precursor cells. The potential for evaluation of cells using this label-free microfluidic cytometric technique was discussed.

Chronic Myeloid Leukemia Presenting with Visual and Auditory Impairment in an Adolescent: An Insight to Management Strategies

A 15-year-old girl presented with progressive deterioration in vision and hearing over 1 week. A huge spleen was palpated below the left costal margin laying down to inguinal region. Blood count showed hyperleukocytosis with a white blood cell count of 455 × 10(9)/l. Peripheral smear yielded myeloid precursor cells with basophilia. Bone marrow aspiration revealed a blast count of 5% morphologically and 4% by flow cytometry. Fundoscopic examination revealed bilateral retinal exudates, edema and hemorhages. Partial sensorioneural hearing loss was also detected on the right ear. The diagnosis of chronic myeloid leukemia was confirmed by positive t(9;22) by RT-PCR. After commencing on hydroxyurea and intrathecal methotrexate-prednisolone, progressive improvement in hearing and vision was obtained. In our brief report, we aimed to emphasize rare presentation with visual and hearing impairment of chronic myeloid leukemia during childhood, especially in "chronic phase".

Generation of microglial cells from mouse embryonic stem cells

Microglia, the resident immune cells of the brain, are difficult to obtain in high numbers and purity using currently available methods; to date, microglia for experimental research are mainly isolated from the brain or from mixed glial cultures. In this paper, we describe a basic protocol for the in vitro differentiation of mouse embryonic stem (ES) cells into microglial precursor cells. Microglia are obtained by a protocol consisting of five stages: (i) cultivation of ES cells, (ii) formation and differentiation of embryoid bodies, (iii) differentiation into neuroectodermal lineage and isolation of myeloid precursor cells, (iv) differentiation into microglial precursor cells and (v) cultivation of ES cell-derived microglial precursors (ESdMs). The protocol can be completed in 60 d and results in stably proliferating ESdM lines, which show inducible transcription of inflammatory genes and cell marker expression comparable with primary microglia. Furthermore, ESdMs are capable of chemokine-directed migration and phagocytosis, which are major functional features of microglia.

PTPIP51—a myeloid lineage specific protein interacts with PTP1B in neutrophil granulocytes

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) was identified as an in vitro interacting partner of protein tyrosine phosphatase 1B (PTP1B) and T-cell protein tyrosine phosphatase (TCPTP). The full-length form of PTPIP51 encompasses 470aas and has a molecular weight of 52 kDa. The physiological function is poorly understood but an involvement in differentiation processes and apoptosis has been suggested. Preliminary observations suggested differences in PTPIP51 expression in blood cells. To analyze a possible involvement of PTPIP51 in hematopoietic processes, we studied its expression in samples of peripheral venous blood (PVB), umbilical cord blood (UCB) and human bone marrow (HBM). In both, PVB and UCB PTPIP51 expression was restricted to neutrophil granulocytes. In HBM samples, besides in mature neutrophil ganulocytes PTPIP51 protein and mRNA was present in myeloid precursor cells of neutrophils. The expression of PTPIP51 in neutrophil granulocytes was corroborated by immunoblot analysis exhibiting different molecular weight forms of PTPIP51 protein. Anti-peptide antibodies, identifying specific regions of the PTPIP51 protein (C-terminus, N-terminus and aas114–129) revealed a distinct isoform expression pattern in neutrophil granulocytes of different sources. In PVB and UCB neutrophil granulocytes reacted positive for all three peptide antibodies. In contrast, neutrophils of HBM express solely an N-terminal variant of PTPIP51 protein, lacking the C-terminal and aas114–129 sequence. Immunocytochemical results displayed a strict co-localization of PTPIP51 and PTP1B in PVB and UCB. The interaction of both proteins was verified by a proximity ligation assay. Neither proliferating cells, as identified by PCNA immunostaining, nor apoptotic cells, labeled by TUNEL assay, displayed an immunoreactivity for PTPIP51 in HBM. In fact, PTPIP51 expression was restricted to myeloid precursor cells undergoing differentiation. In blood cells therefore, PTPIP51 expression is restricted to differentiating and mature neutrophil granulocytes.

The roles of bioactive sphingolipids in resveratrol-induced apoptosis in HL60 acute myeloid leukemia cells

Acute promyelocytic leukemia results from a translocation between 15 and 17 chromosomes that produce PML/RARα fusion protein. PML/RARα inhibits differentiation of myeloid precursor cells at stem cell level. Resveratrol is a phytoalexin that exerts cytotoxic effects on cancer cells. Ceramides have crucial roles in cell growth, proliferation, differentiation, drug resistance, and apoptosis. In this study, we examined the possible cytotoxic effects of resveratrol on acute myeloid leukemia cells and determined the roles of ceramide-metabolizing genes in resveratrol-induced apoptosis, in addition to investigating the possibility of increasing the sensitivity of HL60 cells to resveratrol by manipulating sphingolipids. Cytotoxic effects of resveratrol, C8:ceramide, PDMP, and SK-1 inhibitor were determined by XTT cell proliferation assay. Changes in caspase-3 enzyme activity and mitochondrial membrane potential (MMP) were measured using caspase-3 colorimetric assay and JC-1 MMP detection kit. Expression levels of ceramide-metabolizing genes were examined by RT-PCR. The results revealed that manipulations of ceramide metabolism toward generation or accumulation of apoptotic ceramides increased apoptotic effects of resveratrol in HL60 cells, synergistically. More importantly, gene expression analyses revealed that resveratrol-induced apoptosis via increasing expression levels of ceramide-generating genes and decreasing expression levels of antiapoptotic sphingosine kinase-1 and glucosylceramide synthase genes. These results showed for the first time that increasing intracellular levels of ceramides by biochemical approaches has also increased sensitivity of HL60 cells to resveratrol. We also showed that resveratrol induces apoptosis through manipulating ceramide-metabolizing genes that resulted in the accumulation of ceramides in HL60 cells.

Subsets, expansion and activation of myeloid-derived suppressor cells

Tumor cells and microorganisms manipulate the immune system to minimize any counter response in order to survive. Myeloid-derived suppressor cells (MDSC) in the mouse represent activated Gr-1(+) CD11b(+) myeloid precursor cells. Activation may occur through endogenous or exogenous factors leading to the suppression of immune responses. Under steady state conditions the same precursors differentiate into dendritic cells, macrophages and neutrophils. Their linkage to tumor progression and several suppression mechanisms employing the arginine metabolism are well documented, but knowledge of their role in chronic infections, autoimmune diseases and graft-versus-host reactions is just emerging. Several factors have been described to promote MDSC expansion and activation in bone marrow, spleen and tumor sites. New evidence suggests that the Gr-1 antibody itself may differentially trigger myelopoiesis under steady state conditions or induce apoptosis in inflammatory situations after binding to a common epitope expressed on Ly-6C and Ly-6G molecules, respectively. Moreover, two subsets of neutrophil- and monocyte-related MDSC have been described in tumor-bearing and healthy mice. In the present review, we summarize some early work leading to recent findings on these two MDSC subsets, the factors supporting MDSC expansion and activation, as well as novel insights on Gr-1 antibody functions.

Detection of isocitrate dehydrogenase 1 mutation R132H in myelodysplastic syndrome by mutation-specific antibody and direct sequencing

Sequencing of the acute myeloid leukemia genome revealed somatic mutations in isocitrate dehydrogenase-1. Acute myeloid leukemia frequently develops from myelodysplastic syndrome. In order to test whether myelodysplastic syndrome also carries isocitrate dehydrogenase-1 mutations, we stained a series of bone marrow samples from patients with myelodysplastic syndrome using an antibody specific for the R132H mutation. Three out of 71 patients exhibited antibody binding to myeloid precursor cells. The presence of the R132H mutation was confirmed by DNA sequencing. We demonstrated that isocitrate dehydrogenase-1 mutations occur in myelodysplasia preceding acute myeloid leukemia and that the R132H alteration can be detected by immunohistochemistry.

Heterogeneity in a mouse model of histiocytosis: transformation of Langerin+ dendritic cells, macrophages, and precursors

Neoplastic diseases of macrophages (M phi) and dendritic cells (DC), collectively called histiocytoses, are relatively rare. The etiology of most forms of histiocytosis is poorly understood, and the development of animal models is crucial for further research in this field. Previously, an animal model for malignant histiocytosis (MH), involving transformed histiocytic cells, has been generated by infecting mice with malignant histiocytosis sarcoma virus (MHSV). However, increased insight into the heterogeneity of M phi and DC, and the associated reappraisal of human proliferative diseases involving these cells inspired us to re-evaluate the mouse model. We analyzed spleen, bone marrow, and lymph nodes of susceptible mice at various time points after infection. From day 11 onwards, a heterogeneous population of cells, consisting of CD8 alpha(+) Langerin(+) DC, ER-MP58(+) CD11b(+) myeloid precursor cells, CD169(+) metallophilic M phi, and CD71(hi) erythroblasts, was affected by viral transformation. In different mice, these subsets expanded at different rates in different organs, causing a variable disease profile in terminal stages. Cell lines, which were generated from MHSV-transformed tumors, showed a DC-like morphology and phenotype, and appeared to be arrested in different stages of maturation. Upon injection into healthy mice, different preferential homing patterns were observed for the various cell lines, and the cells acquired distinct phenotypes depending on the organ of homing. This indicates that these transformed cells adapt to their microenvironment by switching between precursor, DC/Langerhans cell, and M phi phenotypes. Our results demonstrate that the MHSV model represents a heterogeneous neoplastic disease with characteristics of M phi/DC sarcomas.

Primary granulocytic sarcoma of ovary: A rare case report

Granulocytic sarcomas are extra medullary tumors of malignant myeloid precursor cells.1 It usually involves skin, lymph node, bone, spine and rarely ovary. Granulocytic sarcomas of ovary can occur with known acute non‐lymphatic leukemia and chronic myeloproliferative disorders but primary ovarian involvement of granulocytic sarcomas in patient with no other hematologic disease is extremely rare.3 So it is very difficult to have accurate diagnosis because primary granulocytic sarcomas may be unsuspected at the time of diagnosis.

Invasive Aspergillosis in Solid Organ Transplant Recipients

This chapter discusses the current status and evolving trends in the epidemiology, risk factors, diagnostic laboratory assays, and the approach to antifungal prophylaxis and treatment of invasive aspergillosis in Solid Organ Transplant (SOT) recipients. Most invasive fungal infections in these high-risk patients occur within the first month posttransplant; the median time to onset of invasive aspergillosis after renal replacement therapy and retransplantation was 13 and 28 days, respectively, in one study. Other factors associated with invasive aspergillosis in liver transplant recipients include transplantation for fulminate hepatic failure, cytomegalovirus (CMV) infection, and prolonged intensive care unit stay. A retrospective survey documented invasive pulmonary aspergillosis in 7.5% (19/251) of lung transplant recipients, of whom 47% (9/19) had disseminated aspergillosis. In a survey of antifungal prophylactic strategies in lung transplant units in the United States, aerosolized amphotericin B was the most frequently employed antifungal prophylactic agent. In order of preference, the prophylactic agents used in lung transplant centers in this study were inhaled amphotericin B (61%), itraconazole (46%), parenteral amphotericin formulations (25%), and fluconazole (21%); many centers used more than one agent. Preemptive therapy, where antifungal prophylaxis is directed towards lung transplant recipients colonized with Aspergillus spp. immediately before or within 6 to 9 months after transplantation, is another approach to the prevention of invasive aspergillosis in lung transplant recipients.

Mechanism of Myeloid-Derived Suppressor Cell Differentiation in Cancer.

Abstract SCI-31Myeloid-derived suppressor cells (MDSC) represent an intrinsic part of myeloid cell lineage and comprised of myeloid progenitors and precursors of myeloid cells. In healthy host upon generation in bone marrow immature myeloid cells (IMC) quickly differentiate into mature granulocytes, macrophages, or dendritic cells. In a number of pathological conditions (cancer, various infections diseases, sepsis, trauma, bone marrow transplantation, autoimmune abnormalities) increased production of IMC is associated with partial block of their differentiation and most importantly pathological activation of these cells manifests in up-regulation of arginase, inducible nitric oxide synthase (iNOS) and NO production, increased level of reactive oxygen species (ROS). This results in expansion of IMC with immune suppressive activity. Accumulation of MDSC was detected in practically all mouse tumor models and in patients with different types of cancer. In mice, MDSCs are characterized by the co-expression of myeloid lineage differentiation antigen Gr1 and CD11b. In humans, MDSC are currently defined as CD14-CD11b+ cells or more narrowly as cells that express the common myeloid marker CD33 but lack the expression of markers of mature myeloid and lymphoid cells and the MHC class II molecule HLA-DR. Recently, the morphological heterogeneity of these cells in mice was defined more precisely based on the expression of cell-surface markers Ly6G and Ly6C. Granulocytic MDSCs have a CD11b+Ly6G+Ly6Clow phenotype, whereas MDSCs with monocytic morphology are CD11b+Ly6G-Ly6Chigh. These two subpopulations may have different functions. Accumulation of MDSC is caused by different soluble factors. Recent studies have demonstrated that factors implicated in regulating the expansion of MDSCs can be provisionally split into two main groups with partially overlapping activity. The first group includes factors that are produced primarily by tumor cells and promote the expansion of MDSC through myelopoiesis stimulation, which is associated with inhibition of myeloid-cell differentiation. These factors include stem-cell factor (SCF), macrophage colony-stimulating factor (M-CSF), IL-6, granulocyte/macrophage colony-stimulating factor (GM-CSF) and vascular endothelial growth factor (VEGF) and others. Signalling pathways triggered by most of these factors in MDSCs converge on signal transducer and activator of transcription 3 (STAT3). One of the potential targets for STAT3 was recently identified as S100A8/A9 proteins. Accumulation of these proteins in myeloid progenitors prevents their differentiation and results in expansion of MDSC. The second group of factors are produced primarily by activated T cells and tumor stroma and directly activate MDSC. These factors, which include IFN gamma, IL-13, IL-4 and TGFβ, among others, activate several different signaling pathways in MDSCs that involve STAT6, STAT1, and NF-kB. Most studies have shown that the immune-suppressive function of MDSCs requires direct cell–cell contact, which indicates that they operate either through cell-surface receptors and/or through the release of short-lived soluble mediators. Currently, a number of clinical trials explores the possibility of regulating immune responses in cancer by depleting ot inactivating MDSC in cancer patients. DisclosuresNo relevant conflicts of interest to declare.

Myeloid‐derived suppressor cell activation by combined LPS and IFN‐γ treatment impairs DC development

Myeloid-derived suppressor cells (MDSC) and DC are major controllers of immune responses against tumors or infections. However, it remains unclear how DC development and MDSC suppressor activity both generated from myeloid precursor cells are regulated. Here, we show that the combined treatment of BM-derived MDSC with LPS plus IFN-gamma inhibited the DC development but enhanced MDSC functions, such as NO release and T-cell suppression. This was not observed by the single treatments in vitro. In the spleens of healthy mice, we identified two Gr-1(low)CD11b(high)Ly-6C(high)SSC(low)Mo-MDSC and Gr-1(high)CD11b(low)PMN-MDSC populations with suppressive potential, whereas Gr-1(high)CD11b(high) neutrophils and Gr-1(low)CD11b(high)SSC(low) eosinophils were not suppressive. Injections of LPS plus IFN-gamma expanded these populations within the spleen but not LN leading to the block of the proliferation of CD8(+) T cells. At the same time, their capacity to develop into DC was impaired. Together, our data suggest that spleens of healthy mice contain two subsets of MDSC with suppressive potential. A two-signal-program through combined LPS and IFN-gamma treatment expands and fully activates MDSC in vitro and in vivo.

The effect of alcohol septal ablation on B-type natriuretic peptide in patients with hypertrophic obstructive cardiomyopathy

A t(8;21)(q22;q22) without blood and bone marrow invasion by immature myeloid precursor cells occurred in a patient previously treated for polycythemia vera. The presence of a molecular rearrangement confirmed that the chromosomal abnormality was identical to that observed in acute leukemia with t(8;21). This case shows that the translocation, t(8;21), may occur in myelodysplasia and suggests that it can precede the appearance of overt leukemia.

Acute lymphoplasmacytoid dendritic cell (DC2) leukemia: Results from the Hellenic Dendritic Cell Leukemia Study Group

We present a cohort of 22 patients with type 2 dendritic cell (DC2) acute leukemia (or blastic plasmacytoid dendritic cell neoplasm-BPDCN, as it has been recently named), diagnosed in Greece over the past 12-year period, according to the main clinical and immunophenotypic features of this entity. Four additional cases are discussed, classified as leukemia of ambiguous lineage (LAL), because of the simultaneous detection of a CD56 negative DC2 population and of a second myeloid precursor cell population. The morphological features and cytogenetic findings of the typical BPDCN cases were similar to those previously described. Acute lymphoblastic leukemia-type chemotherapeutic regimens were more efficient in controlling the disease. Immunophenotyping of typical BPDCN cases revealed CD4 +, CD56 +, HLA-DR + and CD123 bright neoplastic cells, in the absence of major B-, T- and myeloid-associated markers, while the phenotype of the four cases characterized as LAL highlights the risk of misdiagnosis. Based on our experience, we propose a flow cytometric algorithmic approach for the distinction of typical BPDCN from certain types of acute myeloid leukemia, but also for the identification of acute myeloid leukemia, admixed with CD56 negative DC2 cells, which could be misdiagnosed as BPDCN.

Cooperation between PU.1 and CAAT/Enhancer-binding Protein β Is Necessary to Induce the Expression of the MD-2 Gene

Myeloid differentiation factor 2 (MD-2) binds Gram-negative bacterial lipopolysaccharide with high affinity and is essential for Toll-like receptor 4-dependent signal transduction. MD-2 has recently been recognized as a type II acute phase protein. Plasma concentrations of the soluble form of MD-2 increase markedly during the course of severe infections. Its production is regulated in hepatocytes and myeloid cells by interleukin-6 (IL-6) but not IL-1beta. In the present work we show that two transcription factors (TF), PU.1 and CAAT/enhancer-binding protein beta (C/EBPbeta), participate in the activation of the human MD-2 gene in hepatocytic cells after stimulation with IL-6. PU.1 TF and proximal PU.1 binding sites in the MD-2 promoter were shown to be critical for the basal activity of the promoter as well as for IL-6-induced soluble MD-2 production. Deletions of proximal portions of the MD-2 promoter containing PU.1 and/or NF-IL-6 consensus binding sites as well as site-directed mutagenesis of these binding sites abrogated IL-6-dependent MD-2 gene activation. We show that the cooperation between C/EBPbeta and PU.1 is critical for the transcriptional activation of the MD-2 gene by IL-6. PU.1 was essentially known as a TF involved in the differentiation of myeloid precursor cells and the expression of surface receptors of the innate immunity. Herein, we show that it also participates in the regulation of an acute phase protein, MD-2, in nonmyeloid cells cooperatively with C/EBPbeta, a classical IL-6-inducible TF.

Complexity of CEBPA Dysregulation in Human Acute Myeloid Leukemia

The transcription factor CCAAT enhancer binding protein alpha (CEBPA) is crucial for normal development of granulocytes. Various mechanisms have been identified how CEBPA function is dysregulated in patients with acute myeloid leukemia (AML). In particular, dominant-negative mutations located either at the N- or the C terminus of the CEBPA gene are observed in roughly 10% of AML patients, either in the combination on separate alleles or as sole mutation. Clinically significant complexity exists among AML with CEBPA mutations, and patients with double CEBPA mutations seem to have a more favorable course of the disease than patients with a single mutation. In addition, myeloid precursor cells of healthy carriers with a single germ-line CEBPA mutation evolve to overt AML by acquiring a second sporadic CEBPA mutation. This review summarizes recent reports on dysregulation of CEBPA function at various levels in human AML and therapeutic concepts targeting correction of CEBPA activity. The currently available data are persuasive evidence that impaired CEBPA function contributes directly to the development of AML, whereas restoring CEBPA function represents a promising target for novel therapeutic strategies in AML.

Anchored and soluble gangliosides contribute to myelosupportivity of stromal cells

Stroma-mediated myelopoiesis depends upon growth factors and an appropriate intercellular microenvironment. Previous studies have demonstrated that gangliosides, produced by hepatic stromal cell types, are required for optimal myelosupportive function. Here, we compared the mielossuportive functions of a bone marrow stroma (S17) and skin fibroblasts (SF) regarding their ganglioside pattern of synthesis and shedding. The survival and proliferation of a myeloid precursor cell (FDC-P1) were used as reporter. Although the ganglioside synthesis of the two stromal cells was similar, their relative content and shedding were distinct. The ganglioside requirement for mielossuportive function was confirmed by the decreased proliferation of FDC-P1 cells in ganglioside synthesis-inhibited cultures and in presence of an antibody to GM3 ganglioside. The distinct mielossuportive activities of the S17 and SF stromata may be related to differences on plasma membrane ganglioside concentrations or to differences on the gangliosides shed and their subsequent uptake by myeloid cells, specially, GM3 ganglioside.

Impaired osteoclastogenesis by staphylococcal lipoteichoic acid through Toll-like receptor 2 with partial involvement of MyD88

Degenerative bone disease, marked by excessive loss of calcified matrix, is often associated with bacterial infections. Osteoclasts, which mediate the bone-resorptive process, are derived mainly from myeloid precursor cells of the monocyte/macrophage lineage, from which cells with phagocytic and inflammatory capacities may alternatively arise. Here, we investigated the effect of LTA, a major cell-wall virulence factor of Gram-positive bacteria, on osteoclast differentiation. Osteoclast precursors were prepared from C57BL/6 mouse BM using M-CSF and RANKL. When osteoclastogenesis was induced in the presence of staphylococcal LTA, LTA dose-dependently inhibited the differentiation of osteoclast precursors to mature osteoclasts. A corresponding inhibition of bone-resorptive function was observed in the reduced resorption area on calcium phosphate-coated culture plates. In contrast, the phagocytic and inflammatory potential of the osteoclast precursors increased in the presence of LTA. TLR2, known to recognize LTA, might be essential for the LTA inhibition of osteoclastogenesis, as the inhibition did not occur in the precursors from TLR2-deficient mice. Importantly, MyD88-dependent and MyD88-independent pathways would participate in the inhibition, as determined using MyD88-deficient cells. Moreover, LTA inhibited phosphorylation of ERK and JNK in osteoclast precursors stimulated with M-CSF and RANKL, concomitantly with a decreased DNA-binding activity of AP-1. These results suggest that staphylococcal LTA inhibits osteoclast differentiation primarily through TLR2 but also in part through MyD88 signaling, which in turn, inhibits activation of ERK, JNK, and AP-1.