Toll-like receptor 4-mediated signaling regulates IL-7-driven proliferation and differentiation of B-cell precursors

von Willebrand factor links primary hemostasis to innate immunity

The plasma multimeric glycoprotein von Willebrand factor (VWF) plays a critical role in primary hemostasis by tethering platelets to exposed collagen at sites of vascular injury. Recent studies have identified additional biological roles for VWF, and in particular suggest that VWF may play an important role in regulating inflammatory responses. However, the molecular mechanisms through which VWF exerts its immuno-modulatory effects remain poorly understood. In this study, we report that VWF binding to macrophages triggers downstream MAP kinase signaling, NF-κB activation and production of pro-inflammatory cytokines and chemokines. In addition, VWF binding also drives macrophage M1 polarization and shifts macrophage metabolism towards glycolysis in a p38-dependent manner. Cumulatively, our findings define an important biological role for VWF in modulating macrophage function, and thereby establish a novel link between primary hemostasis and innate immunity.

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

Toll-like receptor 4 (TLR4) is a pattern-recognizing receptor that can bind exogenous and endogenous ligands. It is expressed by acute myeloid leukemia (AML) cells, several bone marrow stromal cells, and nonleukemic cells involved in inflammation. TLR4 can bind a wide range of endogenous ligands that are present in the bone marrow microenvironment. Furthermore, the TLR4-expressing nonleukemic bone marrow cells include various mesenchymal cells, endothelial cells, differentiated myeloid cells, and inflammatory/immunocompetent cells. Osteoblasts are important stem cell supporting cells localized to the stem cell niches, and they support the proliferation and survival of primary AML cells. These supporting effects are mediated by the bidirectional crosstalk between AML cells and supportive osteoblasts through the local cytokine network. Finally, TLR4 is also important for the defense against complicating infections in neutropenic patients, and it seems to be involved in the regulation of inflammatory and immunological reactions in patients treated with allogeneic stem cell transplantation. Thus, TLR4 has direct effects on primary AML cells, and it has indirect effects on the leukemic cells through modulation of their supporting neighboring bone marrow stromal cells (i.e., modulation of stem cell niches, regulation of angiogenesis). Furthermore, in allotransplant recipients TLR4 can modulate inflammatory and potentially antileukemic immune reactivity. The use of TLR4 targeting as an antileukemic treatment will therefore depend both on the biology of the AML cells, the biological context of the AML cells, aging effects reflected both in the AML and the stromal cells and the additional antileukemic treatment combined with HSP90 inhibition.

Signal-transducing adaptor protein-1 and protein-2 in hematopoiesis and diseases

Inflammatory and immune signals are involved in stressed hematopoiesis under myeloablation, infection, chronic inflammation, and aging. These signals also affect malignant pathogenesis, and the dysregulated immune environment which causes the resistance to treatment. On activation, various types of protein tyrosine kinases in the cytoplasm mediate the cascade, leading to the transcription of target genes in the nucleus. Adaptor molecules are commonly defined as proteins that lack enzymatic activity, DNA-binding or receptor functions and possess protein-protein or protein-lipid interaction domains. By binding to specific domains of signaling molecules, adaptor proteins adjust the signaling responses after the ligation of receptors of soluble factors, including cytokines, chemokines, and growth factors, as well as pattern recognition receptors such as toll-like receptors. The signal-transducing adaptor protein (STAP) family regulates various intracellular signaling pathways. These proteins have a pleckstrin homology domain in the N-terminal region and an SRC-homology 2-like domain in the central region, representing typical binding structures as adapter proteins. Following the elucidation of the effects of STAPs on terminally differentiated immune cells, such as macrophages, T cells, mast cells, and basophils, recent findings have indicated the critical roles of STAP-2 in B-cell progenitor cells in marrow under hematopoietic stress and STAP-1 and -2 in BCR-ABL-transduced leukemogenesis. In this review, we focus on the role of STAPs in the bone marrow.

Signal-transducing adaptor protein-2 delays recovery of B lineage lymphocytes during hematopoietic stress

Signal-transducing adaptor protein-2 (STAP-2) was discovered as a C-FMS/M-CSFR interacting protein and subsequently found to function as an adaptor of signaling or transcription factors. These include STAT5, MyD88 and IB kinase in macrophages, mast cells, and T cells. There is additional information about roles for STAP-2 in several types of malignant diseases including chronic myeloid leukemia; however, none have been reported concerning B-lineage lymphocytes. We have now exploited gene targeted and transgenic mice to address this lack of knowledge, and demonstrated that STAP-2 is not required under normal, steadystate conditions. However, recovery of B cells following transplantation was augmented in the absence of STAP-2. This appeared to be restricted to cells of B-cell lineage with myeloid rebound noted as unremarkable. Furthermore, all hematologic parameters were observed to be normal once recovery from transplantation was complete. In addition, overexpression of STAP-2, specifically in lymphoid cells, resulted in reduced numbers of latestage B-cell progenitors within the bone marrow. While numbers of mature peripheral B and T cells were unaffected, recovery from sub-lethal irradiation or transplantation was dramatically reduced. Lipopolysaccharide (LPS) normally suppresses B precursor expansion in response to interleukin 7; however, STAP-2 deficiency made these cells more resistant. Preliminary RNA-sequencing analyses indicated multiple signaling pathways in B progenitors to be STAP-2-dependent. These findings suggest that STAP-2 modulates formation of B lymphocytes in demand conditions. Further study of this adapter protein could reveal ways to speed recovery of humoral immunity following chemotherapy or transplantation.

The activation of Toll-like receptor 4 reverses tumor differentiation in human glioma U251 cells via Notch pathway

Toll-like receptors (TLRs) are closely related to cancer. However, the mechanism for TLR regulation of cancer is not fully understood. Our previous studies demonstrated that toll-like receptor (TLR) 4 functions to maintain the un-differential stem cell phenotypes of human endothelial progenitor cells. In this study, we found that human glioma cells expressed several TLRs. The activation of TLR4 by LPS in glioma U251 cells induced the expression of cytokines, including IL-1β, IL-6, IL-8, and TNFα, suggesting the functional expression of TLR4. Nude mouse in vivo studies showed that LPS treatment promoted tumor growth, and decreased mouse survival. But LPS treatment did not promote tumor cell proliferation in vitro. Meanwhile, we found that LPS treatment down-regulated the expression of glial fibrillary acidic protein (GFAP), an important differentiation maker of glioma, at both mRNA and protein levels. TLR4 activation also down-regulated GFAP in glioma Hs683 cells. LPS did not induce the activation of MAPKs, but induced the activation of NF-κB. However, pharmacological inhibition of NF-κB signaling did not reverse the down-regulation of GFAP. Furthermore, we found that LPS induced the activation of Notch pathway, which was MyD88-dependent, and Notch inhibition reversed the down-regulation of GFAP. In addition, LPS treatment up-regulated stem cell makers, including CD34 and CD133. Taken together, these results suggested that in human glioma U251 cells, TLR4 functions to reverse tumor differentiation, and it may be a target for glioma prevention and therapy.

The Role of TLR4 on B Cell Activation and Anti-2GPI Antibody Production in the Antiphospholipid Syndrome

High titer of anti-β₂-glycoprotein I antibodies (anti-β₂GPI Ab) plays a pathogenic role in antiphospholipid syndrome (APS). Numerous studies have focused on the pathological mechanism in APS; however, little attention is paid to the immune mechanism of production of anti-β₂GPI antibodies in APS. Our previous study demonstrated that Toll-like receptor 4 (TLR4) plays a vital role in the maturation of bone marrow-derived dendritic cells (BMDCs) from the mice immunized with human β₂-glycoprotein I (β₂GPI). TLR4 is required for the activation of B cells and the production of autoantibody in mice treated with β₂GPI. However, TLR4 provides a third signal for B cell activation and then promotes B cells better receiving signals from both B cell antigen receptor (BCR) and CD40, thus promoting B cell activation, surface molecules expression, anti-β₂GPI Ab production, and cytokines secretion and making B cell functioning like an antigen presenting cell (APC). At the same time, TLR4 also promotes B cells producing antibodies by upregulating the expression of B-cell activating factor (BAFF). In this paper, we aim to review the functions of TLR4 in B cell immune response and antibody production in autoimmune disease APS and try to find a new way for the prevention and treatment of APS.

Identification and characterisation of the immune response properties of Lampetra japonica BLNK

B cell linker protein (BLNK) is a central linker protein involved in B cell signal transduction in jawed vertebrates. In a previous study, we have reported the identification of a BLNK homolog named Lj-BLNK in lampreys. In this study, a 336 bp cDNA fragment encoding the Lj-BLNK Src homology 2 (SH2) domain was cloned into the vector pET-28a(+) and overexpressed in Escherichia coli BL21. The recombinant fragment of Lj-BLNK (rLj-BLNK) was purifiedby His-Bind affinity chromatography, and polyclonal antibodies against rLj-BLNK were raised in male New Zealand rabbits. Fluorescenceactivated cell sorting (FACS) analysisrevealed that Lj-BLNK was expressed in approximately 48% of the lymphocyte-like cells of control lampreys, and a significant increase in Lj-BLNK expression was observed in lampreys stimulated with lipopolysaccharide (LPS). Western blotting analysis showed that variable lymphocyte receptor B (VLRB) and Lj-BLNKwere distributed in the same immune-relevant tissues, and the levels of both were upregulated in supraneural myeloid bodies and lymphocyte-like cells after LPS stimulation. Immunofluorescence demonstrated that Lj-BLNK was localized in VLRB(+) lymphocyte-like cells. These results indicate that the Lj-BLNK protein identified in lampreys might play an important role in the VLRB-mediated adaptive immune response.