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Activation Motif (activation + motif)

Distribution by Scientific Domains

Medical Sciences	100%

Selected Abstracts

Increased TLR responses in dendritic cells lacking the ITAM-containing adapters DAP12 and FcR,

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 1 2008
Ching-Liang Chu Dr.
Abstract The inhibitory effect of DAP12 on macrophages has been revealed by examining myeloid cells from DAP12-deficient mice. In this report, we demonstrate that both DAP12 and the Fc,RI,-chain (FcR,) are required for negative regulation of TLR responses in bone marrow-derived dendritic cells (DC). Loss of both DAP12 and FcR, enhanced the pro-inflammatory cytokine production and maturation of DC after TLR stimulation, resulting in a greater percentage of DC that produced IL-12 p40, TNF, and IL-6, and expressed high levels of MHC class II, CD80, and CD86. Whereas DC lacking only DAP12 showed some increased TLR responses, those lacking only FcR, had a greater enhancement of maturation and cytokine production, though to a lesser extent than DC lacking both DAP12 and FcR,. Additionally, antigen-specific T cell proliferation was enhanced by DAP12,/,FcR,,/, DC relative to wild-type DC after maturation. Similar to DAP12,/,FcR,,/, DC, Syk-deficient DC also had increased inflammatory cytokine production, maturation, and antigen presentation. These results confirm the inhibitory effect of immunoreceptor tyrosine-based activation motif (ITAM) signaling in myeloid cells and show that DC and macrophages differ in their dependence on the ITAM-containing adapters DAP12 and FcR, for negative regulation of TLR signaling. [source]

Activating and inhibitory nature of the murine paired immunoglobulin-like receptor family

IMMUNOLOGICAL REVIEWS, Issue 1 2001
Toshiyuki Takai
Summary: Clones for murine paired immunoglobulin-like receptors (PIR) were first isolated as those coding for type I transmembrane glycoproteins with six immunoglobulin-like domains homologous to human Fc,R, bovine Fc,2R, and other related receptors. However, they turned out to bind neither IgA nor other immunoglobulins in the case of the ectopic expression on COS-1 fibroblastic cells. PIR-A and B are expressed on a wide variety of cells in the murine immune system, such as in B cells, mast cells, macrophages, and dendritic cells, mostly in a pairwise fashion. PIR-A requires homodimeric Fc receptor common , chain, which harbors an immunoreceptor tyrosine-based activation motif, for its efficient cell surface expression and for the delivery of activation signaling. In contrast, PIR-B contains immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in its cytoplasmic portion and inhibits receptor-mediated activation signaling in vitro upon engagement with other activating-type receptors such as the antigen receptor on B cells and the high affinity Fc receptor for IgE on mast cells. ITIMs of PIR-B on macrophages and B cells have been shown to be constitutively phosphorylated in their tyrosine residues. Although the ligand for PIR still remains unknown, the transgenics and the gene-targeted mice will provide us with valuable information on their physiological roles in the immune regulation. We thank Hiromi Kubagawa for discussion. This work is supported by CREST Program of JST, Virtual Research Institute of Aging funded by Boehringer Ingelheim, and by research grants from the Ministry of Education, Science, Sports and Culture of Japan to T. Takai. [source]

Collagen promotes sustained glycoprotein VI signaling in platelets and cell lines

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 11 2007
M. G. TOMLINSON
Summary. Background:,Glycoprotein (GP)VI is the major signaling receptor for collagen on platelets and signals via the associated FcR,-chain, which has an immunoreceptor tyrosine-containing activation motif (ITAM). Objective:,To determine why GPVI,FcR, signals poorly, or not at all, in response to collagen in hematopoietic cell lines, despite robust responses to the GPVI-reactive snake venom toxin convulxin. Methods and results:,Using a nuclear factor of activated T-cells (NFAT) transcriptional reporter assay, a sensitive readout for sustained ITAM signaling, we demonstrate collagen-induced GPVI,FcR, signaling in hematopoietic cell lines. This is accompanied by relatively weak but sustained protein tyrosine phosphorylation, in contrast to the stronger but transient response to convulxin. Sustained signaling by collagen is also observed in platelets and is necessary for the maintenance of spreading on collagen. Finally, in cell lines, the inhibitory collagen receptor leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1), which is not expressed on platelets but is present on most hematopoietic cells, inhibits GPVI responses to collagen but not convulxin. Conclusion:,The inability of previous studies to readily detect GPVI collagen signaling in cell lines is probably because of the weak but sustained nature of the signal and the presence of the inhibitory collagen receptor LAIR-1. In platelets, we propose that GPVI,FcR, has evolved to transmit sustained signals in order to maintain spreading over several hours, as well as facilitating rapid activation through release of feedback agonists and integrin activation. The establishment of a cell line NFAT assay will facilitate the molecular dissection of GPVI signaling and the identification of GPVI antagonists in drug discovery. [source]

Interleukin-27 inhibits human osteoclastogenesis by abrogating RANKL-mediated induction of nuclear factor of activated T cells c1 and suppressing proximal RANK signaling

ARTHRITIS & RHEUMATISM, Issue 2 2010
George D. Kalliolias
Objective Interleukin-27 (IL-27) has stimulatory and regulatory immune functions and is expressed in rheumatoid arthritis (RA) synovium. This study was undertaken to investigate the effects of IL-27 on human osteoclastogenesis, to determine whether IL-27 can stimulate or attenuate the osteoclast-mediated bone resorption that is a hallmark of RA. Methods Osteoclasts were generated from blood-derived human CD14+ cells. The effects of IL-27 on osteoclast formation were evaluated by counting the number of tartrate-resistant acid phosphatase,positive multinucleated cells and measuring the expression of osteoclast-related genes. The induction of nuclear factor of activated T cells c1 (NFATc1) and the activation of signaling pathways downstream of RANK were measured by immunoblotting. The expression of key molecules implicated in osteoclastogenesis (NFATc1, RANK, costimulatory receptors, and immunoreceptor tyrosine,based activation motif,harboring adaptor proteins) was measured by real-time reverse transcription,polymerase chain reaction. Murine osteoclast precursors obtained from mouse bone marrow and synovial fluid macrophages derived from RA patients were also tested for their responsiveness to IL-27. Results IL-27 inhibited human osteoclastogenesis, suppressed the induction of NFATc1, down-regulated the expression of RANK and triggering receptor expressed on myeloid cells 2 (TREM-2), and inhibited RANKL-mediated activation of ERK, p38, and NF-,B in osteoclast precursors. Synovial fluid macrophages from RA patients were refractory to the effects of IL-27. In contrast to the findings in humans, IL-27 only moderately suppressed murine osteoclastogenesis, and this was likely attributable to low expression of the IL-27 receptor subunit WSX-1 on murine osteoclast precursors. Conclusion IL-27 inhibits human osteoclastogenesis by a direct mechanism that suppresses the responses of osteoclast precursors to RANKL. These findings suggest that, in addition to its well-known antiinflammatory effects, IL-27 plays a homeostatic role in restraining bone erosion. This homeostatic function is compromised under conditions of chronic inflammation such as in RA synovitis. [source]

Compromised ITAM-based platelet receptor function in a patient with immune thrombocytopenic purpura

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 7 2008
E. E. GARDINER
Summary.,Background:,Receptors on platelets that contain immunoreceptor tyrosine-based activation motifs (ITAMs) include collagen receptor glycoprotein (GP) VI, and Fc,RIIa, a low affinity receptor for immunoglobulin (Ig) G. Objectives:,We examined the function of GPVI and Fc,RIIa in a patient diagnosed with immune thrombocytopenic purpura (ITP) who had unexplained pathological bruising despite normalization of the platelet count with treatment. Methods and Results:,Patient platelets aggregated normally in response to ADP, arachadonic acid and epinephrine, but not to GPVI agonists, collagen or collagen-related peptide, or to Fc,RII-activating monoclonal antibody (mAb) 8.26, suggesting ITAM receptor dysfunction. Plasma contained an anti-GPVI antibody by MAIPA and aggregated normal platelets. Aggregating activity was partially (,60%) blocked by Fc,RIIa-blocking antibody, IV.3, and completely blocked by soluble GPVI ectodomain. Full-length GPVI on the patient platelet surface was reduced to ,10% of normal levels, and a ,10-kDa GPVI cytoplasmic tail remnant and cleaved Fc,RIIa were detectable by western blot, indicating platelet receptor proteolysis. Plasma from the patient contained ,150 ng mL,1 soluble GPVI by ELISA (normal plasma, ,15 ng mL,1) and IgG purified from patient plasma caused Fc,RIIa-mediated, EDTA-sensitive cleavage of both GPVI and Fc,RIIa on normal platelets. Conclusions:,In ITP patients, platelet autoantibodies can curtail platelet receptor function. Platelet ITAM receptor dysfunction may contribute to the increased bleeding phenotype observed in some patients with ITP. [source]