Biomedical subjects

Graciela Andonegui

Publications and source records attributed to Graciela Andonegui.

8 recordsLinked to original sources

PubMed2005

Platelets express functional Toll-like receptor-4.

Profound thrombocytopenia occurs in humans with sepsis and in mice administered lipopolysaccharide (LPS). Growing evidence indicates that platelets may contribute to these abnormalities, but whether that is a direct result of LPS activation of platelets or an indirect result of other inflammatory mechanisms remains unclear. Here we demonstrate that although platelets do not increase P-selectin expression in response to LPS, platelets bind more avidly to fibrinogen under flow conditions in a Toll-like receptor-4 (TLR4)-dependent manner. In addition, we find that CD41+ megakaryocytes grown from fetal livers and adult circulating platelets express significant amounts of TLR4. LPS induced thrombocytopenia in wild-type mice but not in TLR4-deficient (TLR4def) mice. Wild-type platelets accumulated in the lungs of wild-type mice in response to LPS; TLR4def platelets did not. However, wild-type platelets did not accumulate in the lungs of LPS-treated TLR4def mice. Neutrophils also accumulated in the lungs, and this preceded platelet accumulation. Neutrophil depletion completely abolished LPS-induced platelet sequestration into the lungs, but platelet depletion did not affect neutrophil accumulation. Thus, our data show for the first time that platelets do express functional levels of TLR4, which contribute to thrombocytopenia through neutrophil-dependent pulmonary sequestration in response to LPS.

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PubMed2004

Role of CD44 and hyaluronan in neutrophil recruitment.

Lymphocyte CD44 interactions with hyaluronan localized on the endothelium have been demonstrated to mediate rolling and regulate lymphocyte entry into sites of chronic inflammation. Because neutrophils also express CD44, we investigated the role of CD44 and hyaluronan in the multistep process of neutrophil recruitment. CD44(-/-) and wild-type control mice were intrascrotally injected with the neutrophil-activating chemokine, MIP-2, and leukocyte kinetics in the cremasteric microcirculation were investigated 4 h subsequently using intravital microscopy. Neither the rolling flux nor the rolling velocities were decreased in CD44(-/-) mice relative to wild-type mice. In vitro, neutrophils did not roll on the CD44 ligand hyaluronan, consistent with the in vivo data that CD44/hyaluronan did not mediate rolling. However, the number of adherent leukocytes in the venule was decreased by 65% in CD44(-/-) mice compared with wild-type mice. Leukocyte emigration was also greatly decreased in the CD44(-/-) mice. The same decrease in adhesion and emigration was observed in the wild-type mice given hyaluronidase. Histology revealed neutrophils as being the dominant infiltrating population. We generated chimeric mice that express CD44 either on their leukocytes or on their endothelium and found that CD44 on both the endothelium and neutrophils was important for optimal leukocyte recruitment into tissues. Of those neutrophils that emigrated in wild-type and CD44(-/-) mice, there was no impairment in migration through the interstitium. This study suggests that CD44 can mediate some neutrophil adhesion and emigration, but does not appear to affect subsequent migration within tissues.

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PubMed2004

TLR4 contributes to disease-inducing mechanisms resulting in central nervous system autoimmune disease.

Environmental factors strongly influence the development of autoimmune diseases, including multiple sclerosis. Despite this clear association, the mechanisms through which environment mediates its effects on disease are poorly understood. Pertussis toxin (PTX) functions as a surrogate for environmental factors to induce animal models of autoimmunity, such as experimental autoimmune encephalomyelitis. Although very little is known about the molecular mechanisms behind its function in disease development, PTX has been hypothesized to facilitate immune cell entry to the CNS by increasing permeability across the blood-brain barrier. Using intravital microscopy of the murine cerebromicrovasculature, we demonstrate that PTX alone induces the recruitment of leukocytes and of active T cells to the CNS. P-selectin expression was induced by PTX, and leukocyte/endothelial interactions could be blocked with a P-selectin-blocking Ab. P-selectin blockade also prevented PTX-induced increase in permeability across the blood-brain barrier. Therefore, permeability is a secondary result of recruitment, rather than the primary mechanism by which PTX induces disease. Most importantly, we show that PTX induces intracellular signals through TLR4, a receptor intimately associated with innate immune mechanisms. We demonstrate that PTX-induced leukocyte recruitment is dependent on TLR4 and give evidence that the disease-inducing mechanisms initiated by PTX are also at least partly dependent on TLR4. We propose that this innate immune pathway is a novel mechanism through which environment can initiate autoimmune disease of the CNS.

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PubMed2004

A down-regulatable E-selectin ligand is functionally important for PSGL-1-independent leukocyte-endothelial cell interactions.

P-selectin glycoprotein-1 (PSGL-1) supports P-selectin-dependent rolling in vivo and in vitro. However, controversy exists regarding the importance of PSGL-1-dependent and -independent E-selectin rolling. Using antibodies against PSGL-1 and PSGL-1(-/-) mice, we demonstrated abolition of P-selectin-dependent rolling but only partial inhibition of E-selectin-mediated rolling in the cremaster microcirculation following local administration of tumor necrosis factor alpha (TNF-alpha). In vitro studies demonstrated that binding of recombinant mouse E-selectin chimera to PSGL-1(-/-) neutrophils was dramatically decreased in mice treated systemically but not locally with TNF-alpha. Further, PSGL-1 blockade abolished E-selectin-dependent rolling in wild-type mice following systemic TNF-alpha administration but not local TNF-alpha administration. Together, these data support an E-selectin ligand present on PSGL-1(-/-) neutrophils that is down-regulatable upon systemic but not local activation. To determine whether the PSGL-1-independent E-selectin ligand was physiologically important, we used a P- and E-selectin-dependent cutaneous contact hypersensitivity model. Binding studies showed no E-selectin ligand down-regulation in this model. The few cells that rolled on E-selectin ligand following PSGL-1 antibody administration or in PSGL-1 deficiency were sufficient to induce profound contact hypersensitivity. In conclusion, E-selectin mediates PSGL-1-dependent and independent rolling and the latter can be down-regulated by systemic activation and can replace PSGL-1 to support the development of inflammation.

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PubMed2003

Endothelium-derived Toll-like receptor-4 is the key molecule in LPS-induced neutrophil sequestration into lungs.

The rapid and selective accumulation of neutrophils into the lungs is thought to underlie the pulmonary failure that leads to sepsis-related death. In this study we investigated whether neutrophil TLR4 is important in LPS-induced pulmonary neutrophil recruitment by creating chimeric mice (transferring bone marrow between TLR4(+/+) and TLR4(-/-) mice). In TLR4(+/+) mice receiving TLR4(-/-) bone marrow, 6 weeks after transplant TLR4 was absent in all circulating leukocytes as well as in resident macrophages (these mice were termed LeukocyteTLR4(-/-)), and these cells were completely nonresponsive to LPS. In TLR4(-/-) mice receiving TLR4(+/+) bone marrow, endothelial cells but not leukocytes were deficient in TLR4 (EndotheliumTLR4(-/-)). Surprisingly, systemic LPS (0.5 mg/kg) induced a dramatic increase in neutrophil sequestration into the lungs of LeukocyteTLR4(-/-) mice over the first 4 hours. Concomitantly, numbers of circulating leukocytes decreased by 90%. By contrast, EndotheliumTLR4(-/-) mice showed very little increase in neutrophil sequestration in the lungs, suggesting that endothelium rather than leukocyte TLR4 was important. Intravital microscopy of peripheral microcirculation in the cremaster muscle revealed about 30-fold more leukocyte-endothelial cell interactions in LPS-treated EndotheliumTLR4(-/-) mice than in LPS-treated LeukocyteTLR4(-/-) mice. This is consistent with less sequestration of leukocytes into the lungs of EndotheliumTLR4(-/-) mice. In conclusion, our data challenge the view that LPS directly activates neutrophils to trap in lungs and suggest a far more important role than previously appreciated for the endothelial cells.

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PubMed2002

Lipopolysaccharide-induced leukocyte-endothelial cell interactions: a role for CD14 versus toll-like receptor 4 within microvessels.

The objective of this study was to systematically assess leukocyte-endothelial cell interactions in vivo in response to LPS in CD14-deficient (CD14(-/-)) and Toll-like receptor 4-deficient (TLR4(d); C3H/HeJ) mice. Local injection of LPS (0.05 micro g/kg) into muscle at a concentration that did not cause systemic effects produced a significant reduction in the speed with which leukocytes roll and a substantial increase in leukocyte adhesion and emigration 4 h postinjection. There was no response to LPS in the muscle microvasculature of CD14(-/-) mice or TLR4(d) animals. Systemic LPS induced leukopenia and significant sequestration of neutrophils in lungs in wild-type mice but not in CD14(-/-) or TLR4(d) mice. P-selectin expression was examined in numerous mouse organs using a dual radiolabeling mAb technique. The results revealed a 20- to 50-fold increase in P-selectin expression in response to LPS in all wild-type tissues examined but no response in any TLR4(d) tissues. Surprisingly, there was consistently a partial, significant increase in P-selectin expression in numerous microvasculatures including skin and pancreas, but no increase in P-selectin was detected in lung, muscle, and other organs in CD14(-/-) mice in response to LPS. Next, the skin and muscle microcirculation were visualized using intravital microscopy after systemic LPS treatment, and the results confirmed a CD14-independent mechanism of leukocyte sequestration in skin but not muscle. In summary, our results suggest that the LPS-induced leukocyte sequestration to some tissues is entirely dependent on both CD14 and TLR4 but there are CD14-independent, TLR4-dependent endothelial cell responses in some microvascular beds.

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PubMed2002

Profound differences in leukocyte-endothelial cell responses to lipopolysaccharide versus lipoteichoic acid.

We have investigated the effects of LPS from Escherichia coli, lipoteichoic acid (LTA), and peptidoglycan (PepG) from Staphylococcus aureus, and live S. aureus on leukocyte-endothelial interactions in vivo using intravital microscopy to visualize muscle microvasculature. Systemic vs local administration of LPS induced very different responses. Local administration of LPS into muscle induced significant leukocyte rolling, adhesion, and emigration in postcapillary venules at the site of injection. LPS given systemically dramatically dropped circulating leukocyte counts and increased neutrophils in the lung. However, the drop in circulating leukocytes was not associated with leukocyte sequestration to the site of injection (peritoneum) nor to peripheral microvessels in muscles. Unlike LPS, various preparations of LTA had no systemic and very minor local effect on leukocyte-endothelial interactions, even at high doses and for prolonged duration. LPS, but not LTA, potently activated human endothelium to recruit leukocytes under flow conditions in vitro. Endothelial adhesion molecule expression was also increased extensively with LPS, but not LTA. Interestingly, systemic administration of live S. aureus induced leukocyte-endothelial cell responses similar to LPS. PepG was able to induce leukocyte-endothelial interactions in muscle and peritoneum, but had no effect systemically (no increase in neutrophils in lungs and no decrease in circulating neutrophil counts). These results demonstrate that: 1) LPS has potent, but divergent local and systemic effects on leukocyte-endothelial interactions; 2) S. aureus can induce a systemic response similar to LPS, but this response is unlikely to be due to LTA, but more likely to be mediated in part by PepG.

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PubMedDate not supplied

Lipopolysaccharide: a p38 MAPK-dependent disrupter of neutrophil chemotaxis.

In sepsis, and in models of sepsis including endotoxemia, impaired neutrophil recruitment and chemotaxis have been reported. The inability of the endotoxemic neutrophil to chemotax could be attributed to the fact that intracellular signaling via LPS overrides signals from endogenous chemokines or, alternatively, that sequestration of neutrophils into lungs prevents access to peripheral tissues. Using both in vitro and in vivo chemotaxis assays the authors established that neutrophils from healthy mice chemotaxed in vivo toward MIP-2, whereas endotoxemic neutrophils did not. Since LPS activates leukocytes via the p38 MAPK pathway, SKF86002, a p38 MAPK inhibitor, was given to endotoxemic animals. SKF86002 significantly reversed the LPS-induced impairment in emigration of endotoxic neutrophils in response to MIP-2. Neutrophil chemotaxis in vitro was also impaired by LPS, via a p38 MAPK-dependent pathway, and this impairment could be reversed via p38 MAPK inhibition. Although neutrophil numbers dropped in the circulation and trapped in lungs during endotoxemia, SKF86002 did not reverse these parameters, demonstrating that p38 MAPK inhibition did not release trapped neutrophils from the lungs. In conclusion, the data suggest that the impaired emigration and chemotaxis of neutrophils at peripheral sites during endotoxemia may be partially due to a p38 MAPK-mediated inhibition of neutrophil responses to endogenous chemokines.

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