Biomedical subjects

Mikael J Pittet

Publications and source records attributed to Mikael J Pittet.

6 recordsLinked to original sources

PubMed2007

Ly-6Chi monocytes dominate hypercholesterolemia-associated monocytosis and give rise to macrophages in atheromata.

Macrophage accumulation participates decisively in the development and exacerbation of atherosclerosis. Circulating monocytes, the precursors of macrophages, display heterogeneity in mice and humans, but their relative contribution to atherogenesis remains unknown. We report here that the Ly-6C(hi) monocyte subset increased dramatically in hypercholesterolemic apoE-deficient mice consuming a high-fat diet, with the number of Ly-6C(hi) cells doubling in the blood every month. Ly-6C(hi) monocytes adhered to activated endothelium, infiltrated lesions, and became lesional macrophages. Hypercholesterolemia-associated monocytosis (HAM) developed from increased survival, continued cell proliferation, and impaired Ly-6C(hi) to Ly-6C(lo) conversion and subsided upon statin-induced cholesterol reduction. Conversely, the number of Ly-6C(lo) cells remained unaffected. Thus, we believe that Ly-6C(hi) monocytes represent a newly recognized component of the inflammatory response in experimental atherosclerosis.

Animals↗

PubMed2006

Monocyte accumulation in mouse atherogenesis is progressive and proportional to extent of disease.

Monocytes participate importantly in the pathogenesis of atherosclerosis, but their spatial and temporal recruitment from circulation remains uncertain. This study tests the hypothesis that monocyte accumulation in atheroma correlates with the extent of disease by using a sensitive and simple quantitative assay that allows tracking of highly enriched populations of blood monocytes. A two-step isolation method yielded viable and functionally intact highly enriched peripheral blood monocyte populations (>90%). Recipient mice received syngeneic monocytes labeled in two ways: by transgenically expressing EGFP or with a radioactive tracer [(111)In]oxine. After 5 days, more labeled cells accumulated in the aorta, principally the aortic root and ascending aorta, of 10-wk-old ApoE(-/-) compared with 10-wk-old C57BL/6 mice (223 +/- 3 vs. 87 +/- 22 cells per aorta). Considerably more monocytes accumulated in 20-wk-old ApoE(-/-) mice on either chow (314 +/- 41 cells) or high-cholesterol diet (395 +/- 53 cells). Fifty-week-old ApoE(-/-) mice accumulated even more monocytes in the aortic root, ascending aorta, and thoracic aorta after both chow (503 +/- 67 cells) or high-cholesterol diet (648 +/- 81 cells). Labeled monocyte content in the aorta consistently correlated with lesion surface area. These data indicate that monocytes accumulate continuously during atheroma formation, accumulation increases in proportion to lesion size, and recruitment is augmented with hypercholesterolemia. These results provide insights into mechanisms of atherogenesis and have implications for the duration of therapies directed at leukocyte recruitment.

Animals↗

PubMed2006

Regulatory T cells reversibly suppress cytotoxic T cell function independent of effector differentiation.

Mechanisms of dominant tolerance have evolved within the mammalian immune system to prevent inappropriate immune responses. CD4(+)CD25(+) regulatory T (T(reg)) cells have emerged as central constituents of this suppressive activity. By using multiphoton intravital microscopy in lymph nodes (LNs) of anesthetized mice, we have analyzed how cytotoxic T lymphocytes (CTLs) interact with antigen-presenting target cells in the presence or absence of activated T(reg) cells. Nonregulated CTLs killed their targets at a 6.6-fold faster rate than regulated CTLs. In spite of this compromised effector activity, regulated CTLs exhibited no defect in proliferation, induction of cytotoxic effector molecules and secretory granules, in situ motility, or ability to form antigen-dependent conjugates with target cells. Only granule exocytosis by CTLs was markedly impaired in the presence of T(reg) cells. This selective form of regulation did not require prolonged contact between CTLs and T(reg) cells but depended on CTL responsiveness to transforming growth factor-beta. CTLs quickly regained full killing capacity in LNs upon selective removal of T(reg) cells. Thus, T(reg) cells reversibly suppress CTL-mediated immunity by allowing acquisition of full effector potential but withholding the license to kill.

Animals↗

PubMed2006

Fluorescent nanoparticle uptake for brain tumor visualization.

Accurate delineation of tumor margins is vital to the successful surgical resection of brain tumors. We have previously developed a multimodal nanoparticle CLIO-Cy5.5, which is detectable by both magnetic resonance imaging and fluorescence, to assist in intraoperatively visualizing tumor boundaries. Here we examined the accuracy of tumor margin determination of orthotopic tumors implanted in hosts with differing immune responses to the tumor. Using a nonuser-based signal intensity method applied to fluorescent micrographs of 9L gliosarcoma green fluorescent protein (GFP) tumors, mean overestimations of 2 and 24 microm were obtained using Cy5.5 fluorescence, compared to the true tumor margin determined by GFP fluorescence, in nude mice and rats, respectively. To resolve which cells internalized the nanoparticle and to quantitate degree of uptake, tumors were disaggregated and cells were analyzed by flow cytometry and fluorescence microscopy. Nanoparticle uptake was seen in both CD11b+ cells (representing activated microglia and macrophages) and tumor cells in both animal models by both methods. CD11b+ cells were predominantly found at the tumor margin in both hosts, but were more pronounced at the margin in the rat model. Additional metastatic (CT26 colon) and primary (Gli36 glioma) brain tumor models likewise demonstrated that the nanoparticle was internalized both by tumor cells and by host cells. Together, these observations suggest that fluorescent nanoparticles provide an accurate method of tumor margin estimation based on a combination of tumor cell and host cell uptake for primary and metastatic tumors in animal model systems and offer potential for clinical translation.

Animals↗

PubMed2003

Ex vivo characterization of human CD8+ T subsets with distinct replicative history and partial effector functions.

After antigenic challenge, naive T lymphocytes enter a program of proliferation and differentiation during the course of which they acquire effector functions and may ultimately become memory cells. In humans, the pathways of effector and memory T-cell differentiation remain poorly defined. Here we describe the properties of 2 CD8+ T-lymphocyte subsets, RA+CCR7-27+28+ and RA+CCR7-27+28-, in human peripheral blood. These cells display phenotypic and functional features that are intermediate between naive and effector T cells. Like naive T lymphocytes, both subsets show relatively long telomeres. However, unlike the naive population, these T cells exhibit reduced levels of T-cell receptor excision circles (TRECs), indicating they have undergone additional rounds of in vivo cell division. Furthermore, we show that they also share effector-type properties. At equivalent in vivo replicative history, the 2 subsets express high levels of Fas/CD95 and CD11a, as well as increasing levels of effector mediators such as granzyme B, perforin, interferon gamma, and tumor necrosis factor alpha. Both display partial ex vivo cytolytic activity and can be found among cytomegalovirus-specific cytolytic T cells. Taken together, our data point to the presence of T cells with intermediate effector-like functions and suggest that these subsets consist of T lymphocytes that are evolving toward a more differentiated effector or effector-memory stage.

Adult↗

PubMed2002

Antigenicity and immunogenicity of Melan-A/MART-1 derived peptides as targets for tumor reactive CTL in human melanoma.

Some cancer patients mount spontaneous T- and B-cell responses against their tumor cells. Autologous tumor reactive CD8 cytolytic T lymphocyte (CTL) and CD4 T-cell clones as well as antibodies from these patients have been used for the identification of genes encoding the target antigens. This knowledge opened the way for new approaches to the immunotherapy of cancer. In this review, we describe the characterization of the structure-function properties of the melanocyte/melanoma tumor antigen Melan-A/MART-1, the assessment of the T-cell repertoire available against this antigen in healthy individuals, and the analysis of naturally acquired and/or vaccine-induced CTL responses to this antigen in patients with metastatic melanoma.

Amino Acid Sequence↗