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Biomedical subjects

G Marland

Publications and source records attributed to G Marland.

14 recordsLinked to original sources
PubMed2002

Net carbon flux from agricultural ecosystems: methodology for full carbon cycle analyses.

Agricultural ecosystems have the potential to sequester carbon in soils by altering agricultural management practices (i.e. tillage practice, cover crops, and crop rotation) and using agricultural inputs (i.e. fertilizers and irrigation) more efficiently. Changes in agricultural practices can also cause changes in CO2 emissions associated with these practices. In order to account for changes in net CO2 emissions, and thereby estimate the overall impact of carbon sequestration initiatives on the atmospheric CO2 pool, we use a methodology for full carbon cycle analysis of agricultural ecosystems. The analysis accounts for changes in carbon sequestration and emission rates with time, and results in values representing a change in net carbon flux. Comparison among values of net carbon flux for two or more systems, using the initial system as a baseline value, results in a value for relative net carbon flux. Some results from using the full carbon cycle methodology, along with US national average values for agricultural inputs, indicate that the net carbon flux averaged over all crops following conversion from conventional tillage to no-till is -189 kg C ha(-1) year(-1) (a negative value indicates net transfer of carbon from the atmosphere). The relative net carbon flux, using conventional tillage as the baseline, is -371 kg C ha(-1) year(-1), which represents the total atmospheric CO2 reduction caused by changing tillage practices. The methodology used here illustrates the importance of (1) delineating system boundaries, (2) including CO2 emissions associated with sequestration initiatives in the accounting process, and (3) comparing the new management practices associated with sequestration initiatives with the original management practices to obtain the true impact of sequestration projects on the atmospheric CO2 pool.

Agriculture↗
PubMed1997

A dendritic-cell-derived C-C chemokine that preferentially attracts naive T cells.

Dendritic cells form a system of highly efficient antigen-presenting cells. After capturing antigen in the periphery, they migrate to lymphoid organs where they present the antigen to T cells. Their seemingly unique ability to interact with and sensitize naive T cells gives dendritic cells a central role in the initiation of immune responses and allows them to be used in therapeutic strategies against cancer, viral infection and other diseases. How they interact preferentially with naive rather than activated T lymphocytes is still poorly understood. Chemokines direct the transport of white blood cells in immune surveillance. Here we report the identification and characterization of a C-C chemokine (DC-CK1) that is specifically expressed by human dendritic cells at high levels. Tissue distribution analysis demonstrates that dendritic cells present in germinal centres and T-cell areas of secondary lymphoid organs express this chemokine. We show that DC-CK1, in contrast to RANTES, MIP-1alpha and interleukin-8, preferentially attracts naive T cells (CD45RA+). The specific expression of DC-CK1 by dendritic cells at the site of initiation of an immune response, combined with its chemotactic activity for naive T cells, suggests that DC-CK1 has an important rule in the induction of immune responses.

Amino Acid Sequence↗
PubMed1997

Analysis of dendritic cells at the genetic level.

To increase our understanding of dendritic cell (DC) function we have used two approaches to search at the genetic level for molecules which are specifically expressed by these cells. First, we have performed random sequencing of cDNA libraries prepared from DC. Second, we have employed differential display PCR (DD-PCR). DD-PCR is a powerful technique for the identification at the RNA level of molecules which are expressed in a cell type-specific manner. In our study, we have compared RNA from DC with RNA from a panel of leukocyte cell lines. Here we present a summary of our findings using these two approaches, and show that both methods are complementary and can be used to identify molecules that are specific to DC.

Antigen Presentation↗
PubMed1996

Dendritic cells in immune response induction.

The study of dendritic cells (DCs) has seen a rapid expansion in recent years, and their importance within the immune system is now widely recognized. Along with B lymphocytes and mononuclear phagocytes, DCs make up what are known as the professional antigen-presenting cells (APCs). These are cells which are capable of highly efficiently presenting antigens to the immune system in the context of both major histocompatibility complex class I and class II molecules. What makes DCs stand out from other professional APCs, however, is their seemingly unique ability to present antigen to T lymphocytes which have had no previous contact with antigen. This gives DCs central role in the initiation of immune responses, and creates possibilities for their exploitation in the development of therapeutic strategies against tumors and other diseases. What are the characteristics of DCs which enable them to carry out their specialized function? This is a question which is currently gaining much interest. While higher expression levels of the antigen-presentation machinery may account for this, there may also be as yet unidentified mechanisms at work. In this review, we will discuss the evidence for DC-mediated priming of both CD4+ and CD8+ naive T cells, both in vitro and in vivo, current ideas on how DCs achieve their potent function and the implications for the design and execution of immunotherapeutic strategies.

Animals↗
PubMed1995

Generation of antimelanoma cytotoxic T lymphocytes from healthy donors after presentation of melanoma-associated antigen-derived epitopes by dendritic cells in vitro.

MHC class I-restricted CTLs specific for antigens expressed by malignant cells are an important component of immune responses against human cancer. Recently, in melanoma a number of melanocyte differentiation antigens have been identified as potential tumor rejection antigens. In the present study, we show that by applying peptide-loaded dendritic cells, induced by granulocyte-macrophage colony-stimulating factor and interleukin 4 from peripheral blood monocytes of healthy donors, we were able to elicit melanoma-associated antigen-specific CTL in vitro. We demonstrate the induction of CTLs directed against HLA-A2.1 presented epitopes derived from tyrosinase, gp100, and Melan A/MART-1. Apart from lysis of peptide-loaded target cells, these CTLs displayed reactivity with HLA-A2.1+ melanoma tumor cell lines and cultured normal melanocytes endogenously expressing the target antigen. These data indicate that these CTLs recognize naturally processed and presented epitopes and that precursor CTLs against melanocyte differentiation antigens are present in healthy individuals. The ability to generate tumor-specific CTLs in vitro, using granulocyte-macrophage colony-stimulating factor/interleukin 4-induced dendritic cells, illustrates the potential use of this type of antigen-presenting cells for vaccination protocols in human cancer.

Amino Acid Sequence↗
PubMed1994

Mutation of aspartate 82 of the human C5a receptor abolishes the secretory response to human C5a in transfected rat basophilic leukemia cells.

C5a is a potent chemoattractant for monocytes, neutrophils and other leukocytes. The receptor for human C5a is a member of the rhodopsin superfamily of G protein-coupled receptors and contains an aspartate residue (Asp82) within the putative second transmembrane domain conserved in all other G protein-linked receptors. We investigated the role of this residue and also the carboxy-terminal 23 residues of the C5a receptor in ligand binding and signal transduction by expressing wild-type and mutant receptors in the rat basophilic leukemia cell line RBL-2H3. Wild-type and truncated receptors coupled efficiently to effector systems, resulting in the C5a-dependent discharge of granule contents. In contrast RBL cells transfected with receptors in which Asp82 had been mutated to asparagine did not respond to human C5a by secretion despite binding human C5a with high affinity. We conclude therefore that Asp82 is not involved in the interaction with ligand but is essential for the proper transduction of the ligand binding signal.

Animals↗
PubMedDate not supplied

The reflective diary: an aid to practice-based learning.

This article explores the use of reflective learning diaries in conjunction with a modified form of the Benner assessment tool (Benner 1984). The authors describe a practicum, based on the findings of a small action research study for the development and use of reflective diaries during clinical placement. The results suggest that students, preceptors, reflective diaries and assessment tools can be combined to create a positive learning environment.

Competency-Based Education↗