Biomedical subjects

Lawrence J Stern

Publications and source records attributed to Lawrence J Stern.

23 records · Page 2Linked to original sources

PubMed2002

Soluble peptide-MHC monomers cause activation of CD8+ T cells through transfer of the peptide to T cell MHC molecules.

T cell receptor (TCR)-mediated activation of CD4(+) T cells is known to require multivalent engagement of the TCR by, for example, oligomeric peptide-MHC complexes. In contrast, for CD8(+) T cells, there is evidence for TCR-mediated activation by univalent engagement of the TCR. We have here compared oligomeric and monomeric L(d) and K(b) peptide-MHC complexes and free peptide as stimulators of CD8(+) T cells expressing the 2C TCR. We found that the monomers are indeed effective in activating naive and effector CD8(+) T cells, but through an unexpected mechanism that involves transfer of peptide from soluble monomers to T cell endogenous MHC (K(b)) molecules. The result is that T cells, acting as antigen-presenting cells, are able to activate other naive T cells.

Amino Acid Sequence↗

PubMed2002

Labeling antigen-specific CD4(+) T cells with class II MHC oligomers.

Class I MHC-peptide oligomers (MHC tetramers) have become popular reagents for the detection and characterization of antigen-specific CD8(+) T cells. Class II MHC proteins can be produced by expression in Escherichia coli followed by in vitro folding, or by native expression in insect cells; biotin can be introduced by site-specific chemical modification of cysteine, or by enzymatic modification of a peptide tag; and a variety of fluorescent streptavidin preparations can be used for oligomerization. Here we review methodologies for production of fluorescent oligomers of soluble class II MHC proteins and discuss their use in analysis of antigen-specific CD4(+) T cells. We explore the experimental conditions necessary for efficient staining of CD4(+) T cells using oligomers of class II MHC proteins, and we establish a standard protocol. Finally, we consider complications and challenges associated with these reagents, discuss the interpretation of staining results, and suggest future directions for investigation, in particular the use of MHC oligomers for the study of T cell avidity modulation.

Amino Acid Sequence↗

PubMed2002

Granulocyte-macrophage colony-stimulating factor induces an expression program in neonatal microglia that primes them for antigen presentation.

Neonatal microglial cells respond to GM-CSF and M-CSF by acquiring different morphologies and phenotypes. To investigate the extent and consequences of this process, a global gene expression analysis was performed, with significant changes in transcript levels confirmed by biochemical analyses. Primary murine microglial cells underwent substantial expression reprogramming after treatment with GM-CSF or M-CSF with many differentially expressed transcripts important in innate and adaptive immunity. In particular, many gene products involved in Ag presentation were induced by GM-CSF, but not M-CSF, thus potentially priming relatively quiescent microglia cells for Ag presentation. This function of GM-CSF is distinct from its primary function in cell proliferation and survival.

Animals↗

PubMed2002

Cutting edge: TCR engagement and triggering in the absence of large-scale molecular segregation at the T cell-APC contact site.

We investigated the functional role of large-scale molecular segregation at the T cell-APC contact site during T lymphocyte Ag recognition. Inhibition of CD2-CD58 interaction markedly affected segregation of CD2 and CD2AP from CD45. Under these conditions, Ag-induced calcium mobilization, PKC theta; clustering at the immunological synapse, and IFN-gamma production also were inhibited. However, early TCR signaling and T cell polarization toward APCs were unaffected. Our results indicate that the "raison d'être" of a large-scale segregation of surface molecules and intracellular enzymes and adapters, in Ag-stimulated T cells, is to reinforce the assembly of the signal transduction cascade rather than favor TCR engagement and triggering.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Dihydrolipoic acid as an effective cofactor for peptide methionine sulfoxide reductase in enzymatic repair of oxidative damage to both lipid-free and lipid-bound apolipoprotein a-I.

The aim of this study was to examine the possible use of dihydrolipoic acid (DHLA), the reduced form of lipoic acid, in the reduction of oxidized apolipoprotein A-I mediated by peptide methionine sulfoxide reductase (PMSR), and to test the accessibility of methionine sulfoxides in the lipid-bound oxidized apolipoprotein A-I to this reaction. We show that DHLA acts as an effective cofactor for PMSR, mediating restoration of the native secondary structure, tertiary structure, stability, and lipid-binding properties of the native unoxidized protein. Reconstituted high-density lipoproteins were used to demonstrate effective enzymatic reduction of the lipid-bound oxidized protein in the presence of DHLA. These findings suggest that the enzymatic repair of oxidative damage to intact lipoproteins could provide a model of a possible repair mechanism active in vivo during oxidative stress and that the restoration of high-density lipoprotein function could be one of the therapeutic benefits of lipoic acid.

Apolipoprotein A-I↗