Lineage choice is of great interest in developmental biology. In the immune system, the alphabeta and gammadelta lineages of T lymphocytes diverge during the course of the beta-, gamma- and delta-chain rearrangement of T-cell receptor (TCR) genes that takes place within the same precursor cell and which results in the formation of the gammadeltaTCR or pre-TCR proteins. The pre-TCR consists of the TCRbeta chain covalently linked to the pre-TCRalpha protein, which is present in immature but not in mature T cells which instead express the TCRalpha chain. Animals deficient in pre-TCRalpha have few alphabeta lineage cells but an increased number of gammadelta T cells. These gammadelta T cells exhibit more extensive TCRbeta rearrangement than gammadelta T cells from wild-type mice. These observations are consistent with the idea that different signals emanating from the gammadeltaTCR and pre-TCR instruct lineage commitment. Here we show, by using confocal microscopy and biochemistry to analyse the initiation of signalling, that the pre-TCR but not the gammadeltaTCR colocalizes with the p56lck Src kinase into glycolipid-enriched membrane domains (rafts) apparently without any need for ligation. This results in the phosphorylation of CD3epsilon and Zap-70 signal transducing molecules. The results indicate clear differences between pre-TCR and gammadeltaTCR signalling.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.
"Alternatively, TCR (and other immunoreceptors) may be pre-associated with membrane rafts  and its ligation just reorganizes somehow this assembly to allow for optimal exposure of the CD3 and f chains to the SFKs. The importance of membrane rafts immunoreceptor signaling is supported by findings that palmitoylation-deficient mutants of several of the raft resident proteins such as SFKs, CD8b, pre-TCR or LAT      are excluded from the rafts which results in functional defects. A fraction of a negative regulator of Src-family kinases activity, the protein tyrosine kinase (PTK) Csk, is also found in membrane rafts, due to its association with the phosphorylated transmembrane adaptor protein PAG (''phosphoprotein associated with GEMs'') also called Cbp (''Csk binding protein'')  , a palmitoylated membrane raft resident molecule. "
[Show abstract][Hide abstract] ABSTRACT: Membrane microdomains denoted commonly as lipid rafts (or membrane rafts) have been implicated in T-cell receptor (TCR), and more generally immunoreceptor, signaling for over 25 years. However, this area of research has been complicated by doubts about the real nature (and even existence) of these membrane entities, especially because of methodological problems connected with possible detergent artefacts. Recent progress in biophysical approaches and functional studies of raft resident proteins apparently clarified many controversial aspects in this area. At present, the prevailing view is that these membrane microdomains are indeed involved in many aspects of cell biology, including immunoreceptor signaling. Moreover, several other types of raft-like microdomains (perhaps better termed nanodomains) have been described, which apparently also play important biological roles.
"Lipid rafts constitute about 30–40% of mammalian cell membranes –. Ligand-mediated clustering of neighboring receptor subunits into rafts leads to the assembly of fully functional receptors able to signal for T cell development, maturation, activation, and differentiation –. These processes occur upon formation of T cell-APC immunological synapse and TCR- peptide-MHC complex interactions , . "
[Show abstract][Hide abstract] ABSTRACT: Cell signaling for T-cell growth, differentiation, and apoptosis is initiated in the cholesterol-rich microdomains of the plasma membrane known as lipid rafts. Herein, we investigated whether enrichment of membrane cholesterol in lipid rafts affects antigen-specific CD4 T-helper cell functions. Enrichment of membrane cholesterol by 40–50% following squalene administration in mice was paralleled by an increased number of resting CD4 T helper cells in periphery. We also observed sensitization of the Th1 differentiation machinery through co-localization of IL-2Rα, IL-4Rα, and IL-12Rβ2 subunits with GM1 positive lipid rafts, and increased STAT-4 and STAT-5 phosphorylation following membrane cholesterol enrichment. Antigen stimulation or CD3/CD28 polyclonal stimulation of membrane cholesterol-enriched, resting CD4 T-cells followed a path of Th1 differentiation, which was more vigorous in the presence of increased IL-12 secretion by APCs enriched in membrane cholesterol. Enrichment of membrane cholesterol in antigen-specific, autoimmune Th1 cells fostered their organ-specific reactivity, as confirmed in an autoimmune mouse model for diabetes. However, membrane cholesterol enrichment in CD4+
Foxp3+ T-reg cells did not alter their suppressogenic function. These findings revealed a differential regulatory effect of membrane cholesterol on the function of CD4 T-cell subsets. This first suggests that membrane cholesterol could be a new therapeutic target to modulate the immune functions, and second that increased membrane cholesterol in various physiopathological conditions may bias the immune system toward an inflammatory Th1 type response.
PLoS ONE 06/2012; 7(6):e38733. DOI:10.1371/journal.pone.0038733 · 3.23 Impact Factor
"Whether ligand-independent signaling by the pre-TCR is a property unique to this receptor or a general property of DN thymocytes is a matter of debate. The ability of the pre-TCR to localize in lipid rafts in the absence of ligand engagement has argued for the uniqueness of this receptor (4). The palmitoylation of a juxtamembrane cysteine residue uniquely present on pre-Tα chains was initially thought to be necessary for pre-TCR raft associations, but this residue has recently been shown to be dispensable for pre-TCR signaling (5–8). "
[Show abstract][Hide abstract] ABSTRACT: During T cell development in the thymus, pre-T cell receptor (TCR) complexes signal CD4(-) CD8(-) (double negative [DN]) thymocytes to differentiate into CD4(+) CD8(+) (double positive [DP]) thymocytes, and they generate such signals without apparent ligand engagements. Although ligand-independent signaling is unusual and might be unique to the pre-TCR, it is possible that other TCR complexes such as alphabeta TCR or alphagamma TCR might also be able to signal the DN to DP transition in the absence of ligand engagement if they were expressed on DN thymocytes. Although alphagamma TCR complexes efficiently signal DN thymocyte differentiation, it is not yet certain if alphabeta TCR complexes are also capable of signaling DN thymocyte differentiation, nor is it certain if such signaling is dependent upon ligand engagement. This study has addressed these questions by expressing defined alphabeta TCR transgenes in recombination activating gene 2(-/-) pre-Talpha(-/-) double deficient mice. In such double deficient mice, the only antigen receptors that can be expressed are those encoded by the alphabeta TCR transgenes. In this way, this study definitively demonstrates that alphabeta TCR can in fact signal the DN to DP transition. In addition, this study demonstrates that transgenic alphabeta TCRs signal the DN to DP transition even in the absence of their specific MHC-peptide ligands.
Journal of Experimental Medicine 07/2004; 199(12):1719-24. DOI:10.1084/jem.20032204 · 12.52 Impact Factor