Analysis of detergent-free lipid rafts isolated from CD4 + T cell line: interaction with antigen presenting cells promot
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RESEARCH
Open Access
Analysis of detergent-free lipid rafts isolated from CD4+ T cell line: interaction with antigen presenting cells promotes coalescing of lipid rafts Colleen Kennedy1,2, Matthew D Nelson1,3 and Anil K Bamezai1*
Abstract Background: Lipid rafts present on the plasma membrane play an important role in spatiotemporal regulation of cell signaling. Physical and chemical characterization of lipid raft size and assessment of their composition before, and after cell stimulation will aid in developing a clear understanding of their regulatory role in cell signaling. We have used visual and biochemical methods and approaches for examining individual and lipid raft sub-populations isolated from a mouse CD4+ T cell line in the absence of detergents. Results: Detergent-free rafts were analyzed before and after their interaction with antigen presenting cells. We provide evidence that the average diameter of lipid rafts isolated from un-stimulated T cells, in the absence of detergents, is less than 100 nm. Lipid rafts on CD4+ T cell membranes coalesce to form larger structures, after interacting with antigen presenting cells even in the absence of a foreign antigen. Conclusions: Findings presented here indicate that lipid raft coalescence occurs during cellular interactions prior to sensing a foreign antigen. Keywords: raft coalescence, CD4+ T cells, antigen presenting cells, electron microscopy, raft-ELISA
Background Signals emanating from the plasma membrane have spatial and temporal components [1-5]. Spatial distribution and accessibility of signaling proteins on the plasma membrane can potentially have profound effects on the outcome of signaling. While knowledge of temporal signaling events has rapidly advanced, the spatial distribution of signaling proteins remains unclear. More so, how the spatial distribution of signaling molecules relates to temporal signaling is unknown. However, recently, re-organization on the plasma membrane of quiescent cells was recognized after triggering signaling from the membrane [6-11]. Lipid raft membrane domains are rich in cholesterol and sphingolipids and known to compartmentalize signaling proteins [12-17]. Heterogeneity of lipid rafts, with respect to protein composition, on the plasma * Correspondence: [email protected] 1 Department of Biology, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA Full list of author information is available at the end of the article
membrane may provide an additional level of spatial segregation [18-26]. Ligand and receptor induced molecular interactions on the plasma membrane trigger a signaling cascade that culminates into specific gene expression. Compositional heterogeneity of lipid rafts on the surface of quiescent cells and their subsequent coalescence, when the receptors engage their ligands, might promote interactions between appropriate signaling proteins [14,27]. However, this is only one of several proposed models to explain signal transduction from the plasma membrane to the interior of the ce
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