Researchers have combined nanotechnology with biochemistry to create synthetic membranes that, for the first time, enable direct control of signalling activity in living T cells from the immune system, which could lead to better development of drugs for treating autoimmune diseases.
The new technique has already provided valuable insight into the impact that spatial arrangement has on the immunological synapse and its signalling strength. Such information should also help scientists better understand the chemical language by which cells communicate with one another.
"Combining inorganic nanotechnology with organic molecules and cells enables us to go inside a living cell and physically move around its signalling molecules with molecular precision," said Jay Groves, a chemist with Berkeley Lab's Physical Biosciences Division
"Our experimental beaker has now become the inside of living cells and we can watch chemical reactions take place there," he added.
Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley, developed synthetic membranes out of lipids which they assembled onto a substrate of solid silica so that the membranes were able to float freely a few nanometers above the substrate.
This enabled the researchers to preserve the membranes in their naturally fluid state, allowing lipids and T cell receptor proteins to diffuse and interact freely over macroscopic distances.
Groves and his colleagues were able to spatially mutate the geometric shapes of the immunological synapses by embedding the silica substrate with chrome lines that were only 100 nanometers (about one ten-millionth of an inch) wide.
These ultra-narrow chrome lines served as barriers that restricted the motion of membrane lipids and T cell receptor proteins.
Using electron-beam lithography, the researchers were able to configure the chrome lines into several distinct patterns, including simple parallel lines, grids, and a series of concentric hexagons.
The new technique for spatial mutation studies should be applicable to various intercellular signalling systems.
"Essentially, these experiments amount to using inorganic nanotechnology to physically grab a protein in a living cell and move it to another position in that cell - then watch how the cell responds," said Groves.
"Where the spatial position of molecules is rarely thought to play an important role in the outcome of a chemical reaction, with our experimental technique we are seeing that, in living cells, this is not the case. The spatial position encodes information which can be directly translated into altered chemical outcomes."
Scientists have been putting forward theories about how the strength and duration of signals that activate T cells are controlled by immunological synapses, without having been able to do direct experimentation of key factors.
The human immune system starts when "antigens," identify another cell as "non-self," and signals the immune system to kill the invader.
Leading this attack will be the T cells, lymphocytes from the thymus. It is well established that the key to T cell activation is the molecular signal coming off antigen presenting cell surfaces.
This signal must be enhanced and sustained long enough for the T cells to commit to mounting an immune response, and then must be cut off in time to avoid antigen-induced cell suicide or "apoptosis" of the T cells.
It has been established that the control centre for T cell signalling is at the junction or point of contact between T cells and antigens, dubbed the "immunological synapse," a central cluster of T cell receptors surrounded by a ring of adhesion molecules
The centre has been dubbed the "central supramolecular activation cluster," or c-SMAC, because it was believed to be the source of T cell activation.
"The original idea behind the c-SMAC was that the larger the T cell receptor cluster, the stronger the T cell activation signal," said Groves.
"This simple vision of strength in numbers had begun to show cracks, and now we have demonstrated that just the opposite is true, the coalescence of the c-SMAC cluster extinguishes the T cell activation signal. The duration of the activation signal is related to the spatial organisation of the T cell receptors rather than cluster size."
By changing the shape of the immunological synapse, the team demonstrated the synapse signal started out in an amplified mode, and the transport of the T cell receptors towards the centre weakened, eventually extinguishing the signal, irrespective of the degree of clustering.
This may help explain why diseases of the autoimmune system are so difficult to treat. T cell receptor proteins do not respond like a conventional target. However, if the bull's eye is hit a signal is triggered. The spatial position of the receptor determines the type of signal it triggers.
Already, Groves and his colleagues have begun applying it to study neuronal synapse formation, and cell signalling mechanisms in the development of cancer. They are also using it to look at the dynamic range of signalling over which T cell receptors can respond.
The paper, "Altered TCR Signalling from Geometrically Repatterned Immunological Synapses," is published in the November 18, 2005 issue of the journal Science.