On the front line of the immune system’s battle with pathogens, T cells raise the alarm and stimulate the body’s response to danger. They become activated when protein receptors on their surfaces detect an outsider, triggering a suite of cellular processes to eventually destroy the pathogen and promote its detection around the body. T-cell receptors are organised into minute nano-clusters, or protein islands, which, in cultured cells in the laboratory, are known to merge into larger micro-clusters when the cell becomes activated. For the first time, this behaviour has been observed in the cells’ natural environment, in a live animal, thanks to super-resolution microscopy; this image shows bright receptor micro-clusters in a mouse T cell. Researchers hope that a deeper understanding of T-cell activation will reveal ways of interfering with the responses of the immune system, in particular to tone them down in patients with autoimmune diseases.
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