T Cells (IMAGE) Dana-Farber Cancer Institute Caption A highly focused laser beam (at right) is used to apply mechanical force (shown as a double headed arrow) to a microsphere (white) coated with histocompatibility protein. The microsphere abuts the surface of a single T cell, shown in gray (top). Activation of the T cell is measured by a change in calcium levels within the cell, which are shown by green colorization (left, prior to force application; bottom, after force application). The direction of force must be tangential, rather than perpendicular, to the T cell surface in order to trigger a rise in calcium levels. Without an application of force, the binding of the histocompatibility protein produces no such rise. Credit Dana-Farber Cancer Institute Usage Restrictions Please credit Dana-Farber Cancer Institute License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.