UC Irvine

T-cell contact with antigen-presenting B cells initiates an activation cascade which includes an increase in T-cell intracellular calcium and leads to T-cell proliferation and differentiation. We studied cell-cell contact requirements for T-cell activation using an optical trap to control the orientation of T-cell/B-cell pairs and fluorescence microscopy to measure subsequent T-cell [Ca2+]i response. B cells or beads coated with antibodies to the T-cell receptor (TCR) are trapped with a titanium-sapphire laser and placed at different locations along the T-cell, which has a polarized appearance defined by die shape and direction of crawling. T-cell [Ca2+]i is detected as an emission shift from the combination of fura-red and Oregon-green, two cytoplasmic [Ca2+] indicators. T cells which are presented antigen at the leading edge have a higher probability of responding and a shorter latency of response than those contacting B-cells or beads with their trailing end.