Figure 3.

The stop signal is reversible by adhesion strengthening phorbol esters, but does not require increased cytoplasmic Ca²⁺. (a) Effect of PMA. 3A9 T cells were treated with 50 ng/ml PMA as indicated: pre indicates 15-min pretreatment before exposure to bilayers, post indicates addition of PMA after cells were exposed to bilayers for 30 min. 3A9 T cells treated with PMA for 1 h had 75% as much TcR on the surface as control cells. Cells were maintained in recombinant IL-2 so the basal migration was slower. Data from three experiments. (b) Effect of cytoplasmic Ca²⁺ increase. 3A9 T cell migration was examined in normal Ca²⁺ media or in low Ca²⁺ media with 500 nM thapsigargin treatment as indicated. These cells had been maintained in the EL-4 supernatant. Data from two experiments. All bilayers have 800 molecules per μm² of ICAM-1 with or without 20 molecules per μm² of I-A^k–HEL48–62.