IL-8 responsiveness of nonactivated versus activated CD8⁺ T cells. (A) F-actin was visualized in unstimulated and PHA-stimulated CD8⁺ T cells exposed to increasing concentrations of IL-8. In absence of IL-8, only cortical F-actin was visualized. An increasingly dense meshwork of F-actin throughout the cytoplasm was observed in most activated CD8⁺ T cells exposed to 10, 100, and 500 ng/mL IL-8 (bottom row). By contrast, in nonactivated CD8⁺ T cells a similar though less dense meshwork was formed only at 500 ng/mL IL-8 and only in some of the cells (top row) (representative of n = 3). (B) Chemotactic activity toward IL-8 was assessed in PHA-activated versus unstimulated CD8⁺ T cells. PHA activation (and hence up-regulation of CXCR1) sensitized CD8⁺ T cells for chemotactic activity toward IL-8 (representative of n = 4). *P < .05 between the chemotactic index of activated versus nonactivated CD8⁺ T cells; ^ P < .05 between background migration versus chemotaxis of nonactivated CD8⁺ T cells. Note that in activated CD8⁺ T cells significant chemotactic activity was observed already toward 1 ng/mL of IL-8. (C) In contrast to IL-8, only minimal chemotactic activity of nonactivated (NA) as well as activated (A) CD8⁺ T cells was observed in a gradient toward 1 ng/mL of IP-10 or MIP-1β (representative of n = 3). Error bars indicate mean ± SD.