Requirement for G proteins in T lymphoblast interaction with the spinal cord white matter microvasculature. (a) Presence of high-affinity α4-integrin on encephalitogenic T cell blasts but not on resting T cells is demonstrated by binding of VCAM-1–Ig (thick line) as determined by FACS-analysis. Binding of HT7-Ig was used as control (thin line). (b and c) Capture events (b) and normalized velocity (c) of pertussis toxin–pretreated T cell blasts. Objective assessment of PTX-pretreated T lymphoblast/endothelial interaction was obtained by comparing the velocity distribution of T cells observed in vessels of comparable size. For the control group 160 cells in seven postcapillary venules of two mice and for the pertussis toxin group 190 cells in 15 postcapillary venules of three mice were analyzed. V_crit, the velocity of an idealized noninteracting T cell blast, was calculated as described in Methods. Ten percent of circulating T cells were transiently captured at the vascular wall (b). PTX did not influence the number of captured T cells (b). Lack of T lymphoblast rolling is demonstrated by the lack of T cells traveling at velocities below V_crit (c). (d) Quantitative analysis of permanent T lymphoblast adherence within spinal cord white matter microvasculature. T lymphoblasts permanently adhering within spinal cord white matter microvasculature were counted 10 minutes, 1 hour, and 2 hours after infusion of 3 × 10⁶ PLP-specific T cell blasts by intravital fluorescence videomicroscopy using epi-illumination techniques as described in Methods. Number of mice included in this analysis per group: PBS-control, n = 2; MTX:, n = 2; PTX, n = 3. Asterisks indicate significant differences.