This number was divided by the known total number of PBL added, to obtain the percentage of the selleck products PBL that had adhered. At the endothelial layer, the PBL count was divided into those which were phase bright (above EC; fraction X) and those which were phase dark (migrated just below EC; fraction

Y). From these counts and the sum of PBL further into the gel (fraction Z), the percentages of adherent PBL that had undergone transendothelial migration ((Y + Z) / (X + Y + Z)) × 100% and the percentage of migrated cells that had penetrated into the collagen gel (Z / (Y + Z)) × 100% were calculated. The vertical position of those cells within the gels was also recorded. This was done by counting PBL in 18 μm ‘slices’ made up from 5 consecutive images (starting after the image of the endothelial monolayer referred to above), and assigning them a depth equal to the midpoint of that slice. The average depth of penetration was calculated by multiplying the midpoint depth by the number of cells found within that slice (averaged for the 5 fields), summing these values, and dividing the sum by the total number

of cells in the stack. The total gel thickness was also measured (from endothelial layer to base of dish), and the proportion of PBL within the upper and lower halves of the gel was also calculated. In addition, fibroblasts in the gel were counted and depth assigned in a similar manner; these large extended cells could appear in multiple images, and their nucleus was used to assign location. Several variants on this procedure were used for comparison. PBL were added to HUVEC on ‘empty’ gels, or added to Baf-A1 in vitro gels which contained fibroblasts but did not have an endothelial layer, or added to empty gels. Incubation and analysis of numbers and position of cells were carried out essentially as before. Percentage of PBL entering the gels in the latter cases (without a HUVEC layer) were calculated from the total number Urease added to the top of the gel or relative

to the blank gel control. In separate assays, with HUVEC cultured on filters above gels (Fig. 1C), PBL were added to the filter and incubated as above for 24 h. At that time, non-adherent cells were washed from the filter and counted, the filter was removed, and the gel was then analysed as above for the number and position of PBL on or in it. In some cases, the culture was then returned to the incubator, and position of PBL re-evaluated after a further 20 h. At the end of the imaging of gels, constructs in which endothelial cells were cultured on the surface of the gel were treated with dispase II (1 mg/ml; Sigma) for 15 min to dissociate the endothelial monolayer and lymphocytes associated with it. After microscopic check of dissociation, the cells were collected using two washes with M199BSA. For gels without endothelial monolayers, non-adherent cells were collected from the top by two similar washes.