periods from 2 to 36 hours are required for migration through the construct (e.g [7-9]). In such
systems, T-cells spontaneously migrated through unstimulated endothelium/filters over time, [7,
10, 11], although the proportion migrating only reached about 10% of those added. Perhaps
surprisingly, treatment of the EC with a range of cytokines (IL-1, TNF, IFN or TNF+IFN) caused
modest [12, 13] or negligible [8, 10, 14] increases in T cell transmigration compared to
unstimulated EC, again over prolonged periods. Addition of inflammatory chemokines, such as
CCL2 (MCP-1), CCL3 (MIP-1α) or CCL5 (RANTES), below the filter slightly increased
migration of memory T cells, although CXCL12 (a homeostatic chemokine) caused marked
increase in the migration for naɪve and memory T-cells [12]. Transendothelial migration studies
have also been carried out for EC grown directly on collagen gels, where quite a small proportion
of added T cells (~10%) migrated into the gel over 2-4h, and cytokine stimulation of the EC
again had little effect [15, 16].
Considering the T-cell phenotype, memory CD4+ T-cells migrated more efficiently than
naive cells through resting or cytokine-treated EC (e.g [14, 16]), and in the presence of a
chemotactic gradient [12]. Transmigration of T-cells tends to be increased by stimulation prior to
assay, for instance, incubation with phorbol dibutyrate (PDB) or IL-2, culture for 2 to 24 hours
(which up-regulates expression of αLβ2-integrin), or differentiation over weeks [7-10].
Nevertheless, studies using freshly isolated lymphocytes without manipulation reported migration
through resting or IL-1β stimulated EC at 24h [11, 14] comparable to that observed in others
studies when T cells were cultured overnight (e.g. [7]). It should be noted that in the studies
described above, where transendothelial migration occurred in minutes under flow, the T-cells
had first been subjected to prolonged incubation in presence [5] or absence of IL-2 [3, 6].