The phenotype of CD4+ T cells capable of transendothelial migration was determined using an in vitro model system, in which cells migrate through a monolayer of endothelial cells (EC) on collagen gels. A specific subset of resting CD4+ memory T cells was found to migrate. T cells within this subset can be defined by the bright expression of CD11a, CD26, CD44, and CD49d. Additionally, the migratory CD4+ T cell population is largely CD58bright, CD31-, CD62L-, and is also enriched in cells that brightly express CD49c, CD49e, and CD49f. Only a minority of the cells are activated, as indicated by expression of CD69. The EC were found to play a central role in facilitating migration of this subset because selective enrichment of CD11abright, CD26bright, CD44bright, CD4+ T cells was not observed when cells migrated in the absence of EC. Activation of the T cells induced a modest degree of migration of an additional subset of CD45RA+, CD31+ naive T cells. In contrast, TNF-alpha activation of the EC increased the transendothelial migration of an additional subset of activated memory T cells that expressed CD69 and CD62L. Neither activation of the T cells, stimulation of the EC, nor the presence of macrophage inflammatory protein-1 alpha (MIP-1 alpha) or RANTES, however, altered the phenotype of the majority of the migratory CD4+ T cell population, which is characteristic of a particular stage of memory cell differentiation. These results suggest that CD4+ T cells acquire the capacity for transendothelial migration at a specific phase of maturation that is only minimally altered by the activation of either the T cell or the EC, or by the presence of specific chemokines in the subendothelial matrix.

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