['The purpose of this study was to examine the relationship between alpha4beta1-integrin state of activation on CD4+ T-cell subsets and their adhesive interaction to VCAM-1 under flow.', 'Human CD4+ memory and naive T-cells were freshly isolated and effector-helper T-cell subsets. Th1 and Th2 cells, were differentiated in vitro from CD4+ naive T-cells. The expression of activation/ligand induced epitopes on beta1-integrins of each T-cell subset was assessed using mAb HUTS21 and mAb 15/7. T-cell subsets attachment and rolling on VCAM-1 was determined under defined flow conditions and the rates of attachment (ka), accumulation, and instantaneous rolling velocities were correlated to their beta1-integrin activation epitope expression.', 'A subset of memory T-cells constitutively express activation/ligand induced epitopes on beta1-integrins recognized by mAb HUTS21 and 15/7, whereas expression levels on naive T-cells is low or not detectable. Consistent with an activated phenotype, memory T-cells exhibit significantly higher rates of attachment and accumulation on VCAM-1 under flow as compared to naive T-cells. Interestingly, the expression of activation/ligand induced epitopes on beta1-integrins on Th2 cells and the ability of these cells to interact with VCAM-1 are comparable to memory T-cells. In contrast, Th1 cells did not interact as efficiently with VCAM-1, which correlated with lower expression of activation/ligand induced epitopes on these cells. VCAM-1 interactions are inhibited completely by pretreatment of the T-cells with blocking mAb to alpha4-integrins or beta1-integrins, indicating that alpha4beta1 is the predominant T-cell integrin involved.'] Is alpha4beta1-integrin activation necessary for high-efficiency T-cell subset interactions with VCAM-1 under flow?