α4β1-integrin activation is necessary for high-efficiency T-cell subset interactions with VCAM-1 under flow

Objective: The purpose of this study was to examine the relationship between alpha(4)beta(1)-integrin state of activation on CD4(+) T-cell subsets and their adhesive interaction to VCAM-1 under flow. Methods: 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 beta(1)-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 (k(a)), accumulation, and instantaneous rolling velocities were correlated to their beta(1)-integrin activation epitope expression. Results: A subset of memory T-cells constitutively express activation/ligand induced epitopes on beta(1)-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 beta(1)-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 alpha(4)-integrins or beta(1)-integrins, indicating that alpha(4)beta(1) is the predominant T-cell integrin involved. Conclusions: Memory T-cells express constitutively active alpha(4)beta(1)-integrins, as compared to naive T-cells, which mediate high rates of initial attachment and sustained high-affinity adhesive interactions with VCAM-1 under flow conditions in vitro. Similarly, in vitro differentiated Th2 cells but not Th1 cells, which also express elevated levels of activated alpha(4)beta(1)-integrins, are capable of sustaining high-affinity adhesive interactions with VCAM-1. The differences observed in beta(1)-integrin activation on T-cell subsets may underlie selective recruitment patterns of T-cell subsets in vivo.