alpha(4)beta(1)-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 betwee n 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 ef fector-helper T-cell subsets, Th1 and Th2 cells, were differentiated in vit ro from CD4(+) naive T-cells. The expression of activation/ligand induced e pitopes on beta(1)-integrins of each T-cell subset was assessed using mAb H UTS21 and mAb 15/7. T-cell subsets attachment and rolling on VCAM-1 was det ermined under defined flow conditions and the rates of attachment (k(a)), a ccumulation, and instantaneous rolling velocities were correlated to their beta(1)-integrin activation epitope expression. Results: A subset of memory T-cells constitutively express activation/ligan d 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. Consis tent with an activated phenotype, memory T-cells exhibit significantly high er 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 t o interact with VCAM-1 are comparable to memory T-cells. In contrast. Th1 c ells did not interact as efficiently with VCAM-1, which correlated with low er expression of activation/ligand induced epitopes on these cells. VCAM-1 interactions are inhibited completely by pretreatment of the T-cells with b locking mAb to alpha(4)-integrins or beta(1)-integrins, indicating that alp ha(4)beta(1) is the predominant T-cell integrin involved. Conclusions: Memory T-cells express constitutively active alpha(4)beta(1)-i ntegrins, as compared to naive T-cells, which mediate high rates of initial attachment and sustained high-affinity adhesive interactions with VCAM-1 u nder 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 intera ctions with VCAM-1. The differences observed in beta(1)-integrin activation on T-cell subsets may underlie selective recruitment patterns of T-cell su bsets in vivo.