Coordinate expression of β1 and β2 integrin “activation” epitopes during T cell responses in secondary lymphoid tissue

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Abstract
The monoclonal antibodies (mAb) 15/7 and 24 recognize unique activation‐dependent, conformational epitopes on β1 and β 2‐integrins, respectively. The expression of both of these epitopes closely correlates with the ligand binding ability of their respective integrins, and thus serves as indicators of functional integrin “activation”. Here, we have used six‐parameter flow cytometry to examine the expression of these epitopes and conventional β1‐ and β2‐integrin epitopes during human T cell activation in secondary lymphoid tissues in vivo, focusing particularly on the virgin to memory/effector cell transition. Fresh tonsil lymphocytes were stained with mAb against conventional or activation‐dependent integrin epitopes, followed by staining with mAb against CD3, CD45RA, and CD45RO, thus allowing the determination of integrin epitope expression on virgin (CD3+) T cells (CD45RA+/RO−to±), memory/effector (CD45RA−/RO++) T cells, and T cells undergoing the virgin to memory/effector transition: transition region‐1 (T1; CD45RA+to++/RO+); ‐2 (T2; CD45RA++/RO++); and ‐3 (T3; CD45RA+/RO++). Conventional β1‐ and β2‐integrin epitopes progressively increase during the virgin to T3 stages of the transition in tonsil, in keeping with the generally higher levels of these adhesion molecules on memory/effector vs. virgin T cells. Expression of both the β1 (15/7)‐and β2 (24)‐integrin activation epitopes first appears on transitional T cells, and is maintained on a relatively constant number of cells (averaging 25‐30%) throughout the T1‐T3 stages. These epitopes are also noted on a subset of activated memory/effector T cells. Importantly, on both transitional and activated memory/effector T cell subsets, the expression patterns of the 15/7 and 24 epitopes vs. a variety of T cell activation antigens are identical, and the expression of these epitopes relative to each other is linearly correlated, findings strongly supporting the coordinate activation of β1 and β2 integrins duringT cell activation in vivo. These results provide the first evidence of integrin activation during an in vivo immunologic response, and demonstrate the usefulness of mAb recognizing conformational epitopes and multiparameter flow cytometry in delineating the dynamic interplay of adhesion molecules during complex physiologic processes.