COORDINATE EXPRESSION OF BETA-1 AND BETA-2 INTEGRIN ACTIVATION EPITOPES DURING T-CELL RESPONSES IN SECONDARY LYMPHOID-TISSUE

The monoclonal antibodies (mAb) 15/7 and 24 recognize unique activatio n-dependent, conformational epitopes on beta 1 and beta 2-integrins, r espectively. The expression of both of these epitopes closely correlat es 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 o f these epitopes and conventional beta 1- and beta 2-integrin epitopes during human T cell activation in secondary lymphoid tissues in vivo, focusing particularly on the virgin to memory/effector cell transitio n. 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 o f integrin epitope expression on virgin (CD3(+)) T cells (CD45RA(+)/RO (-to+/-)), memory/effector (CD45RA(-)/RO(++)) T cells, and T cells und ergoing the virgin to memory/effector transition: transition region-1 (T1; CD45RA(+to++)/RO(+)); -2 (T2; CD45RA(++)/RO(++)); and -3 (T3; CD4 5RA(+)/RO(++)). Conventional beta 1- and beta 1-integrin epitopes prog ressively 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 t he beta 1 (15/7)- and beta 2 (24)-integrin activation epitopes first a ppears on transitional T cells? and is maintained on a relatively cons tant number of cells (averaging 25-30%) throughout the T1-T3 stages. T hese epitopes are also noted on a subset of activated memory/effector T cells. Importantly, on both transitional and activated memory/effect or 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 ex pression of these epitopes relative to each other is linearly correlat ed, findings strongly supporting the coordinate activation of beta 1 a nd beta 2 integrins during T cell activation in vivo. These results pr ovide the first evidence of integrin activation during an in vivo immu nologic response, and demonstrate the usefulness of mAb recognizing co nformational epitopes and multiparameter flow cytometry in delineating the dynamic interplay of adhesion molecules during complex physiologi c processes.