CD45RA T-cell activation without proliferation by a partial agonist monoclonal antibody to β1 integrin

CD45RA T cells are fully co-activated by natural beta 1 integrin ligands fibronectin (FN) and VCAM-1, as well as monoclonal antibody (mAb) 19H8, which binds a combinatorial epitope of the alpha 4 beta 1 heterodimer. These integrin ligands stimulate CD3-dependent proliferation and the upregulation of early activation markers CD25 and CD69. However, beta 1-specific antibody 33B6, which binds to a similar range of the predominant T-cell integrins as natural ligands FN (alpha 4 beta 1 and alpha 5 beta 1) and VCAM-1 (alpha 4 beta 1), failed to costimulate proliferation in the CD45RA subset, while retaining the ability to costimulate early activation markers CD25 and CD69. After addition of exogenous human interleukin-2 to the culture media, 33B6 costimulation of proliferation is restored. These data provide evidence that a branch of the alpha 4 beta 1 integrin-signaling pathway in CD45RA T cells can be independently regulated and exploited through the use of partial agonist ligands, including mAbs to the integrin heterodimer.