VLA‐1: a T cell surface antigen which defines a novel late stage of human T cell activation

The VLA‐1 protein complex defines a previously undescribed very late stage of activated T cell differentiation, following either alloantigen or mitogen activation. This protein appears after 2–3 weeks of activation, considerably later than the early T cell activation antigens such as the interleukin 2 (IL2) receptor, transferrin receptor, 4F2 antigen, T10 and HLA‐DR, and has therefore been termed very late antigen‐1 (VLA‐1). Unlike the IL2 receptor, VLA‐1 expression does not require restimulation with antigen, and in fact, VLA‐1 expression was high on T cells that had lost their IL2 receptors. Expression of VLA‐1 was found on all or nearly all long‐term‐activated T cells including T4+ and T8+ clones, bulk cultures, long‐term T cells from adults and newborns and long‐term T cells maintained in pure or crude IL2 preparations. VLA‐1 was also found on HTLV‐1 infected T cell populations. Immunoprecipitation experiments confirmed that the VLA‐1 protein complex (210000/130000 Mr) can be co‐expressed with another protein complex called VLA‐2 (165 000/130 000 Mr) on the same T cell clones. However, co‐expression was not obligatory because in some long‐term cultures little or no VLA‐2 was present relative to VLA‐1. Because VLA‐1 defines a novel late stage of T cell activation, being present on all or most all types of long‐term activated T cells, and not on any other cell types in peripheral blood, it has unique potential as a marker for activated T cells in vivo and may provide a clue towards elucidating novel long‐term T cell functions or growth requirements of this late stage of T cell differentiation.