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 (IL 2) 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 (210 000/130 000 M,) can be co-expressed with another protein complex called VLA-2 (165 000/130 000 M,) on the same T cell clones. However, co-expression was not obligatory because in some longterm 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. Perhaps the most significant aspect of the discovery of VLA-1 and VLA-2 will be to provide the means for further investigating these previously uncharacterized stages of T cell differentiation.
W e thank Ed Luther for establishing T4' and T8' lines by cell sorting,
J. McLean for assistance with T cell clones and lines and Joyce Culgin
for clerical assistance.