Abstract
The alpha1beta1 integrin, very late antigen-1 (VLA-1), is a collagen receptor expressed in many CD4+ T cells localizing to inflamed tissues. Here we show that the expression of VLA-1 is a stable marker of a distinct subset of CD4+ memory T cells. Thus, in human peripheral blood lymphocytes (PBLs), approximately 1-4% of the CD4+ T cells express VLA-1, and following T cell receptor activation ex vivo, the percentage of VLA-1+ cells increases within the CD45RO+ population. Importantly, the activated VLA-1+ and VLA-1- cells can be isolated and maintained in culture as phenotypically stable subsets. Functionally, CD4+ memory T cells, operationally defined as the cells that divide rapidly following stimulation with a recall antigen, are highly enriched for VLA-1+ cells. Moreover, depletion of the small fraction of VLA-1+ cells present in CD4+ PBLs prior to stimulation significantly abrogated the proliferative response to recall antigens. Notably, the VLA-1+ cells in fresh CD4+ PBLs are composed of resting CD45RO+/RA-, CCR7-, CD62L+, CD25-, and VLA-4hi cells. Interestingly, this VLA-1+ subset is enriched for Th1-type cells, and Th1-polarizing conditions during T cell activation favor the emergence of VLA-1+ cells. Thus, VLA-1 expression is a stable marker of a unique subset of human memory CD4+ T cells that predominantly differentiates into Th1 cells.