Human thy-1: unusual localization and possible functional significance in lymphoid tissues.

BALB/c mice were immunized with purified human brain Thy-1 and used in cell fusion experiments to derive an anti-human Thy-1 monoclonal antibody. Specificity was proven by a) showing that the antigen recognized had precisely the tissue distribution expected of human Thy-1 from previous studies, and b) demonstrating that the molecule purified from human brain by monoclonal antibody affinity columns 1) had the same mobility on SDS PAGE as pure rat Thy-1 and 2) could inhibit an assay previously shown to be directed at the human-rat cross-reactive component of Thy-1. Studies with the fluorescence-activated cell sorter confirmed that Thy-1 is absent from human blood lymphocytes and cell suspensions from human lymphoid organs, except that very weak fluorescence could be detected on 7% of thymus cells in suspension. However, fluorescence studies on frozen sections showed bright staining restricted mainly to the periphery of the thymus lobule, the marginal zone and some periarteriolar lymphocytes in the spleen, and the post-capillary venules of lymph node. In some lymph nodes, a halo of Thy-1 positive cells was seen around lymphatic nodules or germinal centers, but this was not a constant finding. This distribution is different from the known distribution of Thy-1 in the lymphoid tissues of the mouse and rat. Our studies suggest that human Thy-1 might be involved in lymphocyte recirculation, and that it is a marker for early T lymphocytes in man. The studies also show that the few Thy-1 positive cells in human lymphoid organs are selectively lost in the preparation of single-cell suspensions.