Differential expression of membrane polypeptides on fetal thymic stroma co-cultured with bone marrow cells from young and old mice.

Cell membrane polypeptides from co-cultures of lymphocyte depleted fetal thymuses (C57BL/Ka, H-2b, Thy 1.1) and bone marrow (BM) cells (C57BL/6J, H-2b, Thy 1.2) were analyzed by two-dimensional gel electrophoresis (2D-PAGE). Donors of BM cells were young (3 months) and old (24 months) mice. Two polypeptides, not detected in either the alymphoid thymus itself or the BM cells prior to seeding, were expressed in the co-cultures, and their levels in the presence of old BM cells were higher than in the presence of young BM cells. Two other polypeptides, originally observed in the thymic stroma, exhibited reduced levels by day 3 in cocultures containing BM cells from young donors, but not from old donors. It is concluded that distinct changes in membrane proteins are manifested in the thymic stroma, as well as in the colonizing BM cells.