CD45 PARTIALLY MEDIATES HETEROTYPIC ADHESION BETWEEN MURINE LEUKEMIA LYMPHOMA CELL-LINE L5178Y AND MARROW STROMAL CELLS/

We raised mAbs to whole L5178Y leukemia/lymphoma (LL) cells to identif y adhesion proteins involved in adherence between LL cells and marrow stromal cells. One mAb, 4C, and its subclones 4C.1 and 4C.2 inhibited adherence of L5178Y LL cells to MLT, a nontransformed murine marrow st romal cell line. These MoAbs are directed against CD45RA. Control anti -CD45 mAbs and isotype mAbs were non-inhibitory. Other anti-CD45 mAbs, M1/9.3, RA3-3A1/6.1 and RA3-2C2/1 do not compete with mAb 4C.1 for bi nding to the L5178Y cell surface, but mAb 4C.1 competes for binding of mAb RA3-2C2/1. Effects of mAb 4C on tyrosine-phosphatase activity of CD45 in L5178Y cells are minimal, suggesting direct involvement of CD4 5 as an adhesion protein. (C) 1998 Elsevier Science Ltd. All rights re served.