Antibodies recognizing CD24 LAP epitope on human T cells enhance CD28 and IL-2 T cell proliferation

Membrane expression of the CD24 molecule on activated T lymphocytes is not elucidated fully. We previously described the intracellular and cell-surfac e expression of the CD24 sialic acid-dependent epitope(s) on phytohemagglut inin-activated peripheral blood mononuclear cells, However, the CD24 core p rotein was not detected previously on human T cells, This study reinvestiga ted the expression and role of CD24 in T cell subsets. We analyzed binding of anti-CD24 monoclonal antibodies (mAbs) to sialic and leucine-alanine-pro line (LAP) epitopes in resting and activated, normal T lymphocytes. CD24 LA P and CD24 sialic epitopes were detected on activated CD4- and CD8-positive cells. Although expression of CD24 sialic epitopes remained stably express ed in interleukin (IL)-2-dependent cultures, T cell expression of the LAP e pitope was transient. Anti-LAP antibodies strongly enhanced the response of T cells to a combination of anti-CD3/CD28 mAbs and enhanced proliferative response induced by recombinant IL-2, We found similarities in the tissue d istribution and function of the human CD24 LAP molecule and the murine, hea t-stable antigen, which suggests that CD24 might function as a signaling mo lecule on human T cells.