Expression of gp34 (OX40 ligand) and OX40 on human T cell clones

gp34, which we previously cloned, is a ligand of OX40 (CD134), a costimulat ory molecule involved in T cell activation. To elucidate the role of human OX40/OX40L interaction, we examined the expression of gp34 (OX40L) and OX40 in normal human hematopoietic cells by using flow cytometry, OX40 expressi on is observed on activated T cells, while OX40L is expressed in antigen-pr esenting cells. However, cytotoxic T lymphocyte (CTL) clones specific for E pstein-Barr virus (EBV)transformed autologous lymphoblastic cell lines (LCL s) induced both OX40 and OX40L expression after antigen or T cell receptor (TCR) stimulation, This study suggests a possible function of OX40L/OX40, t hrough T cell-T cell interaction, in the reactivation of memory T cells in an autocrine manner, with implications for the pathogenesis of viral infect ions and neoplasms.