IDENTIFICATION OF RAT OX40 LIGAND BY MOLECULAR-CLONING

OX40 (CD134) is a member of the tumor necrosis factor (TNF) receptor s uperfamily first identified as a rat T cell activation marker. In the present study, we identified the rat Ligand for OX40 (OX40L) by molecu lar cloning. Rat OX40L cDNA was cloned from a HTLV-1-transformed rat T cell line by cross-hybridization with mouse OX40L cDNA. The predicted rat OX40L polypeptide is composed of 199 amino acids, showing 80.9 an d 43.3% homology to mouse and human OX40L, respectively. Expression of rat OX40L mRNA was found in HTLV-1-transformed rat T cell lines. Expr ession of OX40L on the cell surface of these HTLV-1-transformed rat T cell lines was also demonstrated by flow cytometric analysis with a so luble fusion protein composed of the extracellular region of the Fc po rtion of human IgG (OX40-Ig). To explore the function of rat OX40L, we generated cDNA transfectants stably expressing rat OX40L. The rat OX4 0L transfectants exhibited a potent costimulatory activity for prolife ration and IL-2 production of anti-CD3-stimulated rat T cells. These r esults indicated that rat OX40L can provide an efficient costimulation for rat T cells and that it may be involved in HTLV-1-associated path ologies in the rat system as has been suggested in the human system. ( C) 1998 Academic Press.