CLONING OF MOUSE OX40 - A T-CELL ACTIVATION MARKER THAT MAY MEDIATE T-B-CELL INTERACTIONS

A cDNA library was prepared from the murine Th cell line Th2 D.10 and used to clone the murine homologue of Ox40 by polymerase chain reactio n. Comparison of the mouse sequence with the rat revealed greater than 90% homology between the two sequences at both the DNA and protein le vel. Northern blot analysis found that, as in the rat, Ox40 expression appears to be restricted to activated T cells. A chimeric receptor gl obulin was prepared to include the mouse Ox40 extracellular domain cou pled to the hinge-CH2-CH3 domains of human IgG1 (Ox40-Ig). This solubl e form of the molecule was then used to identify cells bearing a ligan d for Ox40. FACS analysis revealed that Ox40-Ig bound to a subset of p eritoneal B cells as well as to a fraction of LPS-activated splenic B cells. Immunostaining of spleen sections using an Ag-specific conjugat e and Ox40-Ig found a significant proportion of antibody-forming cells co-stained with Ox40-Ig. Immunoprecipitation of cell-surface radiolab eled peritoneal B cells suggests a specific interaction with a protein of 70 kDa.