Comparison of the anti-arthritic effects of recombinant TRAIL (rTRAIL) with those of adenoviral-mediated gene transfer of TRAIL. Arthritic rabbit knee joints, induced by intra-articular injection of IL-1β producing cells, were injected intra-articularly with 20 μg of rTRAIL per knee or saline as well as 1 × 1011 particles of adenoviral membrane bound murine TRAIL (Ad-mTRAIL) vectors or adenoviral Lac Z (Ad-LacZ) vectors. The rabbits were sacrificed 48 h post-injection and the joint capsules sectioned to evaluate synovitis. Histological examination of hematoxylin and eosin (H&E) stained synovium sections are shown for saline, rTRAIL, Ad-mTRAIL and Ad-LacZ treated knees. Synovial sections analyzed by TUNEL staining are shown for saline, rTRAIL, Ad-TRAIL and Ad-Lac Z treated joints (200×). Examples of apoptotic cells are indicated by the arrows.