Following onset of arthritis, mice were treated with either PPI-2458 (1.5 mg/kg every other day), soluble tumour necrosis factor receptor (sTNF-R)II (5 mg/kg every other day), or vehicle alone for 28 days. Hematoxylin and eosin sections were scored in a blinded manner for pannus formation, synovitis, bone and cartilage erosion. Paws were assigned one of four grades: normal; mild synovitis with some loss of cartilage; moderate with more extensive synovial hyperplasia, destruction of cartilage and some bone erosions caused by an invasive pannus front; and finally severe, judged to have complete destruction of the joint architecture. Results are the number of paws exhibiting normal, mild, moderate and severe changes, with percentage in parentheses. Statistical analysis of raw data was carried out by χ2 test versus untreated mice.