Relationship between PGE2 and LTB4 levels in normal and osteoarthritis osteoblasts. Cells were grown to confluence in Ham's F12/DMEM medium containing 10% fetal bovine serum. Confluent cells were incubated for their last 48 hours in serum-free medium containing 1% insulin-transferrin-selenium mix (ITS). Prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) levels were measured with selective ELISA. Data points represent values for individual cell cultures. Low osteoarthritis (OA) and high OA were separated on the basis of their PGE2 levels: high OA had PGE2 levels at least 2 SD above the mean normal PGE2 levels. Normal samples, n = 10; low OA, n = 14; high OA, n = 8.