Western blots of synovial fluid samples. Representative western blots of a synovial fluid sample obtained (a), (b) from a grade 0 normal asymptomatic organ donor or (c), (d) from a patient with rheumatoid arthritis using an anti-mature osteogenic protein 1 (OP-1) antibody (MAB354) demonstrating the pro-form and mature form of OP-1 protein. (a) and (c) Nonreduced conditions, (b) and (d) reduced with β-mercaptoethanol. (a) and (b) Sample was loaded at different dilutions of sample buffer in the amount of 30 μl/lane: lane 1, 1:1000; lane 2, 1:100; lane 3, 1:10; and lane 4, 1:5. (c) and (d) Undiluted sample was digested with the following enzymes and then loaded onto each lane at 30 μg protein: lane 1, control, no treatment; lane 2, hyaluronidase (50 units/ml); lane 3, chondroitinase ABC (0.1 U/ml); lane 4, combination of hyaluronidase (50 units/ml) and chondroitinase ABC (0.1 U/ml). The numbers on gels represent the size of the protein bands of interest.