Lipoxygenase enzymes in rheumatoid arthritis and osteoarthritis synovial tissue. 5-Lipoxygenase (5-LO) and 15-LO-1 enzymes are present in both rheumatoid arthritis (RA) and osteoarthritis (OA) synovial tissue. Photographs illustrating brown (diaminobenzidine) immunoperoxidase staining for (a, b, c) 5-LO and (d, e, f) 15-LO-1 in sections from frozen synovial biopsies of (a, b, e) RA and (c, f) OA patients (hematoxylin counterstained). (d) Bronchial epithelium staining positive for 15-LO-1. Insets: (a) RA synovium stained with 5-LO antibody and (d) bronchial epithelium stained with 15-LO-1 antibody, preabsorbed with purified 5-LO and 15-LO-1 protein, respectively. Original magnification: ×100 (a, d and insets) and ×200 (b, c, e, f).