Expression of activin A in inflammatory arthropathies

The findings that bone marrow fibroblastoid stromal cells are important for activin A production prompted our investigation of activin A expression in fibroblast-like synoviocytes in joint capsule in this and previous studies . In the proliferative reactive synovial membrane obtained from rheumatoid arthritis patients, activin A is detected prominently in the fibroblastoid synovial cells, as well as in the smooth muscle and the endothelial layer o f the arteries in these vascularized proliferative tissues. The concentrati on of activin A in the rheumatoid arthritis synovial fluid was 33.6 +/- 5.0 ng/ml, much higher than the activin A content of osteoarthritis fluid (10. 0 +/- 1.1 ng/ml). Furthermore, our previous studies also showed that inflam matory cytokines, such as interleukin (IL)-1, transforming growth factor (T GF)-beta, interferon (IFN)-gamma, IL-8, and IL-10 markedly enhance the expr ession of activin A mRNA in synoviocytes. These findings are consistent wit h our studies in regard to the regulatory control of activin A production i n bone marrow stroma and monocytes. In addition, the relationship of activi n A to IL-6-induced biological activities in various cell types was also in vestigated. Although activin A has not been directly associated with inflam matory processes, future studies are needed to investigate its production i n response to the accumulated levels of inflammatory cytokines in the synov ium of the patients, as well as the quantitative differences in activin A c oncentrations in many patients with other inflammatory diseases. (C) 2001 E lsevier Science Ireland Ltd. All rights reserved.