Origin of synovial type A cells during inflammation. An experimental approach.

Antigen-induced hypersensitivity arthritis in guinea pigs leads to histopathological changes in the synovial membrane similar to those seen in rheumatoid arthritis. Until recently, the characteristic lining-cell hyperplasia was believed to be mainly due to proliferation of synoviocytes. The validity of this hitherto predominating concept might be refused by our experimental cell-kinetic data, which demonstrate a pronounced participation of cells of the bone marrow-derived mononuclear phagocyte system in inner multilayer formation of the inflamed synovium. This view of the response of the synovium as a bone marrow-dependent reaction is strongly supported by whole-body irradiation experiments, which indicated that hyperplasia of the lining cell of the synovium is absent in animals with an induced cell depletion of the bone marrow.