Enzyme histochemical studies of the homogeneity of the mononuclear phagocyte system with special reference to the synovium.

The cytogenetic relationship between synovial lining cell type A and macrophages both involved in joint destruction is still obscure. By means of enzyme histochemistry we tried to demonstrate marker enzymes of macrophages, like non-specific esterase and acid phosphatase in lining cells of normal and arthritic rats too. The pattern of esterase-positive cells depends on the arrangement of the lining cell layer. In flat layers single cells and in compact layers the upper row of cells react positively. The activity of acid phosphatase is negligible as compared with macrophages in liver, lung, or spleen. In arthritic joints acid phosphatase of lining cells increases and non-specific esterase concomitantly decreases. In the subsynovial tissue large amounts of esterase-positive cells occur. In these enzyme histochemical studies the pattern of marker enzymes may be indicative for a population of macrophages within the lining cell layer still under normal conditions.