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Synthetic muramyl dipeptide (MDP) could stimulate skin fibroblasts of the guinea pig to produce thymocyte-activating factor, which augments the proliferative response of thymocytes to phytohemagglutinin (PHA). Adjuvant-active analogues of MDP also stimulated fibroblasts to produce the factor, whereas adjuvant-inactive analogues failed to do so. Thus a marked parallelism was found between adjuvant activity of these compounds and the stimulating effect on fibroblasts. Thymocyte- activating factor derived from MDP-stimulated fibroblasts was found in the fraction of mol wt 30,000-60,000 by gel filtration on a Sephacryl S- 200 column. Furthermore, this factor did not exhibit T cell growth factor activity.

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TETSURO IKEBE, HIDEAKI IRIBE, MASATO HIRATA, FUMI YANAGA, and TOSHITAKA KOGA Muramyl dipeptide, an essential structure for the diverse biologic activities of bacterial cell wall peptidoglycan, inhibited the synthesis of glycosaminoglycad proteoglycan in cultured rabbit costal chondrocytes in a dose-dependent manner. Muramyl dipeptide, as well as lipopolysaccharide and interleukin-la, also enhanced the release of MS-sulfate-prelabeled glycosaminoglycad proteoglycan from the cell layer, which seems to reflect, at least partially, the increasing degradation of glycosaminoglydproteoglycan. Five synthetic analogs of muramyl dipeptide known to be adjuvant active or adjuvant inactive were tested for their potential to inhibit synthesis of glycosaminoglycadproteoglycan and to enhance the release of glycosaminoglydproteoglycan in chondrocytes. The structural dependence of these synthetic analogs on chondrocytes was found to parallel that of immunoadjuvant activity. These results suggest that muramyl dipeptide is a potent mediator of catabolism in chondrocytes.