Streptococcal cell walls and synovial cell activation. Stimulation of synovial fibroblast plasminogen activator activity by monocytes treated with group A streptococcal cell wall sonicates and muramyl dipeptide.

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Abstract
Group A streptococcal peptidoglycan was previously shown to be arthritogenic in rats and has been implicated as a structure present in a class of possible etiologic agents for rheumatoid arthritis. Conditioned medium from human monocytes, after interaction with cell wall sonicates of 4 group A streptococcal strains, was shown here to stimulate the plasminogen activator (PA) activity of nonrheumatoid synovial fibroblasts. Low concentrations of N-acetylmuramyl-L-alanyl-D isoglutamine (muramyl dipeptide) can also generate this synovial activator (SA) activity from human monocytes. The SA activity apparently is distinct from interferon-.gamma., interleukin 1 and interleukin 2. Agents that are arthritogenic in rats evidently can modulate human synovial fibroblast functions via monocytes. The findings are proposed to have possible significance for an understanding of the cellular interactions involved in the formation and function of the rheumatoid pannus, because PA has been invoked as possibly being generally important for the processes of cell migration, tissue remodeling and inflammation.