INHIBITION OF HUMAN PERIPHERAL-BLOOD MONONUCLEAR CELL-PROLIFERATION BY STREPTOCOCCUS-PYOGENES CELL EXTRACT IS ASSOCIATED WITH ARGININE DEIMINASE ACTIVITY

Streptococcus pyogenes (group A Streptococcus) cell extracts (CE) have a remarkably powerful and dose-dependent inhibitory effect on antigen , superantigen, or mitogen-stimulated human peripheral blood mononucle ar cell (PBMC) proliferation in vitro. Purification of the inhibitory component present in S. pyogenes type M5 (Manfredo strain) CE by anion -exchange chromatography followed by gel filtration chromatography sho wed that the inhibitor had an approximate native molecular mass of 100 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of pur ified inhibitory fractions followed by silver staining gave a single b and with an approximate molecular mass of 47 kDa, indicating that the inhibitor is composed of two identical subunits. NH2-terminal sequenci ng of the protein revealed that it was identical to the previously cha racterized streptococcal acid glycoprotein (SAGP); this protein posses ses between 31.5 and 39.0% amino acid identity with arginine deiminase (AD) from Mycoplasma hominis, Mycoplasma arginini, Pseudomonas putida , and Pseudomonas aeruginosa. AD enzyme activity was present in unfrac tionated CE prepared from a range of streptococcal strains, and partia lly purified inhibitory fractions of Manfredo CE also had high levels of activity. The inhibitory effect of Manfredo CE was overcome by the addition of L-arginine to proliferation assays in which human PBMC wer e stimulated with phytohemagglutinin. We conclude that SAGP, or its ho molog, possesses AD activity and that the potent inhibition of prolife ration of human T cells by streptococcal CE: is due to activity of thi s enzyme.