EFFECT OF GROUP-A STREPTOCOCCAL CYSTEINE PROTEASE ON INVASION OF EPITHELIAL-CELLS

Cysteine protease of group A streptococci (GAS) is considered an impor tant virulence factor. However, its role in invasiveness of GAS has no t been investigated. We demonstrated in this study that two strains of protease-producing GAS had the ability to invade A-549 human respirat ory epithelial cells. Isogenic protease mutants were constructed by us ing integrational plasmids to disrupt the speB gene and confirmed by S outhern hybridization and Western immunoblot analyses. No extracellula r protease activity was produced by the mutants. The mutants had growt h rates similar to those of the wild-type strains and produced normal levels of other extracellular proteins. When invading A-549 cells, the mutants had a two-to threefold decrease in activity compared to that of the wild-type strains, The invasion activity increased when the A-5 49 cells were incubated,vith purified cysteine protease and the mutant . However, blockage of the cysteine protease with a specific cysteine protease inhibitor, E-64, decreased the invasion activity of GAS. Intr acellular growth of GAS was not found in A-549 cells. The presence or absence of protease activity did not affect the adhesive ability of GA S. These results suggested that streptococcal cysteine protease can en hance the invasion ability of GAS in human respiratory epithelial cell s.