Correlation of SPE B with histopathologic changes, NO, and cytokine production in a mouse model of Group A streptococcal infection

• Main Authors: Yueh-Hsia Luo, 羅月霞
• Other Authors: Yee-Shin Lin
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/13045438027244421812

碩士 === 國立成功大學 === 微生物暨免疫學研究所 === 89 === The group A streptococci (GAS) Streptococcus pyogenes can cause serious diseases in humans, including streptococcal toxic shock syndrome and necrotizing fasciitis. S. pyogenes secretes various proven or putative virulence factors, e.g., streptococcal pyrogenic exotoxin (SPE) A, SPE B, SPE C, SPE F, and various M proteins, that enable it to invade the host. SPE B, its gene is present in all isolates of S. pyogenes, is the predominant extracellular protein, accounting for up to 95﹪of total secreted proteins. SPE B, which is a cysteine protease, is secreted as a 40-kDa inactive precursor and subsequently cleaved to a 28-kDa molecule. Previous studies in our laboratory by using a mouse model via air pouch inoculation showed that SPE B appeared to be a critical virulence factor in invasive GAS infection. In this study, we further explore the role of SPE B in bacterial growth, invasion, and dissemination, as well as NO and cytokine production. After bacterial inoculation, high levels of SPE B expression were observed in both air pouch exudate and serum at 48 and 72 h. Bacterial growth and dissemination to blood, liver, and kidney were positively correlated with the presence of SPE B. Bacterial numbers in the air pouch exudates from NZ131-infected mice increased at 48 h, while those infected with the speB mutant SW510 were high at 12 h but continuously dropped afterward. Mice may develop bacteremia when infected with NZ131, and bacterial dissemination in spleen, kidney and liver was observed. Bacterial dissemination could not be detected when mice were inoculated with SW510. The histopathological changes in various organs were examined showing mild lesions in kidney and liver in some of the NZ131-infected but not the SW510-infected mice at 24 h. The lesions became more severe in a high percentage of NZ131-infected mice after 48 h. The elevation of BUN, AST and ALT in sera showed a positive correlation with the renal and liver impairment. The production of IL-1b, IL-6, and TNF-a were elevated in sera 12 h after bacterial inoculation then continuously decreased. These pro-inflammatory cytokines in the sera of NZ131-infected mice were higher than those in SW510-infected mice. TNF-a expression was observed in kidney 12 h after inoculation with wild-type bacteria while only low level of TNF-a was observed 72 h after inoculation with speB mutant strain. The expression of iNOS was observed at 12 and 24 h after wild-type bacteria inoculation, vanished at 48 h, and appeared again in a low level at 72 h. The iNOS expression was not observed until 72 h after mutant-type bacteria inoculation. The expression of IL-1b and IL-6 could not be observed in the kidney after bacterial inoculation. Our preliminary results showed that the levels of nitric oxide (NO) in the exudates were elevated after wild-type bacteria inoculation, implicating the involvement of NO during bacterial invasion. Interestingly, subcutaneous injection of recombinant SPE B but not C192S mutant protein caused damage to local endothelial cells, increased vessel permeability, and massive neutrophil influx to local tissue in BALB/c mice. Taken together, SPE B produced during S. pyogenes infection plays a role in bacterial growth and dissemination. SPE B also causes elevation of pro-inflammatory cytokines in the acute phase of bacterial inoculation. These may lead to bacteremia and streptococcal toxic shock syndrome.