Effects of interaction between Escherichia coli verotoxin and lipopolysaccharide on cytokine induction and lethality in mice.

In Escherichia coli 0157 infections, verotoxins (VT) play a critical role in causing the disease, although other factors such as lipopolysaccharide (LPS) and inflammatory cytokines may affect the progression and course of the disease. The present study examined the roles of VT and LPS in induction of serum cytokines and lethality in mice. LD50 of VT2 (13 ng) was c. 10(4)-fold smaller than that of LPS (400 microg). Although the lethal toxicity of these toxins was examined in several experimental conditions, such as VT2 (5, 10, 20, 40 ng/mouse) alone or in combination with LPS (100 microg/mouse) at various times (-2 days to +2 days), no evidence of synergy was observed. VT2 did not augment LPS-induced tumour necrosis factor-alpha (TNF-alpha) or interleukin-6 production, and conversely suppressed TNF-alpha production when it was injected 2 days before LPS challenge. The data failed to indicate either synergic or additive effects of VT and LPS on cytokine production or lethality in mice. In contrast, antagonistic interactions were clearly observed in cytokine production in certain conditions. The results suggested that these toxins may be co-operatively involvedin the pathology of VT-related diseases, but not through synergic interactions.

Factors affecting the course and severity of transnasally induced Staphylococcus aureus pneumonia in mice.

In order to examine several factors that may affect the course and severity of transnasally induced Staphylococcus aureus pneumonia in mice, bacteria were prepared in a free suspension or bound to fetal mouse cells. Immunosuppression was induced in five strains of mice (ICR, C57BL/6, BALB/c, C3H/He and CBA/J) by injection of cyclophosphamide (200 mg/kg body weight), 2 days before infection. Impairment of mucociliary clearance was induced by intranasal instillation of formalin. Mice were then infected with various doses and strains of the organism. Although no significant differences were observed between either form of inoculum, pretreatment with formalin plus cyclophosphamide was associated with a significant increase in lung bacterial counts. In particular, cyclophosphamide treatment was associated with a high mortality in mice infected with several strains of S. aureus irrespective of their toxin production profiles. Histopathological examination demonstrated that in mice treated with formalin plus cyclophosphamide, clusters of bacteria were observed in lung parenchyma, associated with a mild accumulation of inflammatory cells at day 2 and extensive cell infiltration at day 7. CBA/J mice represented the most susceptible strain among those examined, with 10(4)- and 10(2)-fold higher bacterial counts in the lungs at days 3 and 5, respectively. These results indicate that neutropenia and impaired mucociliary clearance are major factors that influence the severity of S. aureus pneumonia in mice. Analysis of the role of genetic background in enhancement of vulnerability to infection is warranted in future studies.