Antibody to the E3 glycoprotein protects mice against lethal venezuelan equine encephalitis virus infection.

Six monoclonal antibodies were isolated that exhibited specificity for a furin cleavage site deletion mutant (V3526) of Venezuelan equine encephalitis virus (VEEV). These antibodies comprise a single competition group and bound the E3 glycoprotein of VEEV subtype I viruses but failed to bind the E3 glycoprotein of other alphaviruses. These antibodies neutralized V3526 virus infectivity but did not neutralize the parental strain of Trinidad donkey (TrD) VEEV. However, the E3-specific antibodies did inhibit the production of virus from VEEV TrD-infected cells. In addition, passive immunization of mice demonstrated that antibody to the E3 glycoprotein provided protection against lethal VEEV TrD challenge. This is the first recognition of a protective epitope in the E3 glycoprotein. Furthermore, these results indicate that E3 plays a critical role late in the morphogenesis of progeny virus after E3 appears on the surfaces of infected cells.

Proinflammatory mediators of toxic shock and their correlation to lethality.

Bacterial exotoxins and endotoxins both stimulate proinflammatory mediators but the contribution of each individual toxin in the release of mediators causing lethal shock is incompletely understood. This study examines the cytokine response and lethality of mice exposed to varying doses of staphylococcal enterotoxin B (SEB) or lipopolysaccharide (LPS) and their combinations. In vivo, SEB alone induced moderate levels of IL-2 and MCP-1 and all mice survived even with a high dose of SEB (100 microg/mouse). LPS (80 microg/mouse) caused 48% lethality and induced high levels of IL-6 and MCP-1. SEB induced low levels of TNFalpha, IL-1, IFNgamma, MIP-2, and LPS synergized with SEB in the expression of these cytokines and that of IL-6 and MCP-1. Importantly, the synergistic action of SEB and LPS resulted in lethal shock and hypothermia. ANOVA of cytokine levels by survival status of SEB-plus-LPS groups revealed significantly higher levels of TNFalpha, IL-6, MIP-2, and MCP-1 in nonsurvivors measured at 8 hours. Significantly higher levels of IFNgamma and IL-2 were observed at 21 hours in nonsurvivors of toxic shock compared to those in survivors. Overall, synergistic action of SEB and LPS resulted in higher and prolonged levels of these key cytokines leading to toxic shock.

Central roles for IL-2 and MCP-1 following intranasal exposure to SEB: a new mouse model.

Murine models for bacterial superantigens like staphylococcal enterotoxin B (SEB) have to date been rather cumbersome. The reasons include: (1) necessary use of potentiating agents such as actinomycin D, d-galactosamine, lipopolysaccharide (LPS), or viruses; (2) high toxin amounts required to elicit effects; and/or (3) generation of phenotypic-stable transgenic animals. Our study employed readily available C3H/HeJ (TLR4 negative, LPS-nonresponsive) mice with intranasal and intraperitoneal administration of low microgram quantities of SEB. These animals responded to SEB with severe lung inflammation and hypothermia, culminating in death. A survey of cytokines/chemokines in sera and lungs after lethal intoxication revealed that monocyte chemoattractant protein-1 and interleukin-2 were associated with effects in this model. In contrast, SEB had minimal effects upon congenic (TLR4 positive, LPS-responsive) C3H/OuJ mice. Lethality of SEB in C3H/HeJ mice was neutralized with SEB-specific antibodies, suggesting potential utility of this model for future therapeutic studies.

Critical timing, location and duration of glucocorticoid administration rescue mice from superantigen-induced shock and attenuate lung injury.

Bacterial superantigens, such as staphylococcal enterotoxin B (SEB), are major virulence factors implicated in the pathogenesis of toxic shock. In this study we investigated the efficacy of glucocorticoid therapy in preventing SEB-induced lethal shock initiated through the respiratory route in mice. Dexamethasone, a potent anti-inflammatory steroid, administrated intranasally on the first day, followed by intraperitoneal doses on the subsequent 4 days, was effective in attenuating SEB-induced hypothermia, and reduction in systemic and pulmonary proinflammatory mediator release. This optimal dosing and schedule of glucocorticoid treatment mitigated lung inflammation and resulted in 100% survival in this intranasal mouse model of SEB-mediated shock.