On the other hand, mice treated with 50 g SEB+500 g Ch 82 M+500 g Ch 63 appeared normal, were sleek of coat, energetic and mobile (Fig. vitro. In thein vivomodel of lethal toxic shock syndrome (TSS) in HLA-DR3 transgenic mice, two of these antibodies conferred significant partial protection when administered individually, but offered complete protection in a synergistic manner when given with each other. Similarly,in vivo,lovastatin alone conferred only partial protection from TSS much like single anti-SEB antibodies. However, used in combination with one chimeric neutralizing anti-SEB antibody, lovastatin provided complete protection against lethal TSS in HLA-DR3 transgenic mice. These experiments demonstrate thatin vivoprotection against lethal doses of SEB can be achieved by a statin of confirmed clinical security and chimeric human-mouse antibodies, brokers now widely used and known to be of low immunogenicity in human hosts. == Introduction == Staphylococcal enterotoxin B (SEB) is a potent exotoxin secreted byStaphylococcus aureusthat causes life-threatening toxic shock syndrome (TSS)[1],[2],[3],[4],[5]and food poisoning[6]. Resistant to denaturation, readily produced by recombinant DNA technology and highly toxic (LD50in humans estimated to be nanograms/kg[7],[8]), SEB is usually classified as a priority B bioterrorism agent. A superantigen, SEB binds to both MHC-II on antigen presenting cells (APCs) and to TCRs incorporating particular V chains on T-cells[2],[3],[4],[9],[10]. The toxin can trigger up to 20% of T-cells resulting in the induction of high levels of proinflammatory cytokines, including IL-2, IFN-, and TNF- derived from TH1 cells[1],[2],[3],[11],[12],[13]and IL-1 and TNF- from activated APCs[14],[15],[16]. Its action is initiated by an extracellular phase in which toxin engages the Metanicotine TCR, thereby triggering intracellular signal transduction processes that result in T-cell activation. Several approaches to preventing the formation of MHC- II/SAg/TCR complexes have been explored and include induction of anti-SEB antibodies by immunization with proteosome-SEB toxoid vaccines[17],[18], inactivated recombinant SEB vaccine[19],[20],[21], and synthetic peptides[22], IVIG for passive immunoprophylaxis and immunotherapy[23],[24],[25],[26], peptide antagonists[12],[27],[28], and synthetic chimerically linked mimics of SEB-binding regions of class II and TCR[29],[30],[31]. Engineered mimics of TCR V[32]that block SEB activationin vitroand show promising results when testedin vivoin a rabbit model have been reported[32]. However, these mimics were reported to have short half-lives (325 moments in rabbits) and their test in human MHC-II transgenics, a robust animal model that mimics human TSS[33],[34],[35],[36],[37],[38]has not yet been reported. Despite these efforts, at present there is no curative treatment for SEB-induced TSS, no practical prophylaxis and no antidote for intoxication following accidental or malicious exposure. The mortality rate varies from 4 to 22% and clinical treatment is currently focused on supportive steps, targeted antibiotic therapy, and adjunctive Metanicotine immunomodulatory therapy[39]. We Metanicotine recently generated high affinity human-mouse chimeric monoclonal antibodies (MAbs) against SEB. We have shown that these antibodies are capable of neutralizing SEBin vitro, and attenuate SEB-induced immune activationin vitro[40]. Subsequent to our report, there have been studies describing the generation of additional anti-SEB antibodies[41],[42]. More recently, Varshney et al., explained the generation and characterization of murine monoclonal antibodies with neutralizing and protecting abilities against SEB-induced lethal shock (SEBILS)[43]. In the current study we establish the neutralizing potential of our human-mouse chimeric antibodiesin vivoand also show that our chimeric anti-SEB antibodies are able to protect from lethal SEB-induced TSS in a more robust HLA-DR3 transgenic mice model. In addition, we examined the possibility that an intracellular inhibitor of ERBB T-cell activation and cytokine signaling would complement the inhibitory effect of extracellularly acting anti-SEB antibody. As an intracellular inhibitor of SEB-induced signal transduction processes, we used lovastatin, and found this statin inhibited T-cell activation just as the structurally similar simvastatin has been shown to do[44]. Lovastatin (Mevacor) is usually widely used in clinical practice and is known to have low toxicity in humans[45]. In addition to their well known role in reduction of cholesterol levels, statins are known also to have anti-inflammatory and immunomodulatory properties[44],[46]. Simvastatin is usually reported to inhibit SEB-mediated T-cell activation in human peripheral blood[44], and atorvastatin enhances T-cell differentiation from TH1 to TH2[47]. Statins also inhibit cytokine-mediated signaling pathways[48]. == Results == == Chimeric Anti-SEB Antibodies Protect Mice from SEB-induced TSS More Effectively in Combination than Alone == In our previous report, we recognized a pair of high affinity, non-crossreacting, and SEB-neutralizing mouse MAbs and.