Immunotherapeutic advances in the treatment of gram-negative bacterial sepsis

Reduction of circulating prostaglandin E2 level by antiserum against core lipopolysaccharide in a rabbit model of multiple organ failure

OBJECTIVE

To determine the potential role of prostaglandin E2 (PGE2) in the development of multiple organ dysfunction or failure (MOF), the possible effects of antiserum directed against Re chemotype lipopolysaccharide (LPS, from Re mutant of Escherichia coli F515) on circulating PGE2 level and survival rate, and whether there is an elevation in the plasma LPS concentration that could account for the induction of arachidonic acid metabolite in a rabbit model of MOF caused by acute hypovolemic insult.

DESIGN, MATERIALS, AND METHODS

An animal model of MOF in rabbits, engendered by feeding live Escherichia coli O111:B4 before hemorrhagic shock (35-40 mm Hg for 60 min), was used in the present study. Re-LPS antiserum was given intravenously in the treatment group at the onset of hemorrhage and 4 hours after resuscitation. The animals that received equal volumes of normal rabbit serum and antiserum served as the control group.

MEASUREMENTS AND MAIN RESULTS

The circulating PGE2 level was not increased at the end of shock (p > 0.05), but it was found to be significantly elevated 24 hours after hemorrhage and resuscitation in both groups. However, Re-LPS antiserum administration markedly decreased peak PGE2 level (p < 0.05) and attenuated multiple organ damage caused by acute insult. Concomitantly, there were also lower LPS concentrations in the treatment group as compared with the control group (p < 0.05-0.01). The survival rate was significantly increased in antiserum-treated rabbits 96 hours postinjury (treatment vs. control: 58.0% vs. 11.1%, p < 0.01).

CONCLUSIONS

The results suggest that an excessive generation and release of PGE2 may be involved in the pathogenesis of immunosuppression and MOF following hemorrhage and resuscitation. Re-LPS antiserum has an inhibitory effect on overproduction of circulating PGE2 and the ability to improve survival with MOF. Gut-derived endotoxemia, bacterial translocation, or both, could account, at least in part, for the PGE2 formation and release in animals response to acute hypovolemic insult.

Use of novel therapeutic agents for the treatment of serious infection

The use of biologic reagents directed against invading microbes and deleterious aspects of the host response is presently under intense investigation. The development and use of these reagents have contributed significantly to our understanding of the host response to infection, and they probably represent the first true foray into the area of immunotherapeutic manipulation. Thus, the effects of the administration of anti-endotoxin and antitumor necrosis factor-alpha monoclonal antibodies and the interleukin-1 receptor antagonist are being examined in large-scale clinical trials, and tumor necrosis factor-binding protein and bactericidal/permeability-increasing protein also may undergo clinical testing. Much controversy has already arisen regarding the manner in which these therapeutic reagents will be best utilized. The enormous amount of information that has already been obtained concerning the use of these reagents assuredly will contribute significantly to our understanding of the diagnosis and treatment of serious infection and will set the stage for the development and appropriate testing of additional new diagnostic and therapeutic reagents during the current decade.

Anti-endotoxin monoclonal antibodies inhibit secretion of tumor necrosis factor-alpha by two distinct mechanisms

OBJECTIVE

To determine whether monoclonal antibodies (mAbs) directed against lipopolysaccharide (LPS, endotoxin) act by promoting LPS neutralization, LPS uptake by macrophages, or both processes, the authors assessed the effects of these agents on LPS-induced cytokine secretion and cellular uptake of LPS.

SUMMARY BACKGROUND DATA

MAbs directed against LPS have been shown to attenuate LPS-induced macrophage tumor necrosis factor-alpha (TNF-alpha) secretion, a process that may contribute to protective capacity. The mechanisms by which this process occurs have not been established.

METHODS

MAbs directed against LPS were evaluated in vitro for their capacity to (1) inhibit TNF-alpha secretion, and (2) alter fluorescein isothiocyanate-labeled LPS uptake (employing flow cytometry analysis and fluorescence microscopy) by the macrophage-like cell line RAW 264.7.

RESULTS

MAb 8G9, an IgG3 directed against the O-antigen polysaccharide region of Escherichia coli 0111:B4 LPS, significantly reduced LPS-induced TNF-alpha secretion and promoted a more than 40-fold increase in LPS uptake by macrophages. The authors established that this was mediated by a Fc receptor-mediated process because 8G9 F(ab')2 fragments that lack the Fc portion of the IgG molecule were capable of inhibiting TNF-alpha secretion, but did not promote increased LPS uptake to the same degree. Cross-reactive, anti-deep core/lipid A mAb 1B6, an IgG2a, also promoted uptake of E. coli 0111:B4 LPS and O-antigen polysaccharide-deficient E. coli J5 LPS, but only inhibited TNF-alpha secretion induced by E. coli J5 LPS to which it binds most efficiently. MAb 3D10, an IgM also directed against the O-antigen polysaccharide region of E. coli 0111:B4 LPS, inhibited TNF-alpha secretion but did not increase cellular uptake of LPS, presumably acting solely due to LPS neutralization. Polymyxin B, an antibiotic that binds stoichiometrically to the lipid A portion of LPS, inhibited TNF-alpha secretion and prevented cellular LPS uptake.

CONCLUSIONS

These results suggest that IgG and IgM anti-LPS mAbs exert protective capacity by extracellular neutralization of LPS, while IgG Fc receptor-mediated cellular uptake also may serve to bypass macrophage activation and TNF-alpha secretion by promoting internalization and intracellular neutralization.

Cross-reactive murine monoclonal antibodies directed against the core/lipid A region of endotoxin inhibit production of tumor necrosis factor

Two murine monoclonal antibodies (mAbs) directed against the core/lipid A moiety of lipopolysaccharide (endotoxin, LPS) were derived from mice immunized with either Escherichia coli J5 or Salmonella minnesota Ra, Rb, Rc, or Re heat-killed organisms or LPS. These mAbs were selected on the basis of their ability to cross-react against a panel of gram-negative bacterial LPS using Western immunotransblot analysis. We hypothesized that these anti-LPS mAbs directed against the conserved core region of LPS would inhibit LPS-induced macrophage tumor necrosis factor (TNF) production by neutralizing LPS derived from different gram-negative bacteria. To test this hypothesis, unelicited peritoneal macrophages were treated with either mAb 5G11 (deep core/lipid A specificity, broad LPS cross-reactivity) or mAb 5B11 (intermediate core specificity, limited LPS cross-reactivity). Macrophages were then challenged with a panel of LPS, and TNF activity was measured by the use of the L929 cytotoxicity assay. MAb 5G11 significantly inhibited TNF production against a panel of different types of LPS, but mAb 5B11 did not. In addition, mAb 5G11 did not inhibit TNF production due to isolated lipid A stimulation, suggesting that mAb 5G11 neutralized LPS by binding primarily to the deep core region of LPS. MAb 5G11 was also able to inhibit TNF production if added within 10 min of LPS stimulation but had no effect at 30 min, suggesting that macrophage stimulation may be irreversible during even the early stages of the response to LPS.(ABSTRACT TRUNCATED AT 250 WORDS)

Modern approaches to the therapy of septic shock

Bacteremia from gram-negative rods is a great cause of concern for hospital physicians today. Shock-complicating gram-negative sepsis has a mortality rate of 60% and above, despite early diagnosis and treatment. Intensive research efforts have shown new pathophysiological mechanisms and mediators involved in septic shock, with changes in recommended treatment protocols. In this report, the authors review the use of corticosteroids, fibronectin, naloxone hydrochloride, and immunotherapy, with emphasis on theoretical considerations and relevant clinical experience. Although these treatment methods may have been promising initially, data from large double-blind human trials are either lacking or unencouraging. While continued research and modern therapeutic approaches should improve future survival rates from septic shock, use of the therapies reviewed should be considered experimental at this time.