Effect of active and passive immunizations with lipid A and salmonella minnesota Re 595 on gram-negative infections in mice

Review: Evidence against the hypothesis that antibodies to the inner core of lipopolysaccharides in antisera raised by immunization with enterobacterial deep-rough mutants confer broad-spectrum protection during Gram-negative bacterial sepsis

Antisera to rough enterobacterial mutants of chemotypes Ra, Rc, and Re have been reported to confer broad-spectrum protection against wild-type smooth strains. It has been hypothesized that binding and neutralization of lipopolysaccharides (LPS) by antibodies to common core epitopes underlies such protection. This review summarizes experiments by our laboratory and others that do not confirm this concept and proposes reasons for the divergent results. Studies indicating broad-spectrum protection by rough-mutant antisera often had defects in experimental design or methodology. These include the failure: (i) to use matched pre- and postimmune sera from the same donors to control for variable protective activity of normal sera; (ii) to exclude the role of natural and polyclonally stimulated antibodies with proven protective activity against the infecting bacterial strain (e.g. O-specific, capsular, Pseudomonas exotoxin A); (iii) to exclude protective effects of acute-phase serum factors; (iv) to exclude protective effects of endotoxin contamination after adsorption or fractionation of antibody preparations; (v) to use non-boiled bacteria and LPS not subjected to acid-hydrolysis or gel-fractionation, and to exclude nonspecific adsorption, to demonstrate physiologically meaningful binding of rough-mutant antibodies to smooth enterobacteria and their LPS.

Immunotherapy of endotoxemia and septicemia

Neutralization of endotoxin (lipopolysaccharide, LPS) would be of considerable benefit in the treatment of Gram-negative sepsis. Administration of anti-LPS antibodies is an old approach which has been renewed by improvements in monoclonal antibody technology. The antibodies directed at the conserved core region of LPS or at the lipid A which have been studied in humans are discussed in this review. Some of these antibodies appeared to be protective in animal models or in clinical trials, but discrepant results have been reported and the mechanism of the postulated protection was not clarified. The polyclonal antibody preparations have given variable results in patients. The clinical studies of anti-lipid A monoclonal antibodies seemed promising because both antibodies appeared to protect subsets of patients. However, the studies gave discrepant results concerning the type of patients reported to benefit from the administration of these antibodies. One of these antibodies, E5, appeared to improve the survival of patients with Gram-negative sepsis provided they were not in shock, but a second trial failed to confirm this. The other antibody, HA-1A, appeared to protect patients with Gram-negative sepsis who were in refractory shock, but only when they were bacteremic. This antibody was recently released on the market in some european countries. However, the FDA agency decided that a confirmatory study should be done before it could consider to approve HA-1A because a careful reanalysis suggested that the observed differences were only of marginal statistical significance. Therefore, this type of treatment has not yet clearly been shown to benefit patients. More studies are needed to delineate the role of core LPS antibodies in the management of Gram-negative sepsis.

Prophylactic intravenous administration of standard immune globulin as compared with core-lipopolysaccharide immune globulin in patients at high risk of postsurgical infection

BACKGROUND

Infections and their sequelae are a major cause of death among patients admitted to the surgical intensive care unit (ICU). Studies of passive immunotherapy with standard intravenous immune globulin and hyperimmune globulin directed against gram-negative core lipopolysaccharide to prevent gram-negative infections and their serious systemic complications have had equivocal results in such patients.

METHODS

We performed a double-blind study to assess the efficacy of standard immune globulin and core-lipopolysaccharide hyperimmune globulin in preventing infections in surgical patients at high risk. The patients received standard immune globulin (400 mg per kilogram of body weight), hyperimmune globulin (400 mg per kilogram), or placebo (25 percent albumin, 8 ml per kilogram) weekly, for a maximum of four doses while in the ICU.

RESULTS

A total of 352 patients were enrolled, and 329 could be evaluated. The number of patients in whom infections developed was significantly lower in the group receiving standard immune globulin than in the placebo group (36 of 109 vs. 53 of 112 patients, P = 0.03), as was the incidence of pneumonia (15 vs. 30 cases, P = 0.04), especially pneumonia due to gram-negative bacteria (5 vs. 16 cases, P = 0.02). The number of days spent in the ICU and the total days spent in the hospital were lower in the standard immune globulin group (medians of 2 and 7.5 days fewer; P = 0.02 and 0.06, respectively). In contrast, the hyperimmune globulin had no detectable prophylactic effect on infections (50 of 108 patients, with 25 cases of pneumonia). The rate of systemic infections and shock was similar in the three study groups, and hospital mortality did not differ significantly among them.

CONCLUSIONS

Intravenous immune globulin given prophylactically to selected high-risk patients in the surgical ICU can reduce the incidence of infection. Core-lipopolysaccharide hyperimmune globulin is not effective in preventing gram-negative infections and their systemic complications.

Use of mucin and hemoglobin in experimental murine gram-negative bacteremia enhances the immunoprotective action of antibodies reactive with the lipopolysaccharide core region

An antiserum with a high content of antibodies, binding to the Gram-negative lipopolysaccharide core region, was prepared by immunizing rabbits with the rough Escherichia coli mutant J5. This antiserum was capable of protecting mice against lethal challenge doses of E. coli 0 111:B4 in a mouse model where the animals were compromised by means of mucin plus hemoglobin (LD 50 = 10(3) bacteria). However, no protection was observed in a non-compromised mouse model (LD 50 = 10(7) bacteria). This observation might explain why in the past so many discrepant results have been obtained in mouse protection studies with cross-reactive antisera.

Antiserum against Escherichia coli J5: a re-evaluation of its in vitro and in vivo activity against heterologous gram-negative bacteria

Antiserum against Escherichia coli J5, a "rough" mutant of E. coli 0111, has been reported to confer broad-spectrum protection against serologically unrelated gram-negative bacteria. In order to re-evaluate these findings, we examined the influence of rabbit antiserum against E. coli J5 on the phagocytosis of heterologous gram-negative bacteria by rabbit granulocytes in vitro and its ability to protect mice against gram-negative bacterial infection. In vitro, J5 antiserum enhanced the phagocytosis of E. coli 0111, E. coli 06 and Serratia marcescens 06/014:H2 when compared to normal rabbit serum. However, J5 antiserum did not enhance the phagocytosis of Klebsiella pneumoniae type 2 and Pseudomonas aeruginosa serotype 9. In vivo, the protective effect of J5 antiserum against lethal gram-negative infection was not superior to that of normal (pre-immune) serum with the exception of E. coli 0111 septicemia. In contrast, type-specific antiserum against each of the smooth gram-negative bacteria markedly enhanced phagocytosis in vitro and exerted significant protection in vivo. Thus, in this study antiserum against E. coli J5 proved to be of limited value for opsonization of gram-negative bacteria and protection against gram-negative bacterial infection.