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We prepared solutions of human IgM and IgG to various lipopolysaccharide (LPS) species. These were then tested, along with solutions of non-LPS specific human IgG or IgM, for their ability to confer passive immunity against experimental endotoxemia in two animal models. The immunoglobulins were first tested for an effect on the lethality induced by seven different LPSs in actinomycin-D sensitized mice, or by three different bacteria in normal mice. When the immunoglobulins were administered 1 h before challenge, a small protective effect was observed. This protection was dependent upon both the anti-LPS agent, the chemical composition of the LPS, or the strain of gram-negative bacteria used for injection. The anti-LPS IgM and IgG preparations reduced the mortality induced by Escherichia coli but not by Serratia marcescens or Klebsiella pneumoniae, indicating protection by strain-specific antibodies. When the antibodies were preincubated with LPS or bacteria for 30 min before administration, almost complete protection was seen. The influence of these immunoglobulin preparations or of human albumin (as a control) on the hypotensive and vascular-permeabilizing effects of LPS in rats was then studied. A dose-dependent inhibitory effect was observed with IgG preparations and albumin. At 200 mg/kg, anti-LPS IgG reduced the effects of LPS, while at 400 mg/kg, both anti-LPS and normal IgG preparations showed protection, as did human albumin used at the same dose. The IgM-enriched preparation worsened the initial hypotensive phase after LPS, whereas the anti-LPS IgM significantly reduced the second phase of the hypotension, but only at the largest dose of 400 mg/kg. In this second model using the rat, a clear difference between the activity of IgG and IgM was thus observed. We conclude that pretreatment with human immunoglobulins from large plasma pools modestly, but significantly, attenuated the effects of murine and rat Gram-negative sepsis, but that protection was incomplete. Our results suggest that single regimen intervention strategies may not be sufficient to influence the course of the disease.

To examine the influence of passive immunization on the biological fate of injected lipopolysaccharide (LPS), we used a human IgG preparation (anti-LPS IgG) rich in antibodies to a large panel of smooth and rough purified LPS extracts as well as a normal IgG preparation (standard IgG). Our approach was to compare the uptake of 125I-labeled LPS by the tissues of saline or IgG-treated rats. After intravenous injection, one fraction of 125I-labeled Escherichia coli O55:B5 LPS is rapidly taken up by tissues, while another fraction remained in the blood. Uptake of 125I-labeled LPS was principally observed into the liver and spleen. In rats treated prophylactically with standard IgG, these tissues accumulated significantly larger amount of LPS than the tissues of rats treated with anti-LPS IgG. Nevertheless, both IgG preparations increased the specific binding of LPS by the liver and spleen. High levels of homologous unlabeled LPS decreased the uptake of LPS by the liver, presumably by occupying tissue receptors, whereas in the presence of E. coli O127:B8 LPS, an increase of the uptake of 125I-labeled LPS by the liver and lungs was observed. The pharmacokinetics and tissue distribution of LPS-IgG complexes pre-formed in vitro were compared. In the presence of standard IgG, a unexpected increase of the uptake of LPS by the tissues was recorded, whereas LPS-anti-LPS IgG complexes decreased the binding of 125I-labeled LPS to the tissues. On the other hand, the vascular effects induced by LPS did not appear to be modified in rats pretreated with either IgG preparation. In conclusion, although passive immunization against LPS slightly modified the uptake and clearance of LPS, neither in vitro nor in vivo formation of LPS-anti-LPS IgG complexes afforded a very significant protection against the toxic effects of LPS.

We have developed an ELISA for IgM and IgG antibodies to the core glycolipid (CGL) of the Re mutant Salmonella minnesota R 595, and to lipid A. Anti-CGL antibodies have been detected in sera from 37% of healthy blood donors, whereas anti-lipid A activities were found in 13% of individuals only. The anti-CGL and anti-lipid A activities were examined in patients in a surgical intensive care unit, selected on the basis of a definite risk of infectious complications due to Gram-negative bacteria. Of the patients who developed such infections, the rate of favourable outcome was significantly higher in patients with either stable positive or increasing anti-CGL activities than in patients found to be negative. Our results provide clear evidence that anti-CGL antibodies contribute to host defence against various Gram-negative bacteria.