Protective activity of the antilipopolysaccharide antibodies from human cord serum.

We evaluated the ability of human maternal and cord serum antibodies to protect mice challenged with live Escherichia coli serotype O6:K2ac (E. coli O6). Mice received paired maternal or cord serum pools before a challenge with E. coli O6 to evaluate the mortality rate. All the pools were able to protect the animals challenged with bacteria except the test group from paired maternal and cord sera from preterm neonates containing less than 1.0 mg L(-1) immunoglobulin G antibody levels. In liver, spleen and mesenteric lymph nodes from the control group (phosphate-buffered saline), more than 10(2) CFU mL(-1) bacteria were found at 30 min and more than 10(5) CFU mL(-1) after 120 min. The test group showed lower bacterial counts in the organs, and no bacteria in the mesenteric lymph nodes during the evaluated period. Tumor necrosis factor alpha and interleukin 6 were undetectable in serum from animals pretreated with paired maternal and cord serum pools from full-term neonates and pools from preterm neonates containing high antibody and avidity levels. Our findings suggest that placental transfer of antilipopolysaccharide O6 immunoglobulin G antibodies to neonates has a high capacity to prevent lethal infection with E. coli O6 in a mouse protection model and that the degree of protection is determined by the concentration and avidity of these IgG antibodies.

Minimal concentration of human IgM and IgG antibodies necessary to protect mice from challenges with live O6 Escherichia coli.

This work evaluated the ability of human anti-lipopolysaccharide O6 IgM and IgG antibodies to protect mice challenged with Escherichia coli serotype O6 : K2ac. Purified IgM-effluent, purified IgG, pools of normal human serum (NHS), or control group were injected into mice 18 h before challenges with O6 E. coli. Interleukin 6 and tumor necrosis factor alpha were quantified in the sera of test and control groups. All mice receiving purified IgM-effluent (66.6 mg L(-1) of anti-lipopolysaccharide O6 IgM antibodies) and NHS survived. Purified IgG (1.1 mg L(-1) of anti-lipopolysaccharide O6 IgG antibodies) protected 87.5% of the animals. The control group showed no protective ability. The minimal concentration of anti-lipopolysaccharide O6 IgM antibodies, able to protect 50% of the animals was 33.3 mg L(-1) of purified IgM-effluent, whereas purified IgG was able to protect 50% of the animals with only 1.1 mg L(-1) of anti-lipopolysaccharide O6 IgG antibodies. Serum from animals pretreated with purified IgM-effluent and purified IgG before challenges with lipopolysaccharide O6 did not have detectable pro-inflammatory cytokines. Hepatocytes of the control group were completely invaded by bacteria, whereas none was found in animals pretreated with purified IgM-effluent and purified IgG. Higher concentrations of anti-lipopolysaccharide O6 IgM antibodies as compared to anti-lipopolysaccharide O6 IgG antibodies were needed to protect mice from challenges with E. coli O6 serotype.

Preterm and term neonates transplacentally acquire IgG antibodies specific to LPS from Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa.

High incidences of Gram-negative bacteria are found in neonatal nosocomial infections. Our aim was to investigate placental transmission of immunoglobulin G (IgG) reactive with lipopolysaccharide from Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli O111, O6 and O26. The total and lipopolysaccharide-specific IgM and IgG were determined in 11 maternal/umbilical-cord sera aged ≤33 weeks (GI); 21 aged >33 and <37 weeks (GII); and 32 term newborns (GIII). The total and lipopolysaccharide-specific IgM concentrations were equivalent in maternal sera. The total IgG concentrations were equivalent in maternal and newborn sera, with the exception of GIII newborns as compared with their mothers (P<0.0001) and with neonates from GI and GII (P<0.05). Lipopolysaccharide-specific IgG concentrations were lower in GI neonates than in their mothers (P<0.01) and lower in GII (P<0.05). Lower lipopolysaccharide-specific IgG levels were observed among neonates only for O111 in GI (P<0.05) and for O26 and Pseudomonas in GII, both as compared with GIII (P<0.05). The anti-lipopolysaccharide IgG transfer ratios were lower in GI (except for O26) and in GII (except for Klebsiella and O111) as compared with GIII (P<0.05). Our results suggest that the greater susceptibility to infections in preterm infants is influenced (besides the humoral response) by factors intrinsic and extrinsic to the condition of prematurity.