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.