Human antibody responses to lipopolysaccharide after meningitis due to Haemophilus influenzae type b

Levels of serum antibodies to lipopolysaccharide (LPS) were measured in acute- and convalescent-phase sera from 27 patients with meningitis due to Haemophilus influenzae type b using an enzyme-linked immunosorbent assay. The geometric mean titers of antibodies to LPS in acute-phase sera were similar to those of 24 control children and 22 healthy adults. In convalescent-phase sera there was a fourfold increase in the geometric mean titers of IgG and IgM antibodies to LPS. The antibody responses wee independent of age and of antibody response to the type b capsule. However, the responses were bimodal: children with high levels of IgG and IgM antibodies to LPS in acute-phase sera did not respond with further increases in serum antibodies to LPS after infection, whereas children with lower initial levels showed high responses. The presence of high levels of antibodies to LPS in the sera of half of the acutely ill children suggests that antibodies to some LPS determinants are not protective.