Effects of IgM and IgG antibody in patients with bacteremia due to gram-negative bacilli

Earlier studies, which indicated that high titers of O-specific antibody to the patient's infecting organism in acute-phase serum specimens were not associated with a decrease in the frequency of subsequent shock and death in bacteremia due to gram-negative bacilli, were reexamined for evaluation of the protective activity of specific IgG and IgM antibody. Titers of hemagglutination antibody and levels of IgM, determined by indirect immunofluorescent staining of the patient's infecting organism, as well as hemagglutination titers after reduction of serum with 2-mercaptoethanol and IgG levels, correlated closely (P less than 0.001). High titers of IgG antibody to the patient's infecting organism in acute-phase specimens were associated with a significant reduction in the frequency of shock and death in bacteremia. In contrast, high titers of IgG antibody were not associated with a diminution in the frequency of shock and death. The previously demonstrated protective activity of antibody to an antigen, Re lipopolysaccharide, shared by most gram-negative bacilli was reconfirmed and shown to be independent of the protective activity of O-specific IgG antibody.