Immune response to Escherichia coli alpha-hemolysin in patients

The serum antibody response of patients infected with alpha-hemolysin (AH)-producing Escherichia coli was measured by three immunoassays: tube neutralization, microneutralization, and enzyme-linked immunosorbent assay. All three assay results showed good correlation with each other. The mean anti-AH titer in patients with E. coli infection was higher than the mean titer in noninfected patients. The hemolysin-neutralizing activity was immunoglobulin G. The amount of lipopolysaccharide (LPS) antibody did not correlate with the amount of AH antibody. LPS antibody measured by enzyme-linked immunosorbent assay was predominantly of the immunoglobulin G class. Adsorption of LPS antibody by E. coli H79 LPS did not affect anti-AH titers, indicating that LPS and AH have different antigenic determinants. AHs prepared from several different E. coli strains had identical or similar antigenic determinants at the active site. Hemolysin proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were stained identically by human sera with AH antibody and by a mouse monoclonal AH antibody.