Hemagglutinin response of human subjects to common enterobacterial antigen

Ten human volunteers were immunized intravenously with ethanol-soluble common enterobacterial antigen (CA) obtained from Escherichia coli O111. The immunogen contained 6 mg/ml, excluding salts. The antigen was given in amounts of 2 ml each in dilutions of 1:250 (48 mug) and 1:125 (96 mug), respectively, 1 week apart. Serum specimens were obtained prior to immunization and 1 week after the last injection. The CA hemagglutinins were titrated by means of the passive hemagglutination test, with CA from E. coli O14 as indicator antigen. The injections were well tolerated without side-effects by all subjects. A significant (> fourfold) increase in the titers of CA hemagglutinins was observed following immunization in 9 out of 10 volunteers. These results indicate the feasibility of immunization with CA of human subjects and suggest exploration of immunization against infection caused by Enterobacteriaceae producing this common enterobacterial antigen.